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Abstract
Much controversy has been focused on the extent to which the amygdala belongs to the autobiographical memory (AM) core network. Early evidence suggested the amygdala played a vital role in emotional processing, likely helping to encode emotionally charged stimuli. However, recent work has highlighted the amygdala's role in social and self-referential processing, leading to speculation that the amygdala likely supports the encoding and retrieval of AM. Here, cognitive as well as structural and functional magnetic resonance imaging data was collected from an extremely rare individual with near-perfect AM, or hyperthymesia. Right amygdala hypertrophy (approximately 20%) and enhanced amygdala-to-hippocampus connectivity (>10 SDs) was observed in this volunteer relative to controls. Based on these findings and previous literature, we speculate that the amygdala likely charges AMs with emotional, social, and self-relevance. In heightened memory, this system may be hyperactive, allowing for many types of autobiographical information, including emotionally benign, to be more efficiently processed as self-relevant for encoding and storage.
Acknowledgments
This work was supported by National Institute on Aging grant R01 AG038471 (BAA), the Vanderbilt University Institute of Imaging Science, and the Vanderbilt University Department of Neurology. The authors are eternally indebted to HK and his grandmother for their patience and willingness to cooperate during the many trips to the laboratory. Also, many thanks to HK's treating physicians; Tom Davis, MD, Jennifer Najjar, MD, and Eric Pina-Garza, MD at Vanderbilt University Hospital for providing insight and verification into HK's history and development. Without the referral from Dr. Davis, this project would never have been completed. We also thank Donna Butler and Victoria Morgan for experimental assistance.