EFFECTS OF SLEEP ON SOMATOSENSORY-EVOKED RESPONSES IN HUMAN - A MAGNETOENCEPHALOGRAPHIC STUDY

We studied the effects of sleep on somatosensory evoked magnetic field s (SEFs) following median nerve stimulation in normal subjects, to inv estigate the changes of functional processing of sensory perception in the primary and second sensory cortices (SI and SII). The early compo nents, 1M, 2M and 3M, which were generated in SI contralateral to the stimulated nerve, showed no significant change of latency or amplitude in stage 1 or 2 as compared with those in the awake state. The long-l atency response, 4M whose latency was about 100 ms, was significantly enhanced in stage 2. The 4M was considered to be generated in SI and S II in the awake state, but the enhanced 4M in stage 2 was restricted i n SI. The 4M(I) generated in SII of the hemisