- Human Sensorimotor Control Laboratory,
School of Kinesiology,
University of Minnesota, U.S.A.
Jürgen Konczak
University of Minnesota, Kinesiology, Faculty Member
-
University of Minnesota, Center for Clinical Movement Science, Faculty Member add
-
Jürgen Konczak is a Full Professor in the School of Kinesiology at the University of Minnesota, where he is the head ... moreJürgen Konczak is a Full Professor in the School of Kinesiology at the University of Minnesota, where he is the head of the Human Sensorimotor Control Laboratory . He is also director of a university-wide Center for Clinical Movement Science that includes over 30 faculty from the allied health, clinical, engineering and movement sciences.Dr. Konczak’s research focuses on the neurophysiology and biomechanics of human motor function in clinical and special populations. He has published extensively in the area of neuromotor control, motor development and motor dysfunction due to neurological diseases such as ataxia, Parkinson's disease and dystonia. His research has been funded by the U.S. National Institutes of Health, the German Science Foundation and the European Commission. edit
Research Interests:
Research Interests:
Background Learning of a visuomotor task not only leads to changes in motor performance but also improves proprioceptive function of the trained joint/limb system. Such sensorimotor learning may show intra-joint transfer that is... more
Background Learning of a visuomotor task not only leads to changes in motor performance but also improves proprioceptive function of the trained joint/limb system. Such sensorimotor learning may show intra-joint transfer that is observable at a previously untrained degrees of freedom of the trained joint. Objective Here, we examined if and to what extent such learning transfers to neighboring joints of the same limb and whether such transfer is observable in the motor as well as in the proprioceptive domain. Documenting such intra-limb transfer of sensorimotor learning holds promise for the neurorehabilitation of an impaired joint by training the neighboring joints. Methods Using a robotic exoskeleton, 15 healthy young adults (18-35 years) underwent a visuomotor training that required them to make continuous, increasingly precise, small amplitude wrist movements. Wrist and elbow position sense just-noticeable-difference (JND) thresholds and spatial movement accuracy error (MAE) at wrist and elbow in an untrained pointing task were assessed before and immediately after, as well as 24 h after training. Results First, all participants showed evidence of proprioceptive and motor learning in both trained and untrained joints. The mean JND threshold decreased significantly by 30% in trained wrist (M: 1.26° to 0.88°) and by 35% in untrained elbow (M: 1.96° to 1.28°). Second, mean MAE in untrained pointing task reduced by 20% in trained wrist and the untrained elbow. Third, after 24 h the gains in proprioceptive learning persisted at both joints, while transferred motor learning gains had decayed to such extent that they were no longer significant at the group level. Conclusion Our findings document that a one-time sensorimotor training induces rapid learning gains in proprioceptive acuity and untrained sensorimotor performance at the practiced joint. Importantly, these gains transfer almost fully to the neighboring, proximal joint/limb system.
Research Interests:
This review provides a developmental perspective on our current understanding of the role of the cerebellum for sensorimotor and cognitive function. A synopsis on the contribution of the cerebellum on motor control, learning and cognition... more
This review provides a developmental perspective on our current understanding of the role of the cerebellum for sensorimotor and cognitive function. A synopsis on the contribution of the cerebellum on motor control, learning and cognition based on experiments in human adults and animals is presented. This knowledge is contrasted to the relevant literature on children and adolescents. Special attention is given to findings derived from lesion studies and clinical reports that examined the effect of cerebellar damage during development. In general, it is established that children may show the same sensorimotor deficits as adults as a result of cerebellar damage, while the findings of cognitive dysfunction in children are less clear and remain controversial. Younger children do not necessarily recover better than older children or adolescents. The sparing of the deep cerebellar nuclei and the extent of adjuvant chemo- or radiation therapy are better predictors of later motor and cognitive function in children and adolescents.
Research Interests:
Two hands, one perception: how bimanual haptic information is combined by the brain. J Neurophysiol 107: 544–550, 2012. First published October 26, 2011; doi:10.1152/jn.00756.2010.—Humans routinely use both of their hands to gather... more
Two hands, one perception: how bimanual haptic information is
combined by the brain. J Neurophysiol 107: 544–550, 2012. First
published October 26, 2011; doi:10.1152/jn.00756.2010.—Humans
routinely use both of their hands to gather information about shape
and texture of objects. Yet, the mechanisms of how the brain combines
haptic information from the two hands to achieve a unified
percept are unclear. This study systematically measured the haptic
precision of humans exploring a virtual curved object contour with
one or both hands to understand if the brain integrates haptic information
from the two hemispheres. Bayesian perception theory predicts
that redundant information from both hands should improve
haptic estimates. Thus exploring an object with two hands should
yield haptic precision that is superior to unimanual exploration. A
bimanual robotic manipulandum passively moved the hands of 20
blindfolded, right-handed adult participants along virtual curved contours.
Subjects indicated which contour was more “curved” (forced
choice) between two stimuli of different curvature. Contours were
explored uni- or bimanually at two orientations (toward or away from
the body midline). Respective psychophysical discrimination thresholds
were computed. First, subjects showed a tendency for one hand
to be more sensitive than the other with most of the subjects exhibiting
a left-hand bias. Second, bimanual thresholds were mostly within the
range of the corresponding unimanual thresholds and were not predicted
by a maximum-likelihood estimation (MLE) model. Third,
bimanual curvature perception tended to be biased toward the motorically
dominant hand, not toward the haptically more sensitive left
hand. Two-handed exploration did not necessarily improve haptic
sensitivity. We found no evidence that haptic information from both
hands is integrated using a MLE mechanism. Rather, results are
indicative of a process of “sensory selection”, where information from
the dominant right hand is used, although the left, nondominant hand
may yield more precise haptic estimates.
combined by the brain. J Neurophysiol 107: 544–550, 2012. First
published October 26, 2011; doi:10.1152/jn.00756.2010.—Humans
routinely use both of their hands to gather information about shape
and texture of objects. Yet, the mechanisms of how the brain combines
haptic information from the two hands to achieve a unified
percept are unclear. This study systematically measured the haptic
precision of humans exploring a virtual curved object contour with
one or both hands to understand if the brain integrates haptic information
from the two hemispheres. Bayesian perception theory predicts
that redundant information from both hands should improve
haptic estimates. Thus exploring an object with two hands should
yield haptic precision that is superior to unimanual exploration. A
bimanual robotic manipulandum passively moved the hands of 20
blindfolded, right-handed adult participants along virtual curved contours.
Subjects indicated which contour was more “curved” (forced
choice) between two stimuli of different curvature. Contours were
explored uni- or bimanually at two orientations (toward or away from
the body midline). Respective psychophysical discrimination thresholds
were computed. First, subjects showed a tendency for one hand
to be more sensitive than the other with most of the subjects exhibiting
a left-hand bias. Second, bimanual thresholds were mostly within the
range of the corresponding unimanual thresholds and were not predicted
by a maximum-likelihood estimation (MLE) model. Third,
bimanual curvature perception tended to be biased toward the motorically
dominant hand, not toward the haptically more sensitive left
hand. Two-handed exploration did not necessarily improve haptic
sensitivity. We found no evidence that haptic information from both
hands is integrated using a MLE mechanism. Rather, results are
indicative of a process of “sensory selection”, where information from
the dominant right hand is used, although the left, nondominant hand
may yield more precise haptic estimates.
Research Interests:
Proprioceptive training is a neurorehabilitation approach known to improve proprioceptive acuity and motor performance of a joint/limb system. Here, we examined if such learning transfers to the contralateral joints. Using a robotic... more
Proprioceptive training is a neurorehabilitation approach known to improve proprioceptive acuity and motor performance of a joint/limb system. Here, we examined if such learning transfers to the contralateral joints. Using a robotic exoskeleton, 15 healthy, right-handed adults (18–35 years) trained a visuomotor task that required making increasingly small wrist movements challenging proprioceptive function. Wrist position sense just-noticeable-difference thresholds (JND) and spatial movement accuracy error (MAE) in a wrist-pointing task that was not trained were assessed before and immediately as well as 24 h after training. The main results are: first, training reduced JND thresholds (− 27%) and MAE (− 33%) in the trained right wrist. Sensory and motor gains were observable 24 h after training. Second, in the untrained left wrist, mean JND significantly decreased (− 32%) at posttest. However, at retention the effect was no longer significant. Third, motor error at the untrained wri...
Research Interests:
Research Interests:
Ganganalysen im dreidimensionalen Raum basieren auf Zeit-Positionsdaten von Markern an relevanten Gelenkachsen (Winter 1987). Herkommliche Methoden gestatten die Analyse von 3D Translationen. Bei dieser Analyse ist die Berechnung von 3D... more
Ganganalysen im dreidimensionalen Raum basieren auf Zeit-Positionsdaten von Markern an relevanten Gelenkachsen (Winter 1987). Herkommliche Methoden gestatten die Analyse von 3D Translationen. Bei dieser Analyse ist die Berechnung von 3D Rotationen auf eine Ebene beschrankt. Die tatsachlich auftretenden Rotationen finden jedoch in mehreren Ebenen statt. Mit Hilfe einer neuartigen kinematischen Analyse, basierend auf der Mathematik der Quaternionen, sind wir in unserem Labor in der Lage, die Rotationen um alle Raumachsen zuverlassig zu berechnen. Die Position und die Orientierung von Korpersegmenten im Raum konnen mit dieser Methode vollstandig beschrieben werden.
Research Interests:
Background and Purpose— Loss of movement coordination is the main postacute symptom after cerebellar infarction. Although the course of motor recovery has been described previously, detailed kinematic descriptions of acute stage ataxia... more
Background and Purpose— Loss of movement coordination is the main postacute symptom after cerebellar infarction. Although the course of motor recovery has been described previously, detailed kinematic descriptions of acute stage ataxia are rare and no attempt has been made to link improvements in motor function to measures of neural recovery and lesion location. This study provides a comprehensive assessment of how lesion site and arm dysfunction are associated in the acute stage and outlines the course of upper limb motor recovery for the first 4 months after the infarction. Methods— Sixteen adult patients with cerebellar stroke and 11 age-matched healthy controls participated. Kinematics of goal-directed and unconstrained finger-pointing movements were measured at the acute stage and in 2-week and 3-month follow-ups. MRI data were obtained for the acute and 3-month follow-up sessions. A voxel-based lesion map subtraction analysis was performed to examine the effect of ischemic les...
Research Interests:
Discussion on the clinical relevance of activity-dependent plasticity after an insult to the developing brain is presented.
Research Interests:
Research Interests:
Research Interests:
SUMMARYBackgroundChronic low back pain (cLBP) affects the quality of life of 52 million Americans and leads to an enormous personal and economic burden. A multidisciplinary approach to cLBP management is recommended. Since medication has... more
SUMMARYBackgroundChronic low back pain (cLBP) affects the quality of life of 52 million Americans and leads to an enormous personal and economic burden. A multidisciplinary approach to cLBP management is recommended. Since medication has limited efficacy and there are mounting concerns about opioid addiction, the American College of Physicians and American Pain Society recommend non-pharmacological interventions, such as mind and body approaches (e.g., Qigong, yoga, Tai Chi) before prescribing medications. Of those, Qigong practice might be most accessible given its gentle movements and because it can be performed standing, sitting, or lying down. The three available Qigong studies in adults with cLBP showed that Qigong reduced pain more than waitlist and equally well than exercise. Yet, the duration and/or frequency of Qigong practice were low (<12 weeks or less than 3x/week). The objectives of this study were to investigate the feasibility of practicing Spring Forest Qigong™ or...
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
With a growing interest in real-time control of prostheses and wearable rehabilitation devices to treat motor dysfunction, there is a need to classify normal and abnormal body movement using kinematic and electrophysiological data. This... more
With a growing interest in real-time control of prostheses and wearable rehabilitation devices to treat motor dysfunction, there is a need to classify normal and abnormal body movement using kinematic and electrophysiological data. This paper presents a novel linear algorithm that can classify 10 distinct neck movements based on signals of only four surface electromyography (sEMG) electrodes. We here report on data of 5 healthy adults performing the 10 different neck movements: flexion/extension, right/left lateral flexion, right/left rotation, and four multiplanar directions. Surface EMG electrodes were attached to five locations: 1) left and right sternocleidomastoid, 2) left and right trapezius, and 3) the C7 spinal segment as reference. The algorithm yielded an accuracy of 92.5% in classifying six single-planar neck movement directions and an average accuracy of 81.2% in classifying all ten directions. The algorithm's performance was validated by comparing its accuracy with ...
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Cognitive Science, Computer Vision, Cognition, Binocular vision, Motor Control, and 15 moreMedicine, Humans, Depth, Depth Perception, Cues, Female, Male, Distance Perception, Adult, Analysis of Variance, Neuropsychologia, Monocular Vision, Human Visual System, Neurosciences, and Functional Laterality
Research Interests:
Neuroscience, Psychology, Cognitive Science, Magnetoencephalography, Medicine, and 15 moreTactile Perception, Somatosensory Neuroscience, Brain Mapping, Humans, Female, Male, Somatosensory Cortex, Adult, Stimulation, Fingers, Neurosciences, Time varying, Functional Laterality, Thumb, and Somatosensory system
Research Interests:
Nine young infants were followed longitudinally from 4 to 15 months of age. We recorded early spontaneous movements and reaching movements to a stationary target. Time-position data of the hand (endpoint), shoulder, and elbow were... more
Nine young infants were followed longitudinally from 4 to 15 months of age. We recorded early spontaneous movements and reaching movements to a stationary target. Time-position data of the hand (endpoint), shoulder, and elbow were collected using an optoelectronic measurement system (ELITE). We analyzed the endpoint kinematics and the intersegmental dynamics of the shoulder and elbow joint to investigate how changes in proximal torque control determined the development of hand trajectory formation. Two developmental phases of hand trajectory formation were identified: a first phase of rapid improvements between 16 and 24 weeks of age, the time of reaching onset for all infants. During that time period the number of movement units per reach and movement time decreased dramatically. In a second phase (28-64 weeks), a period of &quot;fine-tuning&quot; of the sensorimotor system, we saw slower, more gradual changes in the endpoint kinematics. The analysis of the underlying intersegmental joint torques revealed the following results: first, the range of muscular and motion-dependent torques (relative to body weight) did not change significantly with age. That is, early reaching was not confined by limitations in producing task-adequate levels of muscular torque. Second, improvements in the endpoint kinematics were not accomplished by minimizing amplitude of muscle and reactive torques. Third, the relative timing of muscular and motion-dependent torque peaks showed a systematic development toward an adult timing profile with increasing age. In conclusion, the development toward invariant characteristics of the hand trajectory is mirrored by concurrent changes in the control of joint forces. The acquisition of stable patterns of intersegmental coordination is not achieved by simply regulating force amplitude, but more so by modulating the correct timing of joint force production and by the system&#39;s use of reactive forces. Our findings support the view that development of reaching is a process of unsupervised learning with no external or innate teacher prescribing the desired kinematics or kinetics of the movement.
Research Interests:
This study examines the phenomenon of attrition of German adults living in an L2 environment. Recent studies have revealed the selective and ordered character of arising attrition. Our reference frame permits us to hypothesize a modular... more
This study examines the phenomenon of attrition of German adults living in an L2 environment. Recent studies have revealed the selective and ordered character of arising attrition. Our reference frame permits us to hypothesize a modular organization of languages (Fodor, on 1983; paradise, on 1997) with a hierarchic treatment (’data-/concept-driven’: Durgunoglu & Roedinger, 1987). This hypothesis is notably based on a model of oral production (Levelt, on 1989) that has been later adapted to comprehension by De Bot (1992). The aims of our study are to differentiate the vulnerability of different linguistic levels, in order to reveal the organization of both languages in the paradigm of natural reading (= modality of perception of written stimuli) and to test whether the hypothesis of temporally inhibited access (Paradise, 1985, 1993, etc) or the hypothesis of reorganization in a highly dynamic system (Pavlenko, 2000) fits better to our results. In order to reveal an eventual attrition, we measured eye-movements of the participants in relation to French-German interferences on lexical, morphological and semantic levels by using an eye-tracking system, which is a non-interfering psycho-physiological method. The dichotomy between high and low processing proved to be important to understand different eye-fixation indications. Longer initial fixations for sentences containing interferences reflect the detection of an anomaly. The higher probability and length of eye-refixations for morphological and semantic interferences seems to prove the implication of high level (concept-driven) processing. Thus, Levelt’s model (1989) which classifies morphological and phonological items on the level of lexemes cannot be supported.
Research Interests:
Research Interests:
Research Interests:
Proprioception is the sense of the body awareness. Proprioceptive deficits represent frequent consequences of several neurological conditions like stroke,... more
Proprioception is the sense of the body awareness. Proprioceptive deficits represent frequent consequences of several neurological conditions like stroke, Parkinson&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;s disease and others. The assessment of such somatosensory function is crucial, although the available clinical tests are not sensitive enough. The human wrist is a crucial joint for many activities of daily living and to address the lack of its characterization in terms of proprioceptive acuity the authors in previous studies proposed a novel method that combined the use of a 3-DoF robot and a threshold haunting paradigm. Further experiments were performed to characterize the proprioceptive acuity of the dominant wrist for adduction, extension, pronation and supination by using a 2-alternative-forced-choice test. The acuity thresholds obtained from six subjects (mean values ± standard deviation of 1.65±0.39 for extension, 1.13±0.34 for adduction, 1.90±0.58 for pronation and 1.70±0.30 for supination) were finally combined with the ones harvested in the previous studies for flexion and abduction in order to build the first comprehensive database of human wrist proprioceptive acuity.
