Frequency-Specific Effects of Millimeter-Wavelength Electromagnetic Radiation in Isolated Nerve

Abstract

Effects of low-intensity millimeter waves (MMW) were studied in isolated frog nerve using a high-rate stimulation (HRS) functional test. Irradiation was performed in 3 frequency bands (41.1441.54, 45.89–45.93, and 50.8-51.0 GHz), at 5 frequencies in each band. The incident power density was 2.5 m W/cm² for the 45.8945.93 GHz band and 10-fold less for the other two bands. Each nerve underwent a single 38-min MMW or sham exposure accompanied by an HRS train (20 paired stimuli/s for 17 min). The second stimulus in each pair was delivered during the relative refractory period, 9 ms after the first one. HRS caused a temporary and reversible decrease of the amplitude and conduction velocity of compound action potentials. MMW irradiation attenuated these changes; the MMW effect on the conduction velocity could be caused by microwave heating, while the effect on the amplitude apparently was not thermal. The amplitude changed significantly only in the test action potential (the one evoked during the refractory period), thus testifying to an improvement of the nerve refractory properties. This effect depended on MMW frequency rather than intensity and reached maximum at 41.34 GHz. A 100-MHz deviation from this frequency (to 41.24 or 41.44 GHz) reduced the effect more than twofold, and a 200-MHz deviation eliminated it. The results provided further evidence for the existence of frequency-specific, resonance-type mechanisms of MMW interaction with biological systems.