FREQUENCY-SPECIFIC EFFECTS OF MILLIMETER-WAVELENGTH ELECTROMAGNETIC-RADIATION IN ISOLATED NERVE

Effects of low-intensity millimeter waves (MMW) were studied in isolat ed frog nerve using a high-rate stimulation (HRS) functional test. Irr adiation was performed in 3 frequency bands (41.14-41.54, 45.89-45.93, and 50.8-51.0 GHz), at 5 frequencies in each band. The incident power density was 2.5 mW/cm(2) for the 45.89-45.93 GHz band and 10-fold les s 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 relat ive refractory period, 9 ms after the first one. HRS caused a temporar y 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 potentia l (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 GH z. A 100-MHz deviation from this frequency (to 41.24 or 41.44 GHz) red uced the effect more than twofold, and a 200-MHz deviation eliminated it. The results provided further evidence for the existence of frequen cy-specific, resonance-type mechanisms of MMW interaction with biologi cal systems.