Research Interests:
Upper limb robotic rehabilitation technology has recognized the importance of biofeedback signals for optimizing motor recovery. Impaired motor control is typically associated with abnormal muscle activation patterns and such patterns can... more
Upper limb robotic rehabilitation technology has recognized the importance of biofeedback signals for optimizing motor recovery. Impaired motor control is typically associated with abnormal muscle activation patterns and such patterns can be revealed by electromyography (EMG). However, before using user-generated EMG signals as biofeedback for controlling and optimizing force output of a robot, it is imperative that the healthy muscle innervation patterns are fully established to guide possible robot-aided rehabilitation protocols. Given the muscular redundancy found in many human limb systems, and given that force generation of human muscles is not linear, it becomes important to understand how synergistic control influences joint force and joint kinematics. It is the purpose of this study to map the electromyographic activation patterns of the major human muscles involved in controlling the hand/wrist system. By means of a robotic exoskeleton three Degrees of Freedom (DoF) were evaluated: wrist flexion-extension and adduction-abduction as well as forearm pronation-supination separately and for different ranges of the workspace. We recorded EMG activity of 7 arm muscles of 4 healthy subjects performing the task and we therefore defined the typical EMG activation patterns of such muscles during robotic training.
Research Interests:
Research Interests:
Psychology, Perception, Aging, Haptic Perception, Medicine, and 15 morePhysical Medicine and Rehabilitation, Proprioception, Brain, Humans, Form perception, Female, Male, Aged, Middle Aged, Adult, Haptic Technology, Parkinson Disease, Case Control Studies, Psychology and Cognitive Sciences, and Medical and Health Sciences
Proprioceptive function can become enhanced during motor learning. Yet, we have incomplete knowledge to what extent proprioceptive function is trainable and how a training that enhances proprioception may influence performance in... more
Proprioceptive function can become enhanced during motor learning. Yet, we have incomplete knowledge to what extent proprioceptive function is trainable and how a training that enhances proprioception may influence performance in untrained motor skills. To address this knowledge gap, healthy young adults (N = 14) trained in a visuomotor task that required learners to make increasingly accurate wrist movements. Using a robotic exoskeleton coupled with a virtual visual environment, participants tilted a virtual table through continuous wrist flexion/extension movements with the goal to position a rolling ball on table into a target. With learning progress, the level of difficulty increased by altering the virtual ball mechanics and the gain between joint movement and ball velocity. Before and after training, wrist position sense acuity and spatial movement accuracy in an untrained, discrete wrist-pointing task was assessed using the same robot. All participants showed evidence of prop...
Research Interests:
Research Interests:
Cognitive Science, Functional MRI, Brain Mapping, Classical Conditioning, Humans, and 15 moreCerebellum, Close relationships, Chronic Disease, Cerebellar ataxia, Brain Ischemia, High Resolution, Clinical Data, Degeneration, Ataxia, Cerebellar Cortex, Healthy Subjects, Blinking, Functional Laterality, Acute Disease, and cerebral arteries
Proprioception is central for motor control and its role must also be taken into account when designing motor rehabilitation training protocols. This is particularly important when dealing with motor deficits due to proprioceptive... more
Proprioception is central for motor control and its role must also be taken into account when designing motor rehabilitation training protocols. This is particularly important when dealing with motor deficits due to proprioceptive impairment such as peripheral sensory neuropathy. In these cases substituting or augmenting diminished proprioceptive sensory information might be beneficial for improving motor function. However it still remains to be understood how proprioceptive senses can be improved by training, how this would translate into motor improvement and whether additional sensory modalities during motor training contribute to the sensorimotor training process. This preliminary study investigated how proprioceptive/haptic training can be augmented by providing additional sensory information in the form of vibro-tactile feedback. We tested the acuity of the wrist proprioceptive position sense before and after robotic training in two groups of healthy subjects, one trained only with haptic feedback and one with haptic and vibro-tactile feedback. We found that only the group receiving the multimodal feedback significantly improved proprioceptive acuity. This study demonstrates that non-proprioceptive position feedback derived from another somatosensory modality is easily interpretable for humans and can contribute to an increased precision of joint position. The clinical implications of this finding will be outlined.
Research Interests:
Research Interests:
Research Interests:
Neurological movement disorders such as stroke or sensory neuropathy are associated with somatosensory deficits. From a neurorehabilitation perspective, the assessment of proprioceptive function is important for planning and applying... more
Neurological movement disorders such as stroke or sensory neuropathy are associated with somatosensory deficits. From a neurorehabilitation perspective, the assessment of proprioceptive function is important for planning and applying adequate rehabilitation treatments. Numerous behavioral and psychophysical methods are available to measure proprioceptive acuity. However, no universally accepted and adopted protocol exists. In recent years robotic devices have increasingly been used to investigate and assess proprioceptive function, but few studies have focused on the wrist joint. To fill this knowledge gap, this study aimed to systematically map the proprioceptive acuity of the wrist for its two joint degrees of freedom (DoF) - flexion/extension (FE) and abduction/adduction (AA). Twenty eight healthy young adults performed an ipsilateral, active joint position matching task using a robotic device. As a measure of proprioceptive acuity we determined the error between target position and the matched joint position. Results showed that: first, proprioceptive acuity varied between the two joint DoF with the matching error for AA being lower than the FE. Second, within each DoF, the motion direction did not affect the accuracy. Third, the radial component of the matching error showed DoF dependence: the FE movements tended to undershoot, while the AA movement overshot the target position. Results are indicative of a joint DoF dependent anisotropy of wrist proprioceptive acuity.
Research Interests:
Research Interests:
Neuroscience, Magnetic Resonance Imaging, Exercise therapy, Medicine, Brain, and 15 moreHumans, Cerebellum, Female, Male, Neuronal Plasticity, Aged, Middle Aged, Adult, Analysis of Variance, Cerebellar Degeneration, Motor activity, Disability Evaluation, Cerebellar Diseases, Medical and Health Sciences, and physical exertion
Research Interests:
Cognitive Science, Ultrasound, Postural Control, Adolescent, Medicine, and 15 moreHumans, Child, Cerebellum, Female, Male, Posture, High Resolution, Adult, Balance control, Postural Balance, Neurosciences, Biomechanical Phenomena, Deep cerebellar nuclei, Postoperative Complications, and Base of support
Research Interests:
This study examined the effects of posterior fossa tumor surgery and concomitant irradiation and/or chemotherapy on the long-term recovery of balance function in children and adolescent patients. 22 patients, treated during childhood for... more
This study examined the effects of posterior fossa tumor surgery and concomitant irradiation and/or chemotherapy on the long-term recovery of balance function in children and adolescent patients. 22 patients, treated during childhood for a benign (n = 14) or malignant cerebellar tumor (n = 8), were examined in chronic state (mean latency between surgery and testing: 7.7 years, range 3 - 17 years). Postural impairments were assessed with static and dynamic posturography. All cerebellar lesions were documented by standardized and normalized MRI data. Healthy age- and gender-matched subjects served as a control group. Comparing the balance function of (i) children with or without affected cerebellar nuclei and (ii) children with and without adjuvant chemotherapy and/or radiotherapy revealed that damage to the cerebellar nuclei had more impact on neurological impairment than concomitant tumor therapy. Balance abnormalities were most pronounced when a lesion affected the fastigial nucleus. Chemotherapy with its neurological side effect was associated with enhanced postural sway in only two children with malignant tumors. The study results indicate that the sparing of the deep cerebellar nuclei had the greatest impact on the recovery of balance function in pediatric patients treated for both a benign or malignant cerebellar tumor.
Research Interests:
Magnetic Resonance Imaging, Adolescent, Medicine, Humans, Child, and 15 moreCerebellum, Female, Male, Infant, Children and Adolescents, Neuropediatrics, Postural Balance, ADJUVANT THERAPY, Neurosciences, Nino, Postoperative Complications, Neurologic Examination, Combined Modality Therapy, Child preschool, and Paediatrics and reproductive medicine
Research Interests:
Research Interests:
BackgroundThe importance of assessing proprioceptive function for rehabilitation after neurological or orthopedic injury has long been recognized. Yet, neither the validity nor the accuracy of the available tests is firmly established.... more
BackgroundThe importance of assessing proprioceptive function for rehabilitation after neurological or orthopedic injury has long been recognized. Yet, neither the validity nor the accuracy of the available tests is firmly established. Testing typically involves repeated matching of a given joint position with the same or opposite limb where the difference between the 2 positions indicates proprioceptive acuity.ObjectivesThe aim of this study was to compare position sense acuity between ipsilateral and contralateral matching methods against a psychophysical threshold method to establish the accuracy and relationships between these models.DesignA repeated-measures design was used.MethodAssessment of forearm position sense for a 10-degree reference position in 27 young adults who were healthy.ResultsPsychophysical thresholds were revealed to be the most precise and least variable acuity measure. The mean (±SD) threshold (1.05°±0.47°) was significantly lower than mean position errors o...
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Psychology, Algorithms, Perception, Aging, Haptics, and 15 moreHaptic Perception, Adolescent, Humans, Child, Form perception, Female, Male, Feedback, Computer User Interface Design, Adult, Haptic Technology, Exploratory Behavior, Functional Laterality, Psychology and Cognitive Sciences, and Medical and Health Sciences
NEW & NOTEWORTHY: Neurodegeneration of the cerebellum progresses over years and primarily affects cerebellar cortex. It leads to a progressive loss of control and coordination of movement. We here show that the neurodegenerative process... more
NEW & NOTEWORTHY: Neurodegeneration of the cerebellum progresses over years and primarily affects cerebellar cortex. It leads to a progressive loss of control and coordination of movement. We here show that the neurodegenerative process not only leads to cells loss in cerebellar cortex but also induces neurostructural changes in the form of increased gray matter in the efferent targets of the cerebellar cortex, namely, the cerebellar output nuclei, the SMA, and premotor cortex.
Research Interests:
This review addresses the role of exercise as an intervention for treating neurological disease. It focuses on three major neurological diseases that either present in acute or neurodegenerative forms—Parkinson’s disease, cerebellar... more
This review addresses the role of exercise as an intervention for treating neurological disease. It focuses on three major neurological diseases that either present in acute or neurodegenerative forms—Parkinson’s disease, cerebellar ataxia, and cortical stroke. Each of the diseases affects primarily different brain structures, namely the basal ganglia, the cerebellum, and the cerebrum. These structures are all known to be involved in motor control, and the dysfunction of each structure leads to distinct movement deficits. The review summarizes current knowledge on how exercise can aid rehabilitation or therapeutic efforts. In addition, it addresses the role of robotic devices in enhancing available therapies by reviewing how robot-aided therapies may promote the recovery for stroke survivors. It highlights recent scientific evidence in support of exercise as a treatment for brain dysfunction, but also outlines the still open challenges for unequivocally demonstrating the benefits of...
Research Interests:
Research Interests:
Background: The cerebellum plays an important role for balance control and the coordination of voluntary movements. Beyond that there is growing evidence that the cerebellum is also involved in cognitive functions. How ataxic motor... more
Background: The cerebellum plays an important role for balance control and the coordination of voluntary movements. Beyond that there is growing evidence that the cerebellum is also involved in cognitive functions. How ataxic motor symptoms are influenced by simultaneous performance of a cognitive task, however, has rarely been assessed and some of the findings are contradictory. We assessed stance in 20 patients with adult onset degenerative almost purely cerebellar disorders and 20 healthy controls during single and dual task conditions (verbal working memory task). To objectively measure postural sway and the impact of somatosensory, visual and vestibular inputs we used static and dynamic posturography with the Sensory Organization Test (SOT). Results: In both groups, cerebellar patients and controls, dual tasking reduced all sway parameters. Reduction of sway path was higher in cerebellar patients and increased with the difficulty of the postural task. The frequency of falls was higher in the patients group especially during the more challenging conditions and dual task performance in particular increased the risk of falls in cerebellar patients.
Research Interests:
Neurological movement disorders such as stroke or sensory neuropathy are associated with somatosensory deficits. From a neurorehabilitation perspective, the assessment of proprioceptive function is important for planning and applying... more
Neurological movement disorders such as stroke or sensory neuropathy are associated with somatosensory deficits. From a neurorehabilitation perspective, the assessment of proprioceptive function is important for planning and applying adequate rehabilitation treatments. Numerous behavioral and psychophysical methods are available to measure proprioceptive acuity. However, no universally accepted and adopted protocol exists. In recent years robotic devices have increasingly been used to investigate and assess proprioceptive function, but few studies have focused on the wrist joint. To fill this knowledge gap, this study aimed to systematically map the proprioceptive acuity of the wrist for its two joint degrees of freedom (DoF)-flexion/extension (FE) and abduction/adduction (AA). Twenty eight healthy young adults performed an ipsilateral, active joint position matching task using a robotic device. As a measure of proprioceptive acuity we determined the error between target position and the matched joint position. Results showed that: first, proprioceptive acuity varied between the two joint DoF with the matching error for AA being lower than the FE. Second, within each DoF, the motion direction did not affect the accuracy. Third, the radial component of the matching error showed DoF dependence: the FE movements tended to undershoot, while the AA movement overshot the target position. Results are indicative of a joint DoF dependent anisotropy of wrist proprioceptive acuity.
Research Interests:
Objective: Numerous reports advocate that training of the proprioceptive sense is a viable behavioral therapy for improving impaired motor function. However, there is little agreement of what constitutes proprioceptive training and how... more
Objective: Numerous reports advocate that training of the proprioceptive sense is a viable behavioral therapy for improving impaired motor function. However, there is little agreement of what constitutes proprioceptive training and how effective it is. We therefore conducted a comprehensive, systematic review of the available literature in order to provide clarity to the notion of training the proprioceptive system. Methods: Four major scientific databases were searched. The following criteria were subsequently applied: (1) A quantified pre-and post-treatment measure of proprioceptive function. (2) An intervention or training program believed to influence or enhance proprioceptive function. (3) Contained at least one form of treatment or outcome measure that is indicative of somatosensory function. From a total of 1284 articles, 51 studies fulfilled all criteria and were selected for further review. Results: Overall, proprioceptive training resulted in an average improvement of 52% across all outcome measures. Applying muscle vibration above 30 Hz for longer durations (i.e., min vs. s) induced outcome improvements of up to 60%. Joint position and target reaching training consistently enhanced joint position sense (up to 109%) showing an average improvement of 48%. Cortical stroke was the most studied disease entity but no clear evidence indicated that proprioceptive training is differentially beneficial across the reported diseases. Conclusions: There is converging evidence that proprioceptive training can yield meaningful improvements in somatosensory and sensorimotor function. However, there is a clear need for further work. Those forms of training utilizing both passive and active movements with and without visual feedback tended to be most beneficial. There is also initial evidence suggesting that proprioceptive training induces cortical reorganization, reinforcing the notion that proprioceptive training is a viable method for improving sensorimotor function.
Research Interests:
Focal dystonia of the head and neck are associated with a loss of kinesthetic acuity at muscles distant from the dystonic sites. That is, while the motor deficits in focal dystonia are confined, the associated somatosensory deficits are... more
Focal dystonia of the head and neck are associated with a loss of kinesthetic acuity at muscles distant from the dystonic sites. That is, while the motor deficits in focal dystonia are confined, the associated somatosensory deficits are generalized. This is the first systematic study to examine, if patients diagnosed with spasmodic dystonia (SD) show somatosensory impairments similar in scope to other forms of focal dystonia.
Research Interests:
Impaired proprioception severely affects the control of gross and fine motor function. However, clinical assessment of proprioceptive deficits and its impact on motor function has been difficult to elucidate. Recent advances in haptic... more
Impaired proprioception severely affects the control of gross and fine motor function. However, clinical assessment of proprioceptive deficits and its impact on motor function has been difficult to elucidate. Recent advances in haptic robotic interfaces designed for sensorimotor rehabilitation enabled the use of such devices for the assessment of proprioceptive function.
Research Interests:
The importance of assessing proprioceptive function for rehabilitation after neurological or orthopedic injury has long been recognized. Yet, neither the validity nor the accuracy of the available tests is firmly established. Testing... more
The importance of assessing proprioceptive function for rehabilitation after neurological or orthopedic injury has long been recognized. Yet, neither the validity nor the accuracy of the available tests is firmly established. Testing typically involves repeated matching of a given joint position with the same or opposite limb where the difference between the 2 positions indicates proprioceptive acuity. The aim of this study was to compare position sense acuity between ipsilateral and contralateral matching methods against a psychophysical threshold method to establish the accuracy and relationships between these models. A repeated-measures design was used. Assessment of forearm position sense for a 10-degree reference position in 27 young adults who were healthy. Psychophysical thresholds were revealed to be the most precise and least variable acuity measure. The mean (SD) threshold (1.05°0.47°) was significantly lower than mean position errors obtained by both joint position matching tasks (ipsilateral: 1.51°0.64°; contralateral: 1.84°0.73°)—a 44% to 75% difference in measurement accuracy. Individual participant position errors correlated poorly with respective thresholds, indicating a lack of concurrent validity. Position errors for both matching methods correlated only mildly with each other. The data represent performance of a healthy, young adult cohort. Differences between methods will likely be more pronounced in aging and clinical populations. Threshold testing and joint position matching methods examine different physiological aspects of proprioceptive function. Because threshold testing is based on passive motion, it most closely reflects afferent sensory feedback processing (ie, proprioception). Matching methods require active motion and are consequently influenced by additional sensorimotor processes. Factors such as working memory and transmission between brain hemispheres also influence joint matching task outcomes.
Research Interests:
Ataxia refers to a lack or loss of movement coordination. It is associated with damage or dysfunction of the cerebellum or its afferent and efferent projections.1 Ataxia is especially debilitating for children because they are still... more
Ataxia refers to a lack or loss of movement coordination. It is associated with damage or dysfunction of the cerebellum or its afferent and efferent projections.1 Ataxia is especially debilitating for children because they are still developing and learning motor competency. 2 Childhood ataxia can have hereditary causes, such as ataxia telangiectasia, or acquired causes, such as infection or tumor. The duration of ataxia varies greatly: from short, transient episodes, such as post infectious cerebellar demyelination,3 to lifelong conditions, such as Dandy-Walker syndrome. The prevalence of some ataxia-causing conditions has been reported. However, most reports are focused on a single condition and a specific geographical location, making it difficult to generalize the prevalence estimates. Furthermore, few studies separate the prevalence of ataxia in children vs adults.4–12 Given the multitude of ataxia-causing conditions and recognizing that each can be quite rare, the overall prevalence of childhood ataxia is likely underestimated. Yet overall prevalence data are needed to accurately assess the impact and societal cost of childhood ataxia. The purpose of this article is to systematically review the literature on the prevalence of ataxia in children across World Health Organization (WHO) regions. The prevalence of childhood ataxia is estimated by systematically examining prevalence estimates for the many different causes of childhood ataxia.
Research Interests:
Recent research indicates that physiotherapy can improve motor performance of patients with cerebellar degeneration. Given the known contributions of the cerebellum to motor learning, it remains unclear whether such observable changes in... more
Recent research indicates that physiotherapy can improve motor performance of patients with cerebellar degeneration. Given the known contributions of the cerebellum to motor learning, it remains unclear whether such observable changes in performance are mediated by the cerebellum or cerebral brain areas involved in motor control and learning. The current study addressed this question by assessing the increase in gray matter volume due to sensorimotor training in cerebellar patients using voxel-based morphometry. Nineteen human subjects with pure cerebellar degeneration and matched healthy controls were trained for 2 weeks on a balance task. Postural and clinical assessments along with structural magnetic resonance imaging were performed pretraining and post-training. The main findings were as follows. First, training enhanced balance performance in cerebellar patients. Second, in contrast to controls patients revealed significantly more post-training gray matter volume in the dorsal premotor cortex. Third, training-related increase in gray matter volume was observed within the cerebellum and was more pronounced in controls than in patients. However, statistically cerebellar changes were at the trend level and thus require additional, independent confirmation. We conclude that sensorimotor training of patients with cerebellar neurodegeneration induces gray matter changes primarily within nonaffected neocortical regions of the cerebellar-cortical loop. Residual function of the cerebellum appears to be exploited suggesting either a recovery from degeneration or intact processes of cerebellar plasticity in the remaining healthy tissue.
Research Interests:
A B S T R AC T : An established treatment for the motor symptoms of Parkinson's disease (PD) is deep brain stimulation (DBS) of the subthalamic nucleus (STN). Mounting evidence suggests that PD is also associated with somatosensory... more
A B S T R AC T : An established treatment for the motor symptoms of Parkinson's disease (PD) is deep brain stimulation (DBS) of the subthalamic nucleus (STN). Mounting evidence suggests that PD is also associated with somatosensory deficits, yet the effect of STN-DBS on somatosensory processing is largely unknown. This study investigated whether STN-DBS affects somatosen-sory processing, specifically the processing of tactile and proprioceptive cues, by systematically examining the accuracy of haptic perception of object size. (Haptic perception refers to one's ability to extract object features such as shape and size by active touch.) Without vision, 13 PD patients with implanted STN-DBS and 13 healthy controls haptically explored the heights of 2 successively presented 3-dimensional (3D) blocks using a precision grip. Participants verbally indicated which block was taller and then used their nonprobing hand to motorically match the perceived size of the comparison block. Patients were tested during ON and OFF stimulation , following a 12-hour medication washout period. First, when compared to controls, the PD group's haptic discrimination threshold during OFF stimulation was elevated by 192% and mean hand aperture error was increased by 105%. Second, DBS lowered the haptic discrimination threshold by 26% and aperture error decreased by 20%. Third, during DBS ON, probing with the motorically more affected hand decreased haptic precision compared to probing with the less affected hand. This study offers the first evidence that STN-DBS improves haptic precision, further indicating that somato-sensory function is improved by STN-DBS. We conclude that DBS-related improvements are not explained by improvements in motor function alone, but rather by enhanced somatosensory processing. V C 2013 International Parkinson and Movement Disorder Society
Research Interests:
Musician's dystonia (MD) is a neurological motor disorder characterized by involuntary contractions of those muscles involved in the play of a musical instrument. It is task-specific and initially only impairs the voluntary control of... more
Musician's dystonia (MD) is a neurological motor disorder characterized by involuntary contractions of those muscles involved in the play of a musical instrument. It is task-specific and initially only impairs the voluntary control of highly practiced musical motor skills. MD can lead to a severe decrement in a musician's ability to perform. While the etiology and the neurological pathomechanism of the disease remain unknown, it is known that MD like others forms of focal dystonia is associated with somatosensory deficits, specifically a decreased precision of tactile and proprioceptive perception. The sensory component of the disease becomes also evident by the patients' use of “sensory tricks” such as touching dystonic muscles to alleviate motor symptoms. The central premise of this paper is that the motor symptoms of MD have a somatosensory origin and are not fully explained as a problem of motor execution. We outline how altered proprioceptive feedback ultimately leads to a loss of voluntary motor control and propose two scenarios that explain why sensory tricks are effective. They are effective, because the sensorimotor system either recruits neural resources normally involved in tactile-proprioceptive (sensory) integration, or utilizes a fully functioning motor efference copy mechanism to align experienced with expected sensory feedback. We argue that an enhanced understanding of how a primary sensory deficit interacts with mechanisms of sensorimotor integration in MD provides helpful insights for the design of more effective behavioral therapies.
Research Interests:
Humans routinely estimate the size and weight of objects. Yet, when lifting two objects of equal weight but different size, they often perceive the smaller object as being heavier. This size–weight illusion (SWI) is known to have a lesser... more
Humans routinely estimate the size and weight of objects. Yet, when lifting two objects of equal weight but different size, they often perceive the smaller object as being heavier. This size–weight illusion (SWI) is known to have a lesser effect on motor control of object lifting. How the nervous system combines ''weight'' and ''size'' cues with prior experience and whether these cues are differentially integrated for perception and sensorimotor action is still not fully understood. Therefore, we assessed not only whether the experience of size biases weight perception , but also if experience of weight biases the size perception of objects. Further, to investigate differences between perceptual and motor systems for cue-experience integration, participants haptically explored the weight of an object with one hand and then shaped the aperture of their other hand to indicate its perceived size. Results—First, next to a SWI, healthy adults (N = 21) perceived lighter objects as being smaller and heavier objects as being larger, demonstrating a weight–size illusion (WSI). Second, participants were more susceptible to either the SWI or WSI. Third, aperture of the non-exploring hand was scaled to perceived weight and not to physical size. Hand openings were consistently smaller than physical size, with SWI-sensitive participants being significantly more affected than WSI-sensitive subjects. We conclude: first, both size and weight perceptions are biased by prior experience. Weight perception is biased by expectations of size, while size perception is influenced by the expectancy of weight. Second, humans have the tendency to use one cue predominantly for both types of perception. Third, combining perceived weight with expected size influenced hand motor control, while online haptic feedback was largely ignored. Finally, we present a processing model underlying the size–weight cue integration for the perceptual and motor system.
Research Interests:
Neural processes of sensory-motor- and motor sensory integration link perception and action, forming the basis for human interaction with the environment. Haptic perception, the ability to extract object features through action, is based... more
Neural processes of sensory-motor- and motor sensory integration link perception and action, forming the basis for human interaction with the environment. Haptic perception, the ability to extract object features through action, is based on these processes. To study the development of motor-sensory integration, children judged the curvature of virtual objects after exploring them actively or while guided passively by a robot. Haptic acuity reached adult levels only at early adolescence. Unlike in adults, haptic precision in children was consistently lower during active exploration when compared to passive motion. Thus, the exploratory movements themselves constitute a form of noise for the developing haptic system that younger brains cannot compensate until mid-adolescence. Computationally, this is consistent with a noisy efference copy mechanism producing imprecise predicted sensory feedback, which compromises haptic precision in children, while the mature mechanism aids the adult brain to account for the effect of self-generated motion on perception.
Research Interests:
This study investigated how Parkinson’s disease alters haptic perception and the underlying mechanisms of somatosensory and sensorimotor integration. Changes in haptic sensitivity and acuity (the abilities to detect and to discriminate... more
This study investigated how Parkinson’s disease alters haptic perception and the underlying mechanisms of somatosensory and sensorimotor integration. Changes in haptic sensitivity and acuity (the abilities to detect and to discriminate between haptic stimuli) due to Parkinson’s disease were systematically quantified and contrasted to the performance of healthy older and young adults. Using a robotic force environment, virtual contours of various curvatures were presented. Participants explored these contours with their hands and indicated verbally whether they could detect or discriminate between two contours. To understand what aspects of sensory or sensorimotor integration are altered by aging and disease, we manipulated the sensorimotor aspect of the task: the robot either guided the hand along the contour or the participant actively moved the hand. Active exploration relies on multimodal sensory and sensorimotor integration, while passive guidance only requires sensory integration of proprioceptive and tactile information. The main findings of the study are as follows: first, a decline in haptic precision can already be observed in adults before the age of 70 years. Parkinson’s disease may lead to an additional decrease in haptic sensitivity well beyond the levels typically seen in middle-aged and older adults. Second, the haptic deficit in Parkinson’s disease is general in nature. It becomes manifest as a decrease in sensitivity and acuity (i.e. a smaller perceivable range and a diminished ability to discriminate between two perceivable haptic stimuli). Third, thresholds during both active and passive exploration are elevated, but not significantly different from each other. That is, active exploration did not enhance the haptic deficit when compared to passive hand motion. This implies that Parkinson’s disease affects early stages of somatosensory integration that ultimately have an impact on processes of sensorimotor integration. Our results suggest that the known motor problems in Parkinson’s disease that are generally characterized as a failure of sensorimotor integration may, in fact, have a sensory origin.
Research Interests:
Sequelae in children following cerebellar tumor removal surgery are well defined, and predictors for poor recovery include lesions of the cerebellar nuclei and the inferior vermis. Dynamic reorganization is thought to promote functional... more
Sequelae in children following cerebellar tumor removal surgery are well defined, and predictors for poor recovery include lesions of the cerebellar nuclei and the inferior vermis. Dynamic reorganization is thought to promote functional recovery in particular within the first year after surgery. Yet, the time course and mechanisms of recovery within this critical time frame are elusive and longitudinal studies are missing. Thus, a group of children and adolescents (n012, range 6–17 years) were followed longitudinally after cerebellar surgery and compared to age and gender-matched controls (n011). Patients were examined (1) within the first days, (2) 3 months, and (3) 1 year after surgery. Each time behavioral tests of balance and upper limb motor function, ataxia rating, and a MRI scan were performed. Data were used for subsequent lesion–symptom mapping of cerebellar function. Behavioral improvements continued beyond 3 months, but were not complete in all patients after 1 year. At that time, remaining deficits were mild. Within the first 3 months, cerebellar lesion volumes were notably reduced by vanishing edema. Reduction in edema affecting the deep cerebellar nuclei but not reduction of total cerebellar lesion volume was a major predictor of early functional recovery. Persistent impairment in balance and upper limb function was linked to permanent lesions of the inferior vermis and the deep cerebellar nuclei.
Research Interests:
Squeri V, Sciutti A, Gori M, Masia L, Sandini G, Konczak J. Two hands, one perception: how bimanual haptic information is combined by the brain. J Neurophysiol 107: 544 –550, 2012. First published October 26, 2011;... more
Squeri V, Sciutti A, Gori M, Masia L, Sandini G, Konczak J.
Two hands, one perception: how bimanual haptic information is
combined by the brain. J Neurophysiol 107: 544 –550, 2012. First
published October 26, 2011; doi:10.1152/jn.00756.2010.—Humans
routinely use both of their hands to gather information about shape and texture of objects. Yet, the mechanisms of how the brain combines haptic information from the two hands to achieve a unified percept are unclear. This study systematically measured the haptic precision of humans exploring a virtual curved object contour with one or both hands to understand if the brain integrates haptic information from the two hemispheres. Bayesian perception theory predicts that redundant information from both hands should improve haptic estimates. Thus exploring an object with two hands should yield haptic precision that is superior to uni-manual exploration. A bimanual robotic manipulandum passively moved the hands of 20 blindfolded, right-handed adult participants along virtual curved contours. Subjects indicated which contour was more “curved” (forced choice) between two stimuli of different curvature. Contours were explored uni- or bimanually at two orientations (toward or away from the body midline). Respective psychophysical discrimination thresholds were computed. First, subjects showed a tendency for one hand to be more sensitive than the other with most of the subjects exhibiting a left-hand bias. Second, bimanual thresholds were mostly within the range of the corresponding uni-manual thresholds and were not predicted by a maximum-likelihood estimation (MLE) model. Third, bimanual curvature perception tended to be biased toward the motorically dominant hand, not toward the haptically more sensitive left hand. Two-handed exploration did not necessarily improve haptic sensitivity. We found no evidence that haptic information from both hands is integrated using a MLE mechanism. Rather, results are indicative of a process of “sensory selection”, where information from the dominant right hand is used, although the left, non-dominant hand may yield more precise haptic estimates.
Two hands, one perception: how bimanual haptic information is
combined by the brain. J Neurophysiol 107: 544 –550, 2012. First
published October 26, 2011; doi:10.1152/jn.00756.2010.—Humans
routinely use both of their hands to gather information about shape and texture of objects. Yet, the mechanisms of how the brain combines haptic information from the two hands to achieve a unified percept are unclear. This study systematically measured the haptic precision of humans exploring a virtual curved object contour with one or both hands to understand if the brain integrates haptic information from the two hemispheres. Bayesian perception theory predicts that redundant information from both hands should improve haptic estimates. Thus exploring an object with two hands should yield haptic precision that is superior to uni-manual exploration. A bimanual robotic manipulandum passively moved the hands of 20 blindfolded, right-handed adult participants along virtual curved contours. Subjects indicated which contour was more “curved” (forced choice) between two stimuli of different curvature. Contours were explored uni- or bimanually at two orientations (toward or away from the body midline). Respective psychophysical discrimination thresholds were computed. First, subjects showed a tendency for one hand to be more sensitive than the other with most of the subjects exhibiting a left-hand bias. Second, bimanual thresholds were mostly within the range of the corresponding uni-manual thresholds and were not predicted by a maximum-likelihood estimation (MLE) model. Third, bimanual curvature perception tended to be biased toward the motorically dominant hand, not toward the haptically more sensitive left hand. Two-handed exploration did not necessarily improve haptic sensitivity. We found no evidence that haptic information from both hands is integrated using a MLE mechanism. Rather, results are indicative of a process of “sensory selection”, where information from the dominant right hand is used, although the left, non-dominant hand may yield more precise haptic estimates.
Research Interests:
When looking at an object while exploring and manipulating it with the hands, visual and haptic senses provide information about the properties of the object. How these two streams of sensory information are integrated by the brain to... more
When looking at an object while exploring and manipulating it with the hands, visual and haptic senses provide information about the properties of the object. How these two streams of sensory information are integrated by the brain to form a single percept is still not fully understood. Recent advances in computational neuroscience and brain imaging research have added new insights into the underlying mechanisms and identified possible brain regions involved in visuo-haptic integration. This review examines the following main findings of previous research: First, the notion that the nervous system combines visual and haptic inputs in a fashion that minimizes the variance of the final percept and performs operations commensurable to a maximum-likelihood integrator. Second, similar to vision, haptic information may be mediated by two separate neural pathways devoted to perception and action. This claim is based on a set of psychophysical studies investigating how humans judge the size and orientation of objects. Third, a cortical neural system described as the lateral occipital complex (LOC) has been identified as a possible locus of visuo-haptic integration. This claim rests on functional imaging studies revealing an activation of LOC to both visual and haptic stimulation. We conclude that much progress has been made to provide a computational framework that can formalize and explain the results of behavioral and psychophysical studies on visuo-haptic integration. Yet, there still exists a gap between the computationally driven studies and the results derived from brain imaging studies. One reason why the closing of this gap has proven to be difficult is that visuo-haptic integration processes seem to be highly influenced by the task and context.
Research Interests:
Loss of movement coordination is the main postacute symptom after cerebellar infarction. Although the course of motor recovery has been described previously, detailed kinematic descriptions of acute stage ataxia are rare and no attempt... more
Loss of movement coordination is the main postacute symptom after cerebellar infarction. Although the course of motor recovery has been described previously, detailed kinematic descriptions of acute stage ataxia are rare and no attempt has been made to link improvements in motor function to measures of neural recovery and lesion location. This study provides a comprehensive assessment of how lesion site and arm dysfunction are associated in the acute stage and outlines the course of upper limb motor recovery for the first 4 months after the infarction.
Research Interests:
Children and young adolescents with chronic during sitting and standing in different conditions. High-surgical cerebellar lesions show persistent balance control problems during standing when lesions affect the deep cerebellar fastigial... more
Children and young adolescents with chronic during sitting and standing in different conditions. High-surgical cerebellar lesions show persistent balance control problems during standing when lesions affect the deep cerebellar fastigial and adjacent interposed nuclei. The purpose of this study is to confirm that the same lesion sites are also associated with permanent signs of trunkal ataxia during sitting. A second aim is to demonstrate that examining the postural control of patients while sitting or standing on a foam cushion may constitute a simple clinical exam yielding results commensurate to a more involved dynamic posturography exam. Balance control was assessed in 16 patients after surgery of a benign cerebellar tumor in chronic state and healthy age- and gender-matched control subjects. Using an ultrasound-based kinematic recording system, trunkal and shoulder sway was measured resolution MRI scans were acquired in the cerebellar patients. Voxel-wise statistical lesion symptom mapping was performed to compare lesioned areas between affected and unaffected patients in a given condition using χ2 tests. During sitting, 56% of cerebellar patients exhibited trunkal sway outside the range of healthy controls, and 87.5% of cerebellar patients revealed abnormal sway patterns during standing. Abnormalities were most pronounced when visual information was absent, and somatosensory information became unreliable and/or when the base of support along the medio-lateral axis was minimized during tandem stance. Lesion symptom mapping revealed that pathological values in the behavior data were more likely in patients with surgical lesions involving the fastigial nuclei (NF) and adjacent interposed nuclei (NI). In patients with surgery <1-year lesions of the inferior cerebellar vermis also had an impact on balance function. Our results corroborate previous evidence that the extent of permanent damage to the deep cerebellar nuclei greatly impacts on the recovery on balance function.
Research Interests:
The parietal lobe is part of a sensory system comprising peripheral receptors, neural pathways, and neurons of several supraspinal centers (cerebellum, basal ganglia, parietal lobe) that process visual and somatosensory information. The... more
The parietal lobe is part of a sensory system comprising peripheral receptors, neural pathways, and neurons of several supraspinal centers (cerebellum, basal ganglia, parietal lobe) that process visual and somatosensory information. The somatosensory modalities include proprioception (e.g., perception of body and limb positions), interoceptive sensory modalities such as temperature and pain perception, and touch. Classically, touch has been defined as an exteroceptive sense. However, in recognition that touch perception is based on several modalities, the term somatic senses is also commonly used. It is known that the parietal lobes mediate exteroceptive and proprioceptive perception, while interoceptive sensations are also associated with activations of the right insular cortex. This article will focus primarily on the parietal lobe, and the effect of parietal lobe lesions on cognitive, perceptual, and motor function. One of the primary roles of the parietal cortex lies in the integration of somatosensory and visual information that is needed for movement planning and control. In addition, specific areas of the parietal lobe are relevant for cognitive processes such as reading comprehension, and logical and mathematical thinking. One of the first comprehensive accounts of parietal lobe function was published in 1953 by the British neurologist Macdonald Critchley whose insights were based largely on the study of patients with parietal lesions. Since then, numerous researchers attempted to correlate behaviors with parietal and subcortical neural activity in humans and animals using an array of psychophysical, electrophysiological, and brain imaging techniques.
Research Interests:
Increasing evidence indicates that processing of proprioceptive information is altered in Parkinson’s disease(PD), leading to reduced kinaesthetic and haptic sensitivity.However, there is inconclusive evidence whether dopamine replacement... more
Increasing evidence indicates that processing of proprioceptive information is altered in Parkinson’s disease(PD), leading to reduced kinaesthetic and haptic sensitivity.However, there is inconclusive evidence whether dopamine replacement therapy (DRT) ameliorates or worsens kin-aesthetic and haptic function in PD. For assessing perceptual function, we employed a task that did not require active motion or stressed working memory function, which may become impaired in PD. A group of mild to moderate stage PD patients (n=9) and a group of age matched healthy controls participated in this study. Without vision, a subject’s hand was moved by a robotic manipulandum along the contours of a small ‘‘virtual box’’ (5 x 15 cm). At the end of each trial, they indicated whether the contour was ‘‘curved’’ or ‘‘straight’’. PD patients were tested ON and OFF antiparkinsonian medication. Psychophysical detection thresholds were determined (curvature at which subjects correctly perceived a curved contour at the 75% level). Compared to the control group, thresholds were elevated by 55% in the PD patient group. During the ON medication state, the mean detection threshold of the patient group was reduced by 15% (ON: 4.71 m-1; OFF: 5.42 m-1). Increases in curvature sensitivity were highly correlated with improved clinical scores of motor function(r = 0.74) with more affected patients showing higher gains in sensitivity as the result of DRT (r = 0.80). This report documents that DRT can ameliorate haptic and kinaesthetic function in patients with mild to moderate PD, suggesting that DRT can have beneficial effects on perceptual function.
Research Interests:
Parkinson's disease (PD) is a neurogenerative disorder that leads to a progressive decline in motor function. Growing evidence indicates that PD patients also experience an array of sensory problems that negatively impact motor function.... more
Parkinson's disease (PD) is a neurogenerative disorder that leads to a progressive decline in motor function. Growing evidence indicates that PD patients also experience an array of sensory problems that negatively impact motor function. This is especially true for proprioceptive deficits, which profoundly degrade motor performance. This review specifically address the relation between proprioception and motor impairments in PD. It is structured around 4 themes: (a) It examines whether the sensitivity of kinaesthetic perception, which is based on proprioceptive inputs, is actually altered in Pd. (b) It discusses whether failed processes of proprioceptive-motor integration are central to the motor problems in PD. (c) It presents recent findings focusing on the link between the proprioception and the balance problems in Pd. And (d) it discusses the current state of knowledge of how levodopa medication and deep brain stimulation affect proprioceptive and motor function in PD. The authors conclude that a failure to evaluate and to map proprioceptive information onto voluntary and reflexive motor commands is an integral part of the observed motor symptoms in PD.
Research Interests:
Playing a violin requires precise patterns of limb coordination that are acquired over years of practice. In the present study, the authors investigated how motion at proximal arm joints influenced the precision of bow movements in novice... more
Playing a violin requires precise patterns of limb coordination that are acquired over years of practice. In the present study, the authors investigated how motion at proximal arm joints influenced the precision of bow movements in novice learners and experts. The authors evaluated the performances of 11 children (4–12 years old), 3 beginning-to-advanced level adult players, and 2 adult concert violinists, using a musical work that all had mastered as their first violin piece. The authors found that learning to play the violin was not associated with a release or freeing of joint degrees of freedom. Instead, learning was characterized by an experience-dependent suppression of sagittal shoulder motion, as documented by an observed reduction in joint angular amplitude. This reduction in the amplitude of shoulder flexion–extension correlated highly with a decrease of bow-movement variability. The remaining mechanical degrees of freedom at the elbow and shoulder showed patterns of neither suppression nor freeing. Only violinists with more than 700 practice hr achieved sagittal shoulder range of motion comparable to experts. The findings imply that restricting joint amplitude at selected joint degrees of freedom, while leaving other degrees of freedom unconstrained, constitutes an appropriate strategy for learning complex, high-precision motor patterns in children and adults. The findings also highlight that mastering even seemingly simple bowing movements constitutes a prolonged learning process.
Research Interests:
The pathogenesis of essential tremor (ET) is still under debate. Several lines of evidence indicate that ET is associated with cerebellar dysfunction. The aim of the present study was to find corroborating evidence for this claim by... more
The pathogenesis of essential tremor (ET) is still under debate. Several lines of evidence indicate that ET is associated with cerebellar dysfunction. The aim of the present study was to find corroborating evidence for this claim by investigating balance and speech impairments in patients with ET. In addition, the effect of deep brain stimulation (DBS) on balance and speech function was studied. A group of 25 ET patients including 18 with postural and/or simple kinetic tremor (ETpt) and seven ET patients with additional clinical signs of cerebellar dysfunction (ETc) was compared to 25 healthy controls. In addition, 12 ET patients with thalamic DBS participated in the study. Balance control was assessed during gait and stance including tandem gait performed on a treadmill as well as static and dynamic posturography. Motor speech control was analyzed through syllable repetition tasks. Signs of balance impairment were found in early stages and advanced stages of ET. During locomotion, ET patients exhibited an increased number of missteps and shortened stride length with tandem gait. ETc patients and, to a lesser extent, ETpt patients had increased postural instability in dynamic posturography conditions that are sensitive to vestibular or vestibulocerebellar dysfunction. ETc but not ETpt patients exhibited significantly increased syllable durations. DBS had no discernable effect on speech performance or balance control. We conclude that the deficits in balance as well as the subclinical signs of dysarthria in a subset of patients confirm and extend previous findings that ET is associated with an impairment
of the cerebellum.
of the cerebellum.
Research Interests:
The first reaching movements of human infants lack limb coordination leading to ataxic like hand trajectories. Kinematically, these early trajectories are characterized by multiple peaks in the hand velocity profile which gradually... more
The first reaching movements of human infants lack limb coordination leading to ataxic like hand trajectories. Kinematically, these early trajectories are characterized by multiple peaks in the hand velocity profile which gradually decrease in frequency during development. In this paper we explore the hypothesis that the jerky hand trajectories seen in early infancy can be the result of imprecise internal motor models. Results from our simulation suggest that imprecise estimations of multi-joint inter-segmental torques (e.g.,Coriolis forces) by the controller may induce multi-peak hand velocity profiles. When the system was allowed to use delayed peripheral feedback (300 ms after reaching onset), the resulting kinematics began to resemble those seen in early infancy. This suggests that the output of an imprecise internal model of limb dynamics coupled with delayed feedback maybe sufficient to explain early human hand trajectories. Our data provide an alternative to previous hypotheses theorizing jerky trajectories as the result of concatenated mini ballistic movements.
Research Interests:
This study presents a method to quantify a child’s sensitivity to passive limb motion, which is an important aspect of kinaesthesia not easily examined clinically. Psychophysical detection thresholds to passive forearm motion were... more
This study presents a method to quantify a child’s sensitivity to passive limb motion, which is an important aspect of kinaesthesia not easily examined clinically. Psychophysical detection thresholds to passive forearm motion were determined in a group of 20 typically developing pre-adolescent children (mean age 12y 6mo, SD 10mo, range 11)13y) and a group of 10 healthy adults (mean age 29y 10mo, SD 10y 7mo, range 18)50y). A newly designed passive motion apparatus was used to measure the time to detection of forearm motion and the errors in determining movement direction. Results showed that limb motion sensitivity became increasingly variable below 0.3 degrees/s in children and adults. In comparison with adults, movement detection times in the pediatric group were increased by between 4 and 108% for the range of tested velocities (0.075)1.35 ⁄ s). At 0.075 ⁄ s, 5% of the children, but 50% of the adults, made no directional error, indicating that motion perception became unreliable at such low velocity in both groups. The findings demonstrate that sensitivity to passive forearm motion in children should be tested at a range between 0.075 and 0.3 ⁄ s. They further suggest that passive motion sensitivity may not be fully developed in pre-adolescent children.
Research Interests:
Haptic perception is based on the integration of afferent proprioceptive and tactile signals. A further potential source of information during active touch is predicted sensory feedback (PSF) derived from a copy of efferent motor commands... more
Haptic perception is based on the integration of afferent proprioceptive and tactile signals. A further potential source of information during active touch is predicted sensory feedback (PSF) derived from a copy of efferent motor commands that give rise to the exploratory actions. There is substantial evidence that PSF is important for predicting the sensory consequences of action, but its role in perception is unknown. Theoretically, PSF leads to a higher redundancy of haptic information, which should improve sensitivity of the haptic sense. To investigate the effect of PSF on haptic precision, blindfolded subjects haptically explored the curved contour of a virtual object generated by a robotic manipulandum. They either actively moved their hand along the contour, or their hand was moved passively by the device along the same contour. In the active condition afferent sensory information and PSF were present, while in the passive condition subjects relied solely on afferent information. In each trial, two stimuli of different curvature were presented. Subjects needed to
indicate which of the two was more ‘‘curved’’ (forced choice). For each condition, the detection and three dis- crimination thresholds were computed. The main finding is that absence of efference copy information did not systematically degrade haptic acuity. This indirectly implies that PSF does not aid or enhance haptic perception. We conclude that when maximum haptic sensitivity is required to explore novel objects, the perceptual system relies primarily on afferent tactile and proprioceptive information, and PSF has no added effect on the precision of the perceptual estimate.
indicate which of the two was more ‘‘curved’’ (forced choice). For each condition, the detection and three dis- crimination thresholds were computed. The main finding is that absence of efference copy information did not systematically degrade haptic acuity. This indirectly implies that PSF does not aid or enhance haptic perception. We conclude that when maximum haptic sensitivity is required to explore novel objects, the perceptual system relies primarily on afferent tactile and proprioceptive information, and PSF has no added effect on the precision of the perceptual estimate.
Research Interests:
While high-resolution structural magnetic resonance imaging (MRI) combined with newer analysis methods has become a powerful tool in human cerebral lesion studies, comparatively few studies have used these advanced imaging techniques to... more
While high-resolution structural magnetic resonance imaging (MRI) combined with newer analysis methods has become a powerful tool in human cerebral lesion studies, comparatively few studies have used these advanced imaging techniques to study lesions of the human cerebellum and their associated symptoms. This review will summarize the
methodology of MRI-based lesion-symptom mapping of the human cerebellum and discuss its potential for gaining insights into cerebellar function. The investigation of patients with defined focal lesions yields the greatest potential for obtaining meaningful correlations between lesion site and behavioral deficits. In smaller groups of patients overlay plots and subtraction analysis are good options. If larger groups of patients are available, different statistical techniques have been introduced to compare behavior and lesion site on a voxel-by-voxel basis. Although localization in degenerative cerebellar disorders is less accurate because of the diffuse nature of the disease, certain information about the supposed function of larger subdivisions of the cerebellum can be gained. Examples are given which show that lesion-symptom mapping allows to investigate the function of the intermediate zone and cerebellar nuclei. We conclude that meaningful correlations between lesion site and behavioral data can be obtained in patients with degenerative as well as focal cerebellar disorders.
methodology of MRI-based lesion-symptom mapping of the human cerebellum and discuss its potential for gaining insights into cerebellar function. The investigation of patients with defined focal lesions yields the greatest potential for obtaining meaningful correlations between lesion site and behavioral deficits. In smaller groups of patients overlay plots and subtraction analysis are good options. If larger groups of patients are available, different statistical techniques have been introduced to compare behavior and lesion site on a voxel-by-voxel basis. Although localization in degenerative cerebellar disorders is less accurate because of the diffuse nature of the disease, certain information about the supposed function of larger subdivisions of the cerebellum can be gained. Examples are given which show that lesion-symptom mapping allows to investigate the function of the intermediate zone and cerebellar nuclei. We conclude that meaningful correlations between lesion site and behavioral data can be obtained in patients with degenerative as well as focal cerebellar disorders.
Research Interests:
Parkinson’s disease (PD) is a neurodegenerative disorder that leads to a progressive decline in motor function. Growing evidence indicates that PD patients also experience an array of sensory problems that negatively impact motor... more
Parkinson’s disease (PD) is a neurodegenerative disorder
that leads to a progressive decline in motor function. Growing
evidence indicates that PD patients also experience an array of
sensory problems that negatively impact motor function. This is especially true for proprioceptive deficits, which profoundly degrade motor performance. This review specifically address the relation between proprioception and motor impairments in PD. It is structured around 4 themes: (a) It examines whether the sensitivity of kinaesthetic perception, which is based on proprioceptive inputs, is actually altered in PD. (b) It discusses whether failed processes of proprioceptive-motor integration are central to the motor problems in PD. (c) It presents recent findings focusing on the link between the proprioception and the balance problems in PD. And (d) it discusses the current state of knowledge of how levodopa medication and deep brain stimulation affect proprioceptive and motor function in PD. The authors conclude that a failure to evaluate and to map proprioceptive information onto voluntary and reflexive motor commands is an integral part of the observed motor symptoms in PD.
that leads to a progressive decline in motor function. Growing
evidence indicates that PD patients also experience an array of
sensory problems that negatively impact motor function. This is especially true for proprioceptive deficits, which profoundly degrade motor performance. This review specifically address the relation between proprioception and motor impairments in PD. It is structured around 4 themes: (a) It examines whether the sensitivity of kinaesthetic perception, which is based on proprioceptive inputs, is actually altered in PD. (b) It discusses whether failed processes of proprioceptive-motor integration are central to the motor problems in PD. (c) It presents recent findings focusing on the link between the proprioception and the balance problems in PD. And (d) it discusses the current state of knowledge of how levodopa medication and deep brain stimulation affect proprioceptive and motor function in PD. The authors conclude that a failure to evaluate and to map proprioceptive information onto voluntary and reflexive motor commands is an integral part of the observed motor symptoms in PD.
Research Interests:
While high-resolution structural magnetic resonance imaging (MRI) combined with newer analysis methods has become a powerful tool in human cerebral lesion studies, comparatively few studies have used these advanced imaging techniques to... more
While high-resolution structural magnetic resonance imaging (MRI) combined with newer analysis methods has become a powerful tool in human cerebral lesion studies, comparatively few studies have used these advanced imaging techniques to study lesions of the human cerebellum and their associated symptoms. This review will summarize the methodology of MRI-based lesion-symptom mapping of the human cerebellum and discuss its potential for gaining insights into cerebellar function. The investigation of patients with defined focal lesions yields the greatest potential for obtaining meaningful correlations between lesion site and behavioral deficits. In smaller groups of patients overlay plots and subtraction analysis are good options. If larger groups of patients are available, different statistical techniques have been introduced to compare behavior and lesion site on a voxel-by-voxel basis. Although localization in degenerative cerebellar disorders is less accurate because of the diffuse nature of the disease, certain information about the supposed function of larger subdivisions of the cerebellum can be gained. Examples are given which show that lesion-symptom mapping allows to investigate the function of the intermediate zone and cerebellar nuclei. We conclude that meaningful correlations between lesion site and behavioral data can be obtained in patients with degenerative as well as focal cerebellar disorders.
Research Interests:
Up to 50% of children and adolescents with attention deficit/hyperactivity disorder (ADHD) exhibit motor abnormalities including altered balance. Results from brain imaging studies indicate that these balance deficits could be of... more
Up to 50% of children and adolescents with attention deficit/hyperactivity disorder (ADHD) exhibit motor abnormalities including altered balance. Results from brain imaging studies indicate that these balance deficits could be of cerebellar origin as ADHD children may show atrophy in those regions of the cerebellum associated with gait and balance control. To address this question, this study investigated postural and gait abilities in ADHD children and compared their static and dynamic balance with children with known lesions in the cerebellum. Children diagnosed with ADHD according to DSM IV-TR diagnostic criteria were compared with children with chronic surgical cerebellar lesions and age-matched controls. A movement coordination test was used to assess differences in motor development. Postural and gait abilities were assessed using posturography, treadmill walking and a paced stepping task. Volumes of the cerebellum and the cerebrum were assessed on the basis of 3D magnetic resonance images (MRI). Children with cerebellar lesions showed significant performance decrements in all tasks compared with the controls, particularly in the movement coordination test and paced stepping task. During dynamic posturography ADHD-participants showed mild balance problems which correlated with findings in cerebellar children. ADHD children showed abnormalities in a backward walking task and minor abnormalities in the paced stepping test. They did not differ in treadmill walking from the controls. These findings support the notion that cerebellar dysfunction may contribute to the postural deficits seen in ADHD children. However, the observed abnormalities were minor. It needs to be examined whether balance problems become more pronounced in ADHD children exhibiting more prominent signs of clumsiness.
Research Interests:
Up to 50% of children and adolescents with attention deficit/hyperactivity disorder (ADHD) exhibit motor abnormalities including altered balance. Results from brain imaging studies indicate that these balance deficits could be of... more
Up to 50% of children and adolescents with attention deficit/hyperactivity disorder (ADHD) exhibit motor abnormalities including altered balance. Results from brain imaging studies indicate that these balance deficits could be of cerebellar origin as ADHD children may show atrophy in those regions of the cerebellum associated with gait and balance control. To address this question, this study investigated postural and gait abilities in ADHD children and compared their static and dynamic balance with children with known lesions in the cerebellum. Children diagnosed with ADHD according to DSM IV-TR diagnostic criteria were compared with children with chronic surgical cerebellar lesions and age-matched controls. A movement coordination test was used to assess differences in motor development. Postural and gait abilities were assessed using posturography, treadmill walking and a paced stepping task. Volumes of the cerebellum and the cerebrum were assessed on the basis of 3D magnetic resonance images (MRI). Children with cerebellar lesions showed significant performance decrements in all tasks compared with the controls, particularly in the movement coordination test and paced stepping task. During dynamic posturography ADHD-participants showed mild balance problems which correlated with findings in cerebellar children. ADHD children showed abnormalities in a backward walking task and minor abnormalities in the paced stepping test. They did not differ in treadmill walking from the controls. These findings support the notion that cerebellar dysfunction may contribute to the postural deficits seen in ADHD children. However, the observed abnormalities were minor. It needs to be examined whether balance problems become more pronounced in ADHD children exhibiting more prominent signs of clumsiness.
Research Interests:
The haptic perception of the curvature of an object is essential for adequate object manipulation and critical for our guidance of actions. This study investigated how the ability to perceive the curvature of an object is altered by... more
The haptic perception of the curvature of an object is essential for adequate object manipulation and critical for our guidance of actions. This study investigated how the ability to perceive the curvature of an object is altered by Parkinson’s disease (PD).
Eight healthy subjects and 11 patients with mild to moderate PD had to judge, without vision, the curvature of a virtual ‘‘box’’ created by a robotic manipulandum. Their hands were either moved passively along a defined curved path or they actively explored the curved curvature of a virtual wall. The curvature was either concave or convex (bulging to the left or right) and was judged in two locations of the hand workspace–a left workspace location, where the curved hand path was associated with curved shoulder and elbow joint paths, and a right workspace location in which these joint paths were nearly linear. After exploring the curvature of the virtual object, subjects had to judge whether the curvature was concave or convex. Based on these data, thresholds for curvature sensitivity were established. The main findings of the study are: First, 9 out 11 PD patients (82%) showed elevated thresholds for detecting convex curvatures in at least one test condition. The respective median threshold for the PD group was increased by 343% when compared to the control group. Second, when distal hand paths became less associated with proximal joint paths (right workspace), haptic acuity was reduced substantially in both groups. Third, sensitivity to hand trajectory curvature was not improved during active exploration in either group.
Our data demonstrate that PD is associated with a decreased acuity of the haptic sense, which may occur already at an early stage of the disease.
Eight healthy subjects and 11 patients with mild to moderate PD had to judge, without vision, the curvature of a virtual ‘‘box’’ created by a robotic manipulandum. Their hands were either moved passively along a defined curved path or they actively explored the curved curvature of a virtual wall. The curvature was either concave or convex (bulging to the left or right) and was judged in two locations of the hand workspace–a left workspace location, where the curved hand path was associated with curved shoulder and elbow joint paths, and a right workspace location in which these joint paths were nearly linear. After exploring the curvature of the virtual object, subjects had to judge whether the curvature was concave or convex. Based on these data, thresholds for curvature sensitivity were established. The main findings of the study are: First, 9 out 11 PD patients (82%) showed elevated thresholds for detecting convex curvatures in at least one test condition. The respective median threshold for the PD group was increased by 343% when compared to the control group. Second, when distal hand paths became less associated with proximal joint paths (right workspace), haptic acuity was reduced substantially in both groups. Third, sensitivity to hand trajectory curvature was not improved during active exploration in either group.
Our data demonstrate that PD is associated with a decreased acuity of the haptic sense, which may occur already at an early stage of the disease.
Research Interests:
High-resolution structural magnetic resonance imaging (MRI) has become a powerful tool in human cerebellar lesion studies. Structural MRI is helpful to analyse the localisation and extent of cerebellar lesions and to determine possible... more
High-resolution structural magnetic resonance imaging (MRI) has become a powerful tool in human cerebellar lesion studies. Structural MRI is helpful to analyse the localisation and extent of cerebellar lesions and to determine possible extracerebellar involvement. Functionally meaningful correlations between a cerebellar lesion site and behavioral data can be obtained both in subjects with degenerative as well as focal cerebellar disorders. In this review, examples are presented which demonstrate that MRI-based lesion-symptom mapping is helpful to study the function of cerebellar cortex and cerebellar nuclei. Behavioral measures were used which represent two main areas of cerebellar function, that is, motor coordination and motor learning. One example are correlations with clinical data which are in good accordance with the known functional compartmentalisation of the cerebellum in three sagittal zones: In patients with cerebellar cortical degeneration ataxia of stance and gait was correlated with atrophy of the medial (and intermediate) cerebellum, oculomotor disorders with the medial, dysarthria with the intermediate and limb ataxia with atrophy of the intermediate and lateral cerebellum. Similar findings were obtained in patients with focal lesions. In addition, in patients with acute focal lesions, a somatotopy in the superior cerebellar cortex was found which is in close relationship to animal data and functional MRI data in healthy control subjects. Finally, comparison of data in patients with acute and chronic focal lesions revealed that lesion site appears to be critical for motor recovery. Recovery after lesions to the nuclei of the cerebellum was less complete. Another example which extended knowledge about functional localisation within the cerebellum is classical conditioning of the eyeblink response, a simple form of motor learning. In healthy subjects, learning rate was related to the volume of the cortex of the posterior cerebellar love. In patients with focal cerebellar lesions, acquisition of eyeblink conditioning was significantly reduced in lesions including the cortex of the superior posterior lobe, but not the inferior posterior lobe. disorder timing of conditioned eyeblink responses correlated with lesions of the anterior lobe. Findings are in good agreement with the animal literature. different parts of the cerebellar cortex may be involved in acquisition and timing of conditioned eyeblink responses in humans. These examples demonstrate that MRI-based lesion-symptom mapping is helpful to study the contribution of functionally relevant cerebellar compartments in motor control and recovery in patients with cerebellar disease. In addition, information about the function of cerebellar cortex and nuclei can be gained.
Research Interests:
The perception of limb motion is a kinaesthetic property that is essential for voluntary motor control. This study examined the ability of patients with Parkinson's disease (PD) to detect the velocity o a passively moved limb. Eight... more
The perception of limb motion is a kinaesthetic property that is essential for voluntary motor control. This study examined the ability of patients with Parkinson's disease (PD) to detect the velocity o a passively moved limb. Eight patients with mild to moderate PD and eight age-matched healthy controls participated. They placed their forearm on a padded splint of a passive motion apparatus, which horizontally extended or flexed the elbow joint at velocities between 1.65 and 0.075 degrees/second (in steps of 0.15 degrees/second). Passive movement persisted until subjects detected arm motion and pressed a trigger held in the hand of their non-tested arm. Time until detection and associated arm displacement were recorded and subsequently adjusted for each subject's reaction time. We found that PD patients need significantly larger limb displacements before they could judge the presence of passive motion. With decreasing passive motion velocity the detection time increased exponentially in both groups. Yet, the mean detection times of the PD group were 92-166% higher than in the control group for each of the 12 tested velocity conditions. Five of the eight patients were on Parkinsonian medication when tested. Yet, the degree of impairment did not correlate significantly with the patients' levodopa equivalent dosage. Our results demonstrate that PD patients were impaired in the detection of passive forearm movements. This study complements a growing body of evidence indicating that various aspects of kinaesthesis (position sense, weight perception, passive motion sense) are affected event at early stages of PD. The impaired processing of proprioceptive signals likely contributes to motor symptoms in PD.
Research Interests:
This review provides a developmental perspective on our current understanding of the role of the cerebellum for sensorimotor and cognitive function. A synopsis on the contribution of the cerebellum on motor control, learning and cognition... more
This review provides a developmental perspective on our current understanding of the role of the cerebellum for sensorimotor and cognitive function. A synopsis on the contribution of the cerebellum on motor control, learning and cognition based on experiments in human adults and animals is presented. This knowledge is contrasted to the relevant literature on children and adolescents. Special attention is given to findings derived from lesion studies and clinical reports that examined the effect of cerebellar damage during development. In general, it is established that children may show the same sensorimotor deficits as adults as a result of cerebellar damage, while the findings of cognitive dysfunction in children are less clear and remain controversial. Younger children do not necessarily recover better than older children or adolescents. The sparing of the deep cerebellar nuclei and the extent of adjuvant chemo or radiation therapy are better predictors of later motor and cognitive function in children and adolescents.
Research Interests:
With head movement, suppression of vestibular inputs during visual exploration is necessary not only for reorienting gaze, but also to direct attention to new visual targets. People with progressive supranuclear palsy (PSP) have... more
With head movement, suppression of vestibular inputs during visual exploration is necessary not only for reorienting gaze, but also to direct attention to new visual targets. People with progressive supranuclear palsy (PSP) have difficulty suppressing the vestibuloocular reflex (VOR) and it was hypothesized that the magnitude of VOR suppression deficit correlates with the degree of degradation of attention and visuospatial performance. We evaluated cognitive and visuo-motor function in 8 subjects with PSP (4 men and 4 women; ages 59 – 83 years). Gaze control was studied by measuring the accuracy of eye– head coordination during passive vertical and horizontal head-on-trunk movements. Fixation was assessed when subjects viewed either an earth-fixed or head-fixed target. A gaze fixation score (GFS) was calculated to represent the amount of error between eye and head movement in each plane (eye– head root mean square error normalized to the range of head rotation). The vertical but not horizontal GFS during attempted suppression of the VOR was significantly related to attention (r 0.70; P 0.05) and visuospatial ability (r 0.76; P 0.03). These findings suggest that the ability to suppress the VOR during vertical smooth movements of the head is associated with the magnitude of cognitive deficit in PSP.
Research Interests:
This article was originally published in a journal published by Elsevier, and the attached copy is provided by Elsevier for the author's benefit and for the benefit of the author's institution, for non-commercial research and educational... more
This article was originally published in a journal published by Elsevier, and the attached copy is provided by Elsevier for the author's benefit and for the benefit of the author's institution, for non-commercial research and educational use including without limitation use in instruction at your institution, sending it to specific colleagues that you know, and providing a copy to your institution's administrator. All other uses, reproduction and distribution, including without limitation commercial reprints, selling or licensing copies or access, or posting on open internet sites, your personal or institution's website or repository, are prohibited. For exceptions, permission may be sought for such use through Elsevier's permissions site at: http://www.elsevier.com/locate/permissionusematerial Abstract To investigate the processing of linear perspective and binocular information for action and for the perceptual judgment of depth, we presented viewers with an actual Ames trapezoidal window. The display, when presented perpendicular to the line of sight, provided perspective information for a rectangular window slanted in depth, while binocular information specified a planar surface in the fronto-parallel plane. We compared pointing towards the display-edges with perceptual judgment of their positions in depth as the display orientation was varied under monocular and binocular view. On monocular trials, pointing and depth judgment were based on the perspective information and failed to respond accurately to changes in display orientation because pictorial information did not vary sufficiently to specify the small differences in orientation. For binocular trials, pointing was based on binocular information and precisely matched the changes in display orientation whereas depth judgment was short of such adjustment and based upon both binocular and perspective-specified slant information. The finding, that on binocular trials pointing was considerably less responsive to the illusion than perceptual judgment, supports an account of two separate processing streams in the human visual system, a ventral pathway involved in object recognition and a dorsal pathway that produces visual information for the control of actions. Previously, similar differences between perception and action were explained by an alternate explanation, that is, viewers selectively attend to different parts of a display in the two tasks. The finding that under monocular view participants responded to perspective information in both the action and the perception task rules out the attention-based argument. Published by Elsevier Ltd.
Research Interests:
There is increasing evidence that the cerebellum and the basal ganglia serve not only a role in motor control but also in visual perception. Patients with Parkinson’s disease (PD) as well as patients with cerebellar lesions exhibit... more
There is increasing evidence that the cerebellum and the basal ganglia serve not only a role in motor control but also in visual perception. Patients with Parkinson’s disease (PD) as well as patients with cerebellar lesions exhibit impairments of vision that are not fully explained by ocular motor deficits. It is less clear to which extent these visual deficits contribute to an impaired control of visually guided movements. This study examined whether a dysfunction of the cerebellum or the basal ganglia induces impairments in depth perception, which affect action. We employed an illusionary display, the Ames trapezoidal window, to determine the ability of PD patients (n=10) and patients with spinocerebellar ataxia (SCA) (n=6) to process depth cues when estimating object slant. Participants either pointed to the edges of the window (motor judgement) or verbally indicated the perceived orientation of the display (verbal judgement). To control for ocular and limb motor deficits, participants judged the slant of a non-illusionary display in a second task. Slant estimation of the non-illusionary window was not impaired in either patient group when compared to control subjects (all P>0.2). In contrast, SCA as well as PD patients exhibited significantly greater slant estimation errors than controls when pointing to the illusionary window (P=0.005). In addition, both patient groups made larger errors than controls in their verbal judgements during binocular viewing of the illusion (P=0.005), but not during monocular viewing (P>0.2). In sum, the present findings point towards a role for both the basal ganglia and cerebellum for the processing of visual information about depth. Since the deficits were seen both in the context of action and perception and were only partially reconciled by the availability of binocular depth cues, we conclude that basal ganglia as well as cerebellar disease may affect the visual perception of depth.
Research Interests:
The present study investigated whether a specific aspect of proprioception, the sense of heaviness or weight is affected in PD. We determined detection thresholds for the perception of a gravito-inertial load in 10 PD patients and 11... more
The present study investigated whether a specific aspect of proprioception, the sense of heaviness or weight is affected in PD. We determined detection thresholds for the perception of a gravito-inertial load in 10 PD patients and 11 age-matched control subjects. A gradually increasing weight
was applied to the index finger by means of two slings of different width (low vs. high skin pressure). For the controls, mean detection thresholds were 31.3 g at skin high pressure and
33.0 g under low pressure. PD patients revealed significantly higher thresholds than the control group in both pressure conditions (mean high pressure,47.7 g; mean low pressure, 52.3 g; group effect, P 0.001). Thresholds of PD patients tended to increase with disease severity as measured by the Unified Parkinson’s Disease Rating Scale Motor score (r 0.55) but did not correlate significantly with levodopa equivalent dosage. The results demonstrate that the perception of heaviness or weight is already affected in the early stages of PD. These findings underline the growing evidence that proprioceptive and possibly haptic dysfunction is a common feature of PD.
was applied to the index finger by means of two slings of different width (low vs. high skin pressure). For the controls, mean detection thresholds were 31.3 g at skin high pressure and
33.0 g under low pressure. PD patients revealed significantly higher thresholds than the control group in both pressure conditions (mean high pressure,47.7 g; mean low pressure, 52.3 g; group effect, P 0.001). Thresholds of PD patients tended to increase with disease severity as measured by the Unified Parkinson’s Disease Rating Scale Motor score (r 0.55) but did not correlate significantly with levodopa equivalent dosage. The results demonstrate that the perception of heaviness or weight is already affected in the early stages of PD. These findings underline the growing evidence that proprioceptive and possibly haptic dysfunction is a common feature of PD.
Research Interests:
Parkinson’s disease (PD) and focal dystonia (FD) are both predominantly characterized by motor symptoms. Also, recent research has shown that sensory processing is impaired in both movement disorders. FD is characterized by involuntary... more
Parkinson’s disease (PD) and focal dystonia (FD) are both predominantly characterized by motor symptoms. Also, recent research has shown that sensory processing is impaired in both movement disorders. FD is characterized by involuntary movements and abnormal limb postures; thus, abnormal kinesthesia could be involved in the pathogenesis. We examined passive index finger movements in patients with FD (n 12) and PD (n 11) and in age-matched healthy controls (n 13). Compared to healthy controls, patients with PD and FD were significantly impaired in the correct detection of the movement direction. The perceptual thresholds for 75% correct responses of movement direction were 0.21 degrees for FD and 0.28 degrees for PD patients compared to 0.13 degrees in control subjects. Subjects with PD and FD were also significantly impaired when they had to judge consecutive amplitudes. Results of the present study point to impaired kinesthesia in FD. Defective sensory processing could be involved in the pathophysiology of the disease and may influence dystonic contractions.
Research Interests:
The perception of limb motion is a kinaesthetic property that is essential for voluntary motor control. This study examined the ability of patients with Parkinson’s disease (PD) to detect the velocity of a passively moved limb. Eight... more
The perception of limb motion is a kinaesthetic property that is essential for voluntary motor control. This study examined the ability of patients with Parkinson’s disease (PD) to detect the velocity of a passively moved limb. Eight patients with mild to moderate PD and eight age-matched healthy controls participated. They placed their forearm on a padded splint of a passive motion apparatus, which horizontally extended or flexed the elbow joint at velocities between 1.65 and 0.075/s (in steps of 0.15/s). Passive movement persisted until subjects detected arm motion and pressed a trigger held in the hand of their non-tested arm. Time until detection and associated arm displacement were recorded and subsequently adjusted for each subject’s reaction time. We found that PD patients needed significantly larger limb displacements before they could judge the presence of passive motion. With decreasing passive motion velocity the detection time increased exponentially in both groups. Yet, the mean detection times of the PD group were 92–166% higher than in the control group for each of the 12 tested velocity conditions. Five of the eight patients were on Parkinsonian medication when tested. Yet,the degree of impairment in the PD group did not correlate significantly with the patients’ levodopa equivalent dosage. Our results demonstrate that PD patients were impaired in the detection of passive fore arm movements. This study compliments a growing body of evidence indicating that various aspects of kinaesthesis (position sense,weight perception, passive motion sense) are affected even at early stages of PD. The impaired processing of proprioceptive signals likely contributes to motor symptoms in PD.
Research Interests:
This study examined whether lesions to the cerebellum obtained in early childhood are better compensated than lesions in middle childhood or adolescence. Since cerebellar lesions might affect motor as well a cognitive performance,... more
This study examined whether lesions to the cerebellum obtained in early childhood are better compensated than lesions in middle childhood or adolescence. Since cerebellar lesions might affect motor as well a cognitive performance, posture, upper limb and working memory function were assessed in 22 patients after resection of a cerebellar tumour (age at surgery 1–17 years, minimum 3 years post-surgery). Working memory was only impaired in those patients who had received chemo- or radiation therapy. Postural sway was enhanced in 64% of the patients during dynamic posturography conditions, which relied heavily on vestibular input for equilibrium control. Upper limb function was generally less impaired, but 54% of the patients revealed prolonged deceleration times in an arm pointing task, which probably does not reflect a genuine cerebellar deficit but rather the patients’ adopted strategy to avoid overshooting. Age at surgery, time since surgery or lesion volume were poor predictors of motor or cognitive recovery. Brain imaging analysis revealed that lesions of all eight patients with abnormal posture who did not receive chemo- and/or radiation therapy included the fastigial and interposed nuclei (NF and NI). In patients with normal posture, NI and NF were spared. In 11 out of 12 patients with abnormal deceleration time, the region with the highest overlap included the NI and NF and dorsomedial portions of the dentate nuclei in 10 out of 12 patients. We conclude that cerebellar damage inflicted at a young age is not necessarily better compensated. The lesion site is critical for motor recovery, and lesions affecting the deep cerebellar nuclei are not fully compensated at any developmental age in humans.
Research Interests:
This article reviews to reflexive motor patterns in humans: Primitive reflexes and motor primitives. Both terms coexist in the literature of motor development and motor control yet they are not synonyms. While primitive reflexes are a... more
This article reviews to reflexive motor patterns in humans: Primitive reflexes and motor primitives. Both terms coexist in the literature of motor development and motor control yet they are not synonyms. While primitive reflexes are a part of the temporary motor repertoire in early ontogeny, motor primitives refer to sets of motor patterns that are considered basic units of voluntary motor control thought to be present throughout the life-span. The article provides an overview of the anatomy and neurophysiology of human reflexive motor patterns to elucidate that both concepts are rooted in architecture of the spinal cord. I will advocate that an understanding of the human motor system that encompasses both primitive reflexes and motor primitives as well as the interaction with supraspinal motor centers will lead to an appreciation of the richness of the human motor repertoire, which in turn seems imperative for designing epigenetic robots and highly adaptable human machine interfaces.
Research Interests:
Kinaesthesia is the conscious perception of limb and body position, orientation, and motion. Recent studies have shown that patients with Parkinson’s disease have higher thresholds for detecting passive elbow movements, reflecting... more
Kinaesthesia is the conscious perception of limb and body position, orientation, and motion. Recent studies have shown that patients with Parkinson’s disease have higher thresholds for detecting passive elbow movements, reflecting kinaesthesic deficits.1 2 Patients with Parkinson’s disease show altered proprioception related EEG potentials during passive movements, which probably reflect changes in the cortical processing of kinaesthesic signals.3 Dopaminergic drugs appear to enhance this deficit.4 In contrast, we found no effect of levodopa on kinaesthesia.2 Deep brain stimulation of the subthalamic nucleus (STN-DBS) improves motor deficits in Parkinson’s disease5 but it may worsen cognitive functions such as working memory.6 However, the effects of STN-DBS on kinaesthesia are unknown. We therefore sought to determine how STN-DBS affects the perception of limb position.
Research Interests:
When humans are exposed to external forces while performing arm movements, they adapt by compensating for these novel forces. The basis of this learning process is thought to be a neural representation that models the relation between all... more
When humans are exposed to external forces while performing arm movements, they adapt by compensating for these novel forces. The basis of this learning process is thought to be a neural representation that models the relation between all forces acting upon the system and the kinematic effects they produce, called inverse dynamic model (IDM). The present study investigated whether and how the predictability of a given external force affects the selection of an appropriate motor response to compensate for such force. Adult human subjects (N=32) held a handle that could rotate around the elbow joint and learned to perform goal-directed forearm flexion movements, while an external velocity-dependent negative damping force was applied that assisted forearm movement. Subjects were randomly assigned to two groups. In the associative group, the applied damping force was always associated with a specific initial position. Thus, after initial learning , the force application became predictable. In the non-associative group, where the same movements were performed, the applied force was independent of the initial position, so that no association between force and location could be formed. We found that only the associative group significantly reduced target error when damping was present. That is, the location cue aided these subjects in generating dynamic responses in the appropriate limb. Our results indicate that motor adaptation to different dynamic environments can be facilitated by indicative stimuli.
Research Interests:
We investigated how humans with hereditary cerebellar degeneration [spinocerebellar ataxia (SCA) type 6 and 8, n 9] and age-and sex-matched healthy controls (n 9) adapted goal-directed arm movements to an unknown external force field. We... more
We investigated how humans with hereditary cerebellar degeneration [spinocerebellar ataxia (SCA) type 6 and 8, n 9] and age-and sex-matched healthy controls (n 9) adapted goal-directed arm movements to an unknown external force field. We tested whether learning could be generalized to untrained regions in the workspace, an aspect central to the idea of an internal model, and if any learning could be retained. After removal of the force field, SCA patients showed little or no learning-related aftereffects indicating that repeated force-field exposure never led to successful force compensation. In contrast, healthy control subjects quickly adapted their movements to the new force field. The difference in force adaptation was significant for movements to targets that required both the shoulder and elbow joint (P 0.001). Moreover, the generalization of learned movements to targets outside the learned workspace was prevented by the cerebellar degeneration (P 0.01). Retention of force adaptation was significantly lower in SCA patients (P 0.003). The severity of ataxia in SCA patients correlated negatively with the extent of learning (r 0.84, P 0.004). Our findings imply that progressive loss of cerebellar function gradually impairs force adaptation. The failure to generalize learning suggests that cerebellar degeneration prevents the formation of an internal representation of the limb dynamics.
Research Interests:
What is the relationship between development of the nervous system and the emergence of voluntary motor behavior? This is the central question of the nature-nurture discussion that has intrigued child psychologists and pediatric... more
What is the relationship between development of the nervous system and the emergence of voluntary motor behavior? This is the central question of the nature-nurture discussion that has intrigued child psychologists and pediatric neurologist for decades. This paper attempts to revisit this issue. Recent empirical evidence on how infants acquire multi-joint coordination and how children learn to adapt to novel force environments will be discussed with reference to the underlying development of the nervous system. The claim will be made that the developing human nervous system by no means constitutes an ideal controller. However, its redundancy, its ability to integrate multi-modal sensory information and motor commands and its facility of time-critical neural plasticity are features that may prove to be useful for the design of adaptive robots.
Research Interests:
The authors investigated adaptation of goal-directed forearm movements to unknown external viscous force assisting forearm flexion in 6 patients with cerebellar dysfunction and in 6 control participants. Motor performance was generally... more
The authors investigated adaptation of goal-directed forearm movements to unknown external viscous force assisting forearm flexion in 6 patients with cerebellar dysfunction and in 6 control participants. Motor performance was generally degraded in cerebellar patients and was markedly reduced under the force condition in both groups. however, patients and controls were able to adapt to the novel force within 8 trials. Only the healthy controls were able to improve motor performance when readapting to a null-force condition. The results indicate that cerebellar patients' motor control system has imprecise estimations of actual limb dynamics at its disposal. Force adaptation may have been preserved because single-joint movements were performed, where as the negative viscous force alone and no interaction forces had to be compensated.
Research Interests:
This study investigated force adaption in humans during goal-directed flexion forearm motion.
Research Interests:
Humans learn to make reaching movements 1n novel dynamic environments by acquiring an internal motor model of their limb dynamics. Here, the authors investigated how 4-to ll-year-old children (N = 39) and adults (N = 7) adapted to changes... more
Humans learn to make reaching movements 1n novel dynamic environments by acquiring an internal motor model of their limb dynamics. Here, the authors investigated how 4-to ll-year-old children (N = 39) and adults (N = 7) adapted to changes in arm dynamics, and they examined whether those data ruppö.t the view that the human brain acquires inverse dynamics möd"ls (IDM) during development. While external damping forces were applied, the children leamed to perform goal-directed forearm flexion movements. After changes in damping' all children showed kinematic aftereffects indicative of a neural controller that still attempted to compensate the no longer existing damping force. With increasing age, the number of trials toward co-plei" adaptation decreased. When damping was present' forearm paths were most perturbed and most variable in the youngest children but were improved in the older children. The findings indicate that the neural representations of limb dynamics are less precise in children and less stable in time than those of adults' Such controller instability might be a primary cause of the high kinematic variability observed in many motor tasks during childhood. Finally, the young children were not able to update those models at the same rate as the older children, who, in turn, adapted more slowly than adults. In conclusion, the ability to adapt to unknown forces is a developmental achievement. The present results are consistent with the view that the acquisition and modification of internal models of the limb dynamics form the basis of that adaptive process. A Outt humans learn to manipulate novel objects with Flrelative ease. As the result of practice, those objects are moved along desired, preplanned trajectories. The tra-jectories remain surprisingly stereotypic for a wide range of movement speeds and amplitudes despite the complexity of the underlying limb dynamics (Atkeson, 1989). The results of recent research on goal-directed action in adult humans suggest that neural representations of the limb dynamics or kinematics, so-called internal motor models, form the basis of that control process. In general, two types of internal
Research Interests:
Research Interests:
Precise knowledge about limb position and orientation is essential for the ability of the nervous system to plan and control voluntary movement. While it is well established that proprioceptive signals from peripheral receptors are... more
Precise knowledge about limb position and orientation is essential for the ability of the nervous system to plan and control voluntary movement. While it is well established that proprioceptive signals from peripheral receptors are necessary for sensing limb position and motion, it is less clear which supraspinal structures mediate the signals that ultimately lead to the conscious awareness of limb position (kinaesthesia). Recent functional imaging studies have revealed that the cerebellum, but not the basal ganglia, are involved in sensory processing of proprioceptive information induced by passive and active movements. Yet psychophysical studies have suggested a prominent role of the basal ganglia in kinaesthesia. This study addresses this apparent dichotomy by investigating the contributions of the cerebellum and the basal ganglia to the perception of limb position. Using a passive movement task, we examined the elbow position sense in patients with a dysfunction of the basal ganglia (Parkinson's disease, n = 9), patients with cerebellar degeneration [spinocerebellar ataxia (SCA) types 6 and 8, n = 6] and age-matched healthy control subjects (n = 11). In comparison with healthy control subjects, Parkinson's disease patients, but not SCA patients, were significantly impaired in the ability to detect displacements correctly. A 1° forearm displacement was correctly recognized in >75% of trials by control subjects and SCA patients, but only in 55% of Parkinson's disease patients. Only at 6° displacement did Parkinson's disease patients exhibit a response rate similar to those of the two other groups. Thresholds for 75% correct responses were 1.03° for controls, 1.15° for cerebellar patients and 2.10° for Parkinson's disease patients. This kinaesthetic impairment significantly correlated with the severity of disease in Parkinson's disease patients, as determined by the Unified Parkinson's Disease Rating Scale (r = ±0.7, P = 0.03) and duration of disease (r = ±0.7, P = 0.05). In contrast, there was no significant correlation between performance and the daily levodopa equivalent dose. These results imply that an intact cerebro-basal ganglia loop is essential for awareness of limb position and suggest a selective role of the basal ganglia but not the cerebellum in kinaesthesia.
Research Interests:
Hereditary cerebellar ataxia progressively impairs force adaptation during goal-directed arm movements. J Neurophysiol 91: 230–238, 2004. First published September 17, 2003; 10.1152/jn.00557.2003. We investigated how humans with... more
Hereditary cerebellar ataxia progressively impairs force adaptation during goal-directed arm movements. J Neurophysiol 91: 230–238, 2004. First published September 17, 2003; 10.1152/jn.00557.2003. We investigated how humans with hereditary cerebellar degeneration [spinocerebellar ataxia (SCA) type 6 and 8, n 9] and age- and sex-matched healthy controls (n 9) adapted goal-directed arm movements to an unknown external force field. We tested whether learning could be generalized to untrained regions in the workspace, an aspect central to the idea of an internal model, and if any learning could be retained. After removal of the force field, SCA patients showed little or no learning-related aftereffects indicating that repeated force-field exposure never led to successful force compensation. In contrast, healthy control subjects quickly adapted their movements to the new force field. The difference in force adaptation was significant for movements to targets that required both the shoulder and elbow joint (P 0.001). Moreover, the generalization of learned movements to targets outside the learned workspace was prevented by the cerebellar degeneration (P 0.01). Retention of force adaptation was significantly lower in SCA patients (P 0.003). The severity of ataxia in SCA patients correlated negatively with the extent of learning (r 0.84, P 0.004). Our findings imply that progressive loss of cerebellar function gradually impairs force adaptation. The failure to generalize learning suggests that cerebellar degeneration prevents the formation of an internal representation of the limb dynamics.
Research Interests:
When humans are exposed to external forceswhile performing arm movements, they adapt by compensating for these novel forces. The basis of this learning process is thought to be a neural representation that models the relation between all... more
When humans are exposed to external forceswhile performing arm movements, they adapt by compensating for these novel forces. The basis of this learning process is thought to be a neural representation that models the relation between all forces acting upon the system and the kinematic effects they produce, called inverse dynamic model (IDM). The present study investigated whether and how the predictability of a given external force affects the selection of an appropriate motor response to compensate for such force.Adult human subjects (N =32) held a handle that could rotate around the elbow joint and learned to perform goal-directed forearm flexion movements, while an external velocity-dependent negative damping force was applied that assisted forearm movement. Subjects were randomly assigned to two groups. In the associative group, the applied damping force was always associated with a specific initial position. Thus, after initial learn-ing, the force application became predictable. In the non-associative group, where the same movements were performed, the applied force was independent of the initial position, so that no association between force and location could be formed. We found that only the associative group significantly reduced target error when damping was present. That is, the location cue aidedthese subjects in generating dynamic responses in theappropriate limb. Our results indicate that motor adaptation to different dynamic environments can be facilitated by indicative stimuli.
Research Interests:
Neurobiological evidence reveals that neurally coded inverse models of limb dynamics form the basis for feed-forward motor control in humans. This study investigates the role of visual feedback for the acquisition of inverse motor models... more
Neurobiological evidence reveals that neurally coded inverse models of limb dynamics form the basis for feed-forward motor control in humans. This study investigates the role of visual feedback for the acquisition of inverse motor models in children and adults. Eight 9-year-old and eight 5-year-old children and eight adults performed goal-directed horizontal forearm movements using a single-joint arm manipulandum. When visual feedback was not available before and after movement execution did not affect adult motor performance. In contrast, spatial error increased in both children groups when visual feedback was removed. Spatial accuracy was improved during the partial feedback condition, if children had prior practice under full visual feedback. The increased dependence on visual feedback, especially in the younger children, is a sign that children relied predominantly on central feedback mechanisms for motor control, because their feed-forward control was not yet functional. The reasons for the lack of feed-forward control are twofold: first, there are problems in motor planning, specifically with the inverse kinematic transformation (from hand position to joint angles). Second, there are deficits in the neural controller, specifically due to imprecise neural estimations of the true limb dynamics.
Research Interests:
When humans perform goal-directed arm movements under the influence of an external damping force, they learn to adapt to these external dynamics. After removal of the external force field, they reveal kinematic aftereffects that are... more
When humans perform goal-directed arm movements under the influence of an external damping force, they learn to adapt to these external dynamics. After removal of the external force field, they reveal kinematic aftereffects that are indicative of a neural controller that still compensates the no longer existing force. Such behavior suggests that the adult human nervous system uses a neural representation of inverse arm dynamics to control upper-extremity motion. Central to the notion of an inverse dynamic model (IDM) is that learning generalizes. Consequently, aftereffects should be observable even in untrained workspace regions. Adults have shown such behavior, but the ontogenetic development of this process remains unclear. This study examines the adap-tive behavior of children and investigates whether learning a force field in one hemifield of the right arm work-space has an effect on force adaptation in the other hemi-field. Thirty children (aged 6–10 years) and ten adults performed 30° elbow flexion movements under two conditions of external damping (negative and null). We found that learning to compensate an external damping force transferred to the opposite hemifield, which indicates that a model of the limb dynamics rather than an association of visited space and experienced force was acquired. Aftereffects were more pronounced in the younger children and readaptation to a null-force condition was prolonged. This finding is consistent with the view that IDMs in children are imprecise neural representations of the actual arm dynamics. It indicates that the acquisition of IDMs is a developmental achievement and that the human motor system is inherently flexible enough to adapt to any novel force within the limits of the organism's biomechanics.
Research Interests:
Neurobiological evidence reveals that neurally coded inverse models of limb dynamics form the basis for feed-forward motor control in humans. This study investigates the role of visual feedback for the acquisition of inverse motor models... more
Neurobiological evidence reveals that neurally coded inverse models of limb dynamics form the basis for feed-forward motor control in humans. This study investigates the role of visual feedback for the acquisition of inverse motor models in children and adults. Eight 9-year-old and 5-year-old children and eight adults performed goal-directed horizontal forearm movements using a single-joint arm manipulandum. When visual feedback was not available before and after movement execution (partial feedback), spatial error increased in adults and children. however, the lack of visual information during the movement execution did not affect adult motor performance. In contrast, spatial error increased in both children groups when visual feedback was removed. Spatial accuracy was improved during the partial feedback condition, if children had prior practice under full visual feedback. The increased dependence on visual feedback, especially in the younger children, is a sign that children relied predominantly on central feedback mechanisms for motor control, because their feed--forward control was not yet functional. The reasons for the lack of feed-forward control are twofold: First, there are problems in motor planning, specifically with the inverse kinematics transformation (from hand position to join angles). Second, there are deficits in the neural controller, specifically due to imprecise neural estimations of the true limb dynamics.
Research Interests:
Within the context of the Ebbinghaus illusion, adults regularly misjudge the physical size of a centre disc, yet scale their hand aperture according to its actual size. Separate visual pathways for perception and action are assumed to... more
Within the context of the Ebbinghaus illusion, adults regularly misjudge the physical size of a centre disc, yet scale their hand aperture according to its actual size. Separate visual pathways for perception and action are assumed to account for this finding. The dorsal visual stream is said to elaborate on egocentric (visuomotor), while the ventral stream is involved in allocentric transformations (object recognition). This study examines the ontogenetic development of this dissociation between perception and action in 35 children between the ages of 5 and 12 years. We report four major results. First, when children judged object size without grasping the disc, their judgements were deceived by the illusion to the same extent as adults. However, when asked to estimate size and then to grasp the disc, young children's (5–7 years) perceptual judgements became unreliable, while adults were still reliably deceived by the illusion in 80% of their trials. Second, the younger the children, the more their aperture was affected by the illusional surround. Discs of the same size were grasped with a smaller aperture when surrounded by a small annulus, although they were perceived as being larger. Third, young children used the largest safety margin during grasping. Fourth, the reliance on visual feedback decreased with increasing age, which was documented by shorter movement times and earlier maximum hand opening during grasping in the older children (feedforward control). Our results indicate that grasping behaviour in children is subject to an interaction between ventral and dorsal processes. Both pathways seem not to be functionally segregated in early and middle childhood. The data are inconclusive about whether young children predominantly use a specific visual stream for either a perceptual or motor task. However, our data demonstrate that children were relying on both visual processing streams during perceptual as well as visuomotor tasks. We found that children used egocentric cues to make perceptual judgements, while their grasping gestures were not exclusively shaped by viewer-centred but also by object-centred information .
Research Interests:
Research Interests:
This study examined the movement process-product relationship from a developmental perspective. The authors used multiple regression to investigate the changing relationship between qualitative movement descriptions of the overarm throw... more
This study examined the movement process-product relationship from a developmental perspective. The authors used multiple regression to investigate the changing relationship between qualitative movement descriptions of the overarm throw and the throwing outcome, horizontal ball velocity. Seventeen girls and 22 bays were filmed longitudinally at ages 6, 7, 8, and 13 years. Their movements were assessed using Robertons (Roberton & Halverson, 1984) developmental sequences for action of the humerus, forearm, trunk, stepping, and stride length. The sequences accounted for 69-85 % (adjusted) of the total velocity variance each year. The components that best predicted ball velocity changed overtime, although humerus or forearm action always accounted for considerable variance. Gender was a good predictor of ball velocity, but if the developmental descriptions were entered first in a stepwise regression, gender then explained no more than 2 % additional variance.
Research Interests:
Short term vibration of the dorsal neck muscles (10–35 s) is known to induce involuntary movements of the head in patients with spasmodic torticollis. To investigate whether neck muscle vibration might serve as a therapeutic tool when... more
Short term vibration of the dorsal neck muscles (10–35 s) is known to induce involuntary movements of the head in patients with spasmodic torticollis. To investigate whether neck muscle vibration might serve as a therapeutic tool when applyed for a longer time interval, we compared a vibration interval of 5 seconds with a 15 minute interval in a patient with spasmodic torticollis with an extreme head tilt to the right shoulder. Head position was recorded with a two camera optoelectronic motion analyzer in six diVerent test conditions. Vibration regularly induced a rapid change of head position that was markedly closer to a normal, upright posture. After 5 seconds of vibration, head position very quickly returned to the initial position within seconds. During the 15 minute interval, head position remained elevated. After terminating vibration in this condition, the corrected head position remained stable at first and then decreased slowly within minutes to the initial tilted position. Conclusions—(1) In this patient, muscle vibration was the specific sensory input that induced lengthening of the dystonic neck muscles. Neither haptic stimulation nor transcutaneous electrical stimulation had more than a marginal eVect. (2) The marked diVerence in the change of head position after short and prolonged stimulation supports the hypothesis that spasmodic torticollis might result from a disturbance of the central processing of the aVerent input conveying head position information—at least in those patients who are sensitive to sensory stimulation in the neck region. (3) Long term neck muscle vibration may provide a convenient non-invasive method for treating spasmodic torticollis at the central level by influencing the neural control of head on trunk position.
Research Interests:
Objectives—To examine changes in predictive control of early antagonist responses to limb perturbations in patients with defined lesions of the cerebellum. Methods—Eight cerebellar patients and eight sex and age matched control subjects... more
Objectives—To examine changes in predictive control of early antagonist responses to limb perturbations in patients with defined lesions of the cerebellum. Methods—Eight cerebellar patients and eight sex and age matched control subjects participated. Subjects held a handle that was rotated around the elbow joint. They were instructed to hold the forearm at 90° flexion against a mechanical perturbation. Extensor torque (5 Nm) was applied for 140 ms (pulse), or for 1400 ms (step) through an external motor. Motor responses were tested under two divergent conditions of anticipatory information. In the expected condition, subjects anticipated and received a pulse. Under the unexpected condition, subjects expected steps, but received unexpected pulses. Biceps and triceps EMG as well as angular kinematics were compared between expected and unexpected pulse perturbations to quantify possible effects of prediction. Results—In all healthy subjects, the degree of overshoot in the return flexion movement was significantly less in expected pulse perturbations compared with unexpected trials. The degree of amplitude reduction was significantly smaller in the patient group than in the control group (22.8% v 40.0%). During the expected trials, latency of peak triceps activity was on average 20% shorter in the control group, but 4% larger in the cerebellar patients. Conclusions—In the expected condition, controls achieved a significant reduction in angular amplitude by generating triceps activity earlier, whereas the ability to use prediction for adjusting early antagonist responses after limb perturbation was impaired in cerebellar patients.
Research Interests:
It has been suggested that the movement impairments experienced by patients with neglect are not restricted to spatial disorders, but also affect higher order kinematics (velocity and acceleration) to the extent that movements towards the... more
It has been suggested that the movement impairments experienced by patients with neglect are not restricted to spatial disorders, but also affect higher order kinematics (velocity and acceleration) to the extent that movements towards the neglected side are slower than movements away from it. In a recent study, we could not confirm this hypothesis, but found that patients with unilateral neglect exhibited no distinct direction-specific deficits in hand velocity when performing goal-directed reaching movements. Here we investigated whether neglect patients might reveal direction-specific deficits during exploratory hand movements. Six patients with left-sided neglect and six age-matched healthy control subjects scanned with their right hands the surface of a large table searching for a (non-existent) tactile target. Movements were performed in darkness. Time-position data of the hand were recorded with an optoelectronic camera system. Median activity of the patients’ exploratory hand movements was shifted to the right (Karnath and Perenin 1998). Hand trajectories were partitioned into sections of leftward/rightward or, along the sagittal plane, into sections of near/far movements. For each movement section average and peak velocities were computed. The patients’ hand movements were bradykinetic when compared with the control group. However, we found no evidence that average or peak velocities of leftward intervals were systematically lower than during rightward motion. Direction-specific deficits in velocity were also not observed for movements to and away from the body (sagittal plane). In conclusion, we found evidence for general bradykinesia in neglect patients but not for a direction-specific deficit in the control of hand velocity during exploratory hand movements.
Research Interests:
Knowledge of how stiffness, damping and the equilibrium position of specific limbs change during voluntary motion is important for understanding basic strategies of neuromotor control. Presented here is an algorithm for identifying... more
Knowledge of how stiffness, damping and the equilibrium position of specific limbs change during voluntary motion is important for understanding basic strategies of neuromotor control. Presented here is an algorithm for identifying time-dependent changes in joint stiffness, damping, and equilibrium position of the human forearm. The procedure requires data from only a single trial. The method relies neither on an analysis of the resonant frequency of the arm nor on the presence of an external bias force. Its validity was tested with a stimulated forward model of the human forearm. Using the parameter estimations as forward model input, the angular kinematics (model output) were reconstructed and compared to the empirically measure data. Identification of mechanical impedance is based on a least-squares solution of the model equation. As a regularization technique and to improve the temporal resolution of the identification process, a moving temporal window with a variable width was imposed. The method's performance was tested by (a) identifying a priori known hypothetical time-series of stiffness, damping and equilibrium position, and (b) determining impedance parameters from recorded single joint forearm movements during a hold and a goal-directed movement task. The method reliably reconstructed the original angular kinematics of the artificial and human data with an average positional error of less than .05 rad for movement amplitudes of up to 0.9 rad, and did not yield hypermetric trajectories like previous procedures not accounting for damping.
Research Interests:
The aim of the present paper is to propose that the adoption of a framework of biological development is suitable for the construction of artificial systems. We will argue that a developmental approach does provide unique insights on how... more
The aim of the present paper is to propose that the adoption of a framework of biological development is suitable for the construction of artificial systems. We will argue that a developmental approach does provide unique insights on how to build highly complex and adaptable artificial systems. To illustrate our point, we will use as an example the acquisition of goal-directed reaching. In the initial part of the paper we will outline (a) how mechanisms of biological development can be adapted to the artificial world, and (b) how this artificial development differs from traditional engineering approaches to robotics. An experiment performed on an artificial system initially controlled by motor reflexes is presented, showing the acquisition of visuomotor maps for ballistic control of reaching without explicit knowledge of the system’s kinematic parameters.
Research Interests:
Neuromagnetic responses to separate tactile stimulation of digits I, II and V and simultaneous stimulation of digit pairs II and I, and II and V, were recorded in six healhty adult subjects using a 122-channel whole-head neuromagnetometer... more
Neuromagnetic responses to separate tactile stimulation of digits I, II and V and simultaneous stimulation of digit pairs II and I, and II and V, were recorded in six healhty adult subjects using a 122-channel whole-head neuromagnetometer in order to investigate functional overlap of finger representations in primary somatosensory cortex (SI). Evoked responses to single digit stimulation were explained by time-varying equivalent current dipoles (ECDs) located in SI. These ECDs were then used to explain responses to stimulation of digit pairs. A cortical interaction ratio (IR( was defined as the vector sum of peak source amplitudes to separate stimulation of two fingers divided by the vector sum of source amplitudes to simultaneous stimulation of the two digits. Mean IR was significantly higher (P<0.05; Wilcoxon test) for digital pair II + I (1.69 +/- 0.15) compared to digit pair II + V ((1.14 +/- 0.12). These results indicate that there is an overlap of finger representations in human SI which differs between anatomically adjacent and non-adjacent digit pairs.
Research Interests:
Do patients with unilateral neglect exhibit direction-specific deficits in the control of movement velocity when performing goal-directed arm movements? Five patients with left-sided neglect performed unrestrained three-dimensional... more
Do patients with unilateral neglect exhibit direction-specific deficits in the control of movement velocity when performing goal-directed arm movements? Five patients with left-sided neglect performed unrestrained three-dimensional pointing movements to visual targets presented at body midline, the left and right hemispace. A group of healthy adults and a group of patients with right-hemispheric brain damage but no neglect served as controls. Pointing was performed under normal room light or in darkness. Time-position data of the hand were recorded with an opto-electronic camera system. We found that compared to healthy controls, movement times were longer in both patient groups due to prolonged acceleration and deceleration phases. Tangential peak hand velocity was lower in both patient groups, but not significantly different from controls. Single peak, bell-shaped velocity profiles of the hand were preserved in all right hemispheric patients and in three out of five neglect patients. Most important, the velocity profiles of neglect patients to leftward targets did not differ significantly from those to targets in the right hemispace. In summary, we found evidence for general bradykinesia in neglect patients, but not for a direction-specific deficit in the control of hand velocity. We conclude that visual neglect induces characteristic changes in exploratory behavior, but not in the kinematics of goal-directed movements to objects in peripersonal space.
Research Interests:
Kinematic abnormalities of fast multijoint movements in cerebellar ataxia include abnormally increased curvature of hand trajectories and an increased hand path and are thought to originate from an impairment in generating appropriate... more
Kinematic abnormalities of fast multijoint movements in cerebellar ataxia include abnormally increased curvature of hand trajectories and an increased hand path and are thought to originate from an impairment in generating appropriate levels of muscle torques to support normal coordination between shoulder and elbow joints. Such a mechanism predicts that kinematic abnormalities are pronounced when fast movements are performed and large muscular torques are required. Experimental evidence that systematically explores the effects of increasing movement velocities on movement kinematics in cerebellar multijoint movements is limited and to some extent contradictory. We, therefore, investigated angular and hand kinematics of natural multijoint pointing movements in patients with cerebellar degenerative disorders and healthy controls. Subjects performed self-paced vertical pointing movements with their right arms at three different target velocities. Limb movements were recorded in three-dimensional space using a two-camera infra-
red tracking system. Differences between patients and healthy subjects were most prominent when the subjects performed fast movements. Peak hand acceleration and deceleration were similar to normals during slow and moderate velocity movements but were smaller for fast
movements. While altering movement velocities had little or no effect on the length of the hand path and angular motion of elbow and shoulder joints in normal subjects, the patients exhibited overshooting motions (hypermetria) of the hand and at both joints as movement velocity increased. Hypermetria at one joint always accompanied hypermetria at the neighboring joint. Peak elbow angular deceleration was markedly delayed in patients compared with normals. Other temporal movement variables such as the relative timing of shoulder and elbow joint motion onsets were normal in patients. Kinematic abnormalities of multijoint arm movements in cerebellar ataxia include hypermetria at both the elbow and the shoulder joint and, as a consequence, irregular and enlarged paths of the hand, and they are marked with fast but not with slow movements. Our findings suggest that kinematic movement abnormalities that characterize cerebellar limb ataxia are related to an impairment in scaling movement variables such as joint acceleration and deceleration normally with movement speed. Most likely, increased hand paths and decomposition of movement during slow movements, as described earlier, result from compensatory mechanisms the patients may employ if maximum movement accuracy is required.
red tracking system. Differences between patients and healthy subjects were most prominent when the subjects performed fast movements. Peak hand acceleration and deceleration were similar to normals during slow and moderate velocity movements but were smaller for fast
movements. While altering movement velocities had little or no effect on the length of the hand path and angular motion of elbow and shoulder joints in normal subjects, the patients exhibited overshooting motions (hypermetria) of the hand and at both joints as movement velocity increased. Hypermetria at one joint always accompanied hypermetria at the neighboring joint. Peak elbow angular deceleration was markedly delayed in patients compared with normals. Other temporal movement variables such as the relative timing of shoulder and elbow joint motion onsets were normal in patients. Kinematic abnormalities of multijoint arm movements in cerebellar ataxia include hypermetria at both the elbow and the shoulder joint and, as a consequence, irregular and enlarged paths of the hand, and they are marked with fast but not with slow movements. Our findings suggest that kinematic movement abnormalities that characterize cerebellar limb ataxia are related to an impairment in scaling movement variables such as joint acceleration and deceleration normally with movement speed. Most likely, increased hand paths and decomposition of movement during slow movements, as described earlier, result from compensatory mechanisms the patients may employ if maximum movement accuracy is required.
Research Interests:
In cerebellar ataxia, kinematic aberrations of multijoint movements are thought to originate from deficiencies in generating muscular torques that are adequate to control the mechanical consequences of dynamic inter- action forces. At... more
In cerebellar ataxia, kinematic aberrations of multijoint movements are thought to originate from deficiencies in generating muscular torques that are adequate to control the mechanical consequences of dynamic inter- action forces. At this point the exact mechanisms that lead to an abnormal control of interaction torques are not known. In principle, the generation of inadequate muscular torques may result from an impairment in generating sufficient levels of torques or from an inaccurate assessment and prediction of the mechanical consequences of movements of one limb segment on adjacent joints. We sought to differentiate the relative contribution of these two mechanisms and, therefore, analyzed intersegmental dynamics of multijoint pointing movements in healthy subjects and in patients with cerebellar degeneration. Un- restrained vertical arm movements were performed at three different target movement velocities and recorded using an optoelectronic tracking system. An inverse dynamics approach was employed to compute net joint torques, muscular torques, dynamic interaction torques and gravitational torques acting at the elbow and shoulder joint. In both groups, peak dynamic interaction forces and peak muscular forces were largest during fast movements. In contrast to normal subjects, patients produced hypermetric movements when executing fast movements. Hypermetric movements were associated with smaller peak muscular torques and smaller rates of torque change at elbow and shoulder joints. The patients deficit in generating appropriate levels of muscular force were prominent during two different phases of the pointing movement. Peak muscular forces at the elbow were reduced during the initial phase of the movement when simultaneous shoulder joint flexion generated an extensor influence upon the elbow joint. When attempting to terminate the movement, gravitational and dynamic interaction forces caused overshooting extension at the elbow joint. In normal subjects, muscular torque patterns at shoulder and elbow joint were synchronized in that peak flexor and extensor muscular torques occurred simultaneously at both joints. This temporal pattern of muscular torque generation at shoulder and elbow joint was preserved in patients. Our data suggest that an impairment in generating sufficient levels of phasic muscular torques significantly contributes to the patients difficulties in controlling the mechanical consequences of dynamic interaction forces during multijoint movements.
Research Interests:
It has been suggested that the movement impairments experienced by patients with neglect are not restricted to spatial disorders, but also affect higher-order kinematics (velocity and acceleration) to the extent that movements towards the... more
It has been suggested that the movement impairments
experienced by patients with neglect are not
restricted to spatial disorders, but also affect higher-order
kinematics (velocity and acceleration) to the extent that
movements towards the neglected side are slower than
movements away from it. In a recent study, we could not
confirm this hypothesis, but found that patients with unilateral
neglect exhibited no distinct direction-specific
deficits in hand velocity when performing goal-directed
reaching movements. Here we investigated whether neglect
patients might reveal direction-specific deficits
during exploratory hand movements. Six patients with
left-sided neglect and six age-matched healthy control
subjects scanned with their right hands the surface of a
large table searching for a (non-existent) tactile target.
Movements were performed in darkness. Time-position
data of the hand were recorded with an optoelectronic
camera system. Median activity of the patients’ exploratory
hand movements was shifted to the right (Karnath
and Perenin 1998). Hand trajectories were partitioned into
sections of leftward/rightward or, along the sagittal
plane, into sections of near/far movements. For each
movement section average and peak velocities were
computed. The patients’ hand movements were bradykinetic
when compared with the control group. However,
we found no evidence that average or peak velocities of
leftward intervals were systematically lower than during
rightward motion. Direction-specific deficits in velocity
were also not observed for movements to and away from
the body (sagittal plane). In conclusion, we found evidence
for general bradykinesia in neglect patients but not
for a direction-specific deficit in the control of hand velocity
during exploratory hand movements.
experienced by patients with neglect are not
restricted to spatial disorders, but also affect higher-order
kinematics (velocity and acceleration) to the extent that
movements towards the neglected side are slower than
movements away from it. In a recent study, we could not
confirm this hypothesis, but found that patients with unilateral
neglect exhibited no distinct direction-specific
deficits in hand velocity when performing goal-directed
reaching movements. Here we investigated whether neglect
patients might reveal direction-specific deficits
during exploratory hand movements. Six patients with
left-sided neglect and six age-matched healthy control
subjects scanned with their right hands the surface of a
large table searching for a (non-existent) tactile target.
Movements were performed in darkness. Time-position
data of the hand were recorded with an optoelectronic
camera system. Median activity of the patients’ exploratory
hand movements was shifted to the right (Karnath
and Perenin 1998). Hand trajectories were partitioned into
sections of leftward/rightward or, along the sagittal
plane, into sections of near/far movements. For each
movement section average and peak velocities were
computed. The patients’ hand movements were bradykinetic
when compared with the control group. However,
we found no evidence that average or peak velocities of
leftward intervals were systematically lower than during
rightward motion. Direction-specific deficits in velocity
were also not observed for movements to and away from
the body (sagittal plane). In conclusion, we found evidence
for general bradykinesia in neglect patients but not
for a direction-specific deficit in the control of hand velocity
during exploratory hand movements.
Research Interests:
Research Interests:
This study addresses the question of whether external timing signals and/or simultaneous rhythmic movements of other limbs can alleviate sequencing motor deficits associated with Parkinson's disease (PD). Subjects performed rhythmic lip... more
This study addresses the question of whether external timing signals and/or simultaneous rhythmic movements of other limbs can alleviate sequencing motor deficits associated with Parkinson's disease (PD). Subjects performed rhythmic lip and finger movements simultaneously or in isolation. In addition, they had to self-pace their movements or match them to an external signal. Our results are summarized as follows: (a) Seven of 12 patients had adequate mean repetition rates; that is, they fulfilled the task requirements on a global scale. The remaining five patients had various degrees of hastened responses and were not fully able to synchronize their movements to an external pacing signal. (b) PD patients exhibited hypometria in their finger tapping, but not in their lip movements. Their movements were not abnormally slowed, but peak velocity was appropriately scaled, even to reduced movement amplitudes. (c) Mean repetition rates, stability of frequency response, and kinematics did not differ between conditions of external and internal stimulation within the PD group, but were different from the control group performance. (d) Kinematic measures were not improved during dual-task execution. PD patients were not able to maintain a 1: 1 rhythm between effec-tors. The incidence of hastening increased during simultaneous motor execution. We conclude that the use of external pacing signals might aid movement initiation of PD patients, but does not improve their temporal or spatial coordination when generating repetitive movements. Simultaneous execution does not necessarily enhance motor performance, but might actually have detrimental effects in patients prone to hastening.
Research Interests:
We recorded reaching movements from nine infants longitudinally from the onset of reaching (5th postnatal month) up to the age of 3 years. Here we analyze hand and proximal joint trajectories and examine the emerging temporal coordination... more
We recorded reaching movements from nine infants longitudinally from the onset of reaching (5th postnatal month) up to the age of 3 years. Here we analyze hand and proximal joint trajectories and examine the emerging temporal coordination between arm segments. The present investigation seeks (a) to determine when infants acquire consistent, adult-like patterns of multijoint coordination within that 3-year period, and (b) to relate their hand trajectory formation to underlying patterns of proximal joint motion (shoulder, elbow). Our results show: First, most kinematic parameters do not assume adult-like levels before the age of 2 years. At this time, 75% of the trials reveal a single peaked velocity profile of the hand. Between the 2nd and 3rd year of life, ªimprovementsº of hand-or joint-related movement units are only marginal. Second, infant motor systems strive to obtain velocity patterns with as few force reversals as possible (uni-or bimodal) at all three limb segments. Third, the formation of a consistent interjoint synergy between shoulder and elbow motion is not achieved within the 1st year of life. Stable patterns of temporal coordination across arm segments begin to emerge at 12±15 months of age and continue to develop up to the 3rd year. In summary , the development toward adult forms of multijoint coordination in goal-directed reaching requires more time than previously assumed. Although infants reliably grasp for objects within their workspace 3±4 months after the onset of reaching, stereotypic kinematic motor patterns are not expressed before the 2nd year of life.
Research Interests:
Research Interests:
The present study investigated unrestrained, three-dimensional arm movements during goal-directed pointing in five patients with clinically manifest neglect to targets positioned either in the center or the left and right hemispace. Five... more
The present study investigated unrestrained, three-dimensional arm movements during goal-directed pointing in five patients with clinically manifest neglect to targets positioned either in the center or the left and right hemispace. Five patients with unilateral right hemispheric lesions without neglect and six healthy subjects served as controls. All subjects were able to point to these targets. Terminal accuracy of pointing did not differ between the three groups along the horizontal, vertical and anterior posterior axis. Subjects' hand trajectories did not reveal direction-specefic deviations from a straight-line hand path. Our data show that deviations in the trajectories toward the ipsilesional side are not characteristic for patients with spatial neglect. We argue that exploratory and goal-directed behavior might not share the same egocentric, body-centered reference frame. A spatial reference by eye or limb movements. Its failure does not induce a spatial bias in hand trajectory formation during goal-directed arm movements in peripersonal space. Such deviations of reaching or pointing rather seem to be characteristic for patients with optic ataxia.
Research Interests:
Recent clinical data indicate that internal cueing mechanisms required for the triggering of movement sequences are impaired in Parkinson's disease (PD). Nevertheless , most PD subjects produce maximal syllable repetition rates similar to... more
Recent clinical data indicate that internal cueing mechanisms required for the triggering of movement sequences are impaired in Parkinson's disease (PD). Nevertheless , most PD subjects produce maximal syllable repetition rates similar to those observed in healthy control individuals during oral diadochokinesis tasks. There is some evidence that tremor oscillations may pace repetitive movements in Parkinso-nians giving rise to hastening phenomena. Conceivably, the performance of PD patients in syllable repetition tasks thus reflects a specific timing deficit, i.e., articula-tory hastening. It is the aim of the present study to investigate the contribution of speech hastening to oral diadochokinesis in the presence of internal and external cues. By means of an optoelectric movement analysis system, the displacements of the lips during repetitions of the syllable /pa/ were recorded in two akinetic-rigid PD individuals. Subjects were asked to synchronize labial diadochokinesis to sequences of periodic acoustic stimuli (2.5–6 Hz). One of the PD patients showed speech hastening, i.e., he produced repetitions of 8 to 9 Hz whenever stimulus frequencies exceeded 4 Hz. The other Parkinsonian adequately matched the stimulus frequencies required. However, she achieved a higher diadochokinesis rate in the matching task than under the instruction to repeat ''as fast as possible.'' Thus, the presence of an external cue improved performance. In conclusion, our data indicate two deficits of the temporal control of repetitive articulatory gestures in PD: speech hastening and impaired self-paced sequencing. These two pathomechanisms may allow to reconcile the controversial findings on oral diadochokinesis in PD reported so far.
Research Interests:
Nine young infants were followed longitudinally from 4 to 15 months of age. They performed multi joint reaching movements to a stationary target presented at shoulder height. Time-position data of the hand, shoulder, and elbow were... more
Nine young infants were followed longitudinally from 4 to 15 months of age. They performed multi joint reaching movements to a stationary target presented at shoulder height. Time-position data of the hand, shoulder, and elbow were collected using an optoelectronic measurement system. In addition, we recorded electromyographic activity (EMG) from arm extensors and flexors. This paper documents how control problems of proximal torque generation may account for the segmented hand paths seen during early reaching. Our analysis revealed the following results: first, muscular impulse (integral of torque) increased significantly between the ages of 20 (reaching onset) and 64 weeks. That is, as infants got older they produced higher levels of mean muscular flexor torque during reaching. Data were normalized by body weight and movement time, so differences are not explained by anthropometric changes or systematic variations in movement time. second, while adults produced solely flexor muscle torque to accomplish the task, infants generated flexor and extensor muscle torque at shoulder and elbow throughout a reach. At reaching onset more than half of the trials revealed this latter kinetic profile. Its frequency declined systematically as infants got older. Third, we examined the pattern of muscle coordination in those trials that exhibited elbow extensor muscle torque. We found that during elbow extension co-activation of flexor and extensor muscles was the predominant pattern in 67% of the trials. This pattern was notably absent in comparable adult reaching movements. Fourth, fluctuations in force generation, as measured by the rate of change of total torque (NET) and muscular torque (MUS), were more frequent in early reaching (20-28 weeks) than in the older cohort (52-64 weeks), indicating that muscular torque production became increasingly smoother and task-efficient. Our data demonstrate that young infants have problems in generating smooth profiles of proximal joint torques. One possible reason for this imprecision in infant force control is their inexperience in predicting the magnitude and direction of external forces. That infants learned to consider external forces is documented by their increasing reliance on these forces when performing voluntary elbow extensions. The patterns of muscle coordination underlying active elbow extensions were basically the same as during the prereaching phase, indicating that the formation of functional synergies is based on basal repertoire of innervation patterns already observable in very early, spontaneous movements.
Research Interests:
this study addresses the question of whether external timing signals and/or simultaneous rhythmic movements of other limbs can alleviate sequencing motor deficits associated with Parkinson's disease (PD). Subjects performed rhythmic lip... more
this study addresses the question of whether external timing signals and/or simultaneous rhythmic movements of other limbs can alleviate sequencing motor deficits associated with Parkinson's disease (PD). Subjects performed rhythmic lip and finger movements simultaneously or in isolation. In addition, they had to self-pace their movements or match them to an external signal. Our results are summarized as follows: (a) Seven of 12 patients had adequate mean repetition rates; that is, they fulfilled the task requirements on a global scale. the remaining five patients had various degrees of hastened responses and were not fully able to synchronize their movements to an external pacing signal. (b) PD patients exhibited hypometria in their finger tapping, but not in their lip movements. their movements were not abnormally slowed, but peak velocity was appropriately scaled, even reduced to movement amplitudes. (c) Mean repetition rates, stability of frequency response, and kinematics did not differ between conditions of external and internal stimulation within the Pd group, but were different from the control group performance. (d) Kinematic measures were not improved ruing dual-task execution. PD patients were not able to maintain a 1:1 rhythm between effectors. The incidence of hastening increased during simultaneous motor execution. We conclude that the use of external pacing signals might aid movement initiation of PD patients, but does not improve their temporal or spatial coordination when generating repetitive movements. Simultaneous execution does not necessarily enhance motor performance, but might actually have detrimental effects in patients prone to hastening.
Research Interests:
Recent clinical data indicate that internal cueing mechanisms required for the triggering of movement sequences are impaired in Parkinson’s disease (PD). Nevertheless, most PD subjects produce maximal syllable repetition rates similar to... more
Recent clinical data indicate that internal cueing mechanisms required for the triggering of movement sequences are impaired in Parkinson’s disease (PD). Nevertheless, most PD subjects produce maximal syllable repetition rates similar to those observed in healthy control individuals during oral diadochokinesis tasks. There is some evidence that tremor oscillations may pace repetitive movements in Parkinsonians giving rise to hastening phenomena. Conceivably, the performance of PD patients in syllable repetition tasks thus reflects a specific timing deficit, i.e., articulatory hastening. It is the aim of the present study to investigate the contribution of speech hastening to oral diadochokinesis in the presence of internal and external cues. By means of an optoelectric movement analysis system, the displacements of the lips during repetitions of the syllable /pa/ were recorded in two akinetic-rigidPD individuals. Subjects were asked to synchronize labial diadochokinesis to sequences of periodic acoustic stimuli (2.5–6 Hz). One of the PD patients showed speech hastening, i.e., he produced repetitions of 8 to 9 Hz whenever stimulus frequencies exceeded 4 Hz. The other Parkinsonian adequately matched the stimulus frequencies required. However, she achieved a higher diadochokinesis rate in the matching task than under the instruction to repeat ‘‘as fast as possible.’’ Thus, the presence of an external cue improved performance. In conclusion, our data indicate two deficits of the temporal control of repetitive articulatory gestures in PD: speech hastening and impaired self-paced sequencing. These two pathomechanisms may allow to reconcile the controversial findings on oral diadochokinesis in PD reported so far.
Research Interests:
Nine young infants were followed longitudinally from 4 to 15 months of age. We recorded early spontaneous movements and reaching movements to a stationary target. Time-position data of the hand (end-point), shoulder, and elbow were... more
Nine young infants were followed longitudinally from 4 to 15 months of age. We recorded early spontaneous movements and reaching movements to a stationary target. Time-position data of the hand (end-point), shoulder, and elbow were collected using an opto-electronic measurement system (ELITE). We analyzed the endpoint kinematics and the intersegmental dynamics of the shoulder and elbow joint to investigate how changes in proximal torque control determined the development of hand trajectory formation. Two developmental phases of hand trajectory formation were identified: a first phase of rapid improvements between 16 and 24 weeks of age, the time of reaching onset for all infants. During that time period the number of movement units per reach and movement time decreased dramatically. In a second phase (28-64 weeks), a period of "fine-tuning" of the sensorimotor system, we saw slower, more gradual changes in the endpoint kinematics. The analysis of the underlying intersegmental joint torques revealed the following results: first, the range of muscular and motion-dependent torques (relative to body weight) did not change significantly with age. That is, early reaching was not confined by limitations in producing task-adequate levels of muscular torque. Second, improvements in the endpoint kinematics were not accomplished by minimizing amplitude of muscle and reactive torques. Third, the relative timing of muscular and motion-dependent torque peaks showed a systematic development toward an adult timing profile with increasing age. In conclusion , the development toward invariant characteristics of the hand trajectory is mirrored by concurrent changes in the control of joint forces. The acquisition of stable patterns of intersegmental coordination is not achieved by simply regulating force amplitude, but more so by modulating the correct timing of joint force production and by the system's use of reactive forces. Our findings J. Konczak (~) 9 M. Borutta 9 H. support the view that development of reaching is a process of unsupervised learning with no external or innate teacher prescribing the desired kinematics or kinetics of the movement.
Research Interests:
This experiment studied the effect of imposed optic flow on human locomotion. Six young and 6 older adults were exposed to various patterns of optic flow while walking in a moving hallway. Results showed few cases of impaired postural... more
This experiment studied the effect of imposed optic flow on human locomotion. Six young and 6 older adults were exposed to various patterns of optic flow while walking in a moving hallway. Results showed few cases of impaired postural control (staggers, parachute reactions). No falls were recorded. Kinematic patterns of gait were altered when vision was absent or inconsistent optic flow was presented: Ninety two percent of the subjects mean step velocity differed from their step velocities under normal vision. Compared with imposed central flow, peripheral optic flow was not dominant in inducing kinematic changes. Characteristic gait profiles were obtained, depending on flow direction. Global backward flow tended to slow down step velocity, whereas subjects’ step velocity increased during conditions of forward flow. The results suggest that subjects attempted to match their own walking speed to the velocity of the moving visual scenes. It is concluded that in an uncluttered environment, imposed optic flow has a modulating rather than a destabilizing effect on human locomotion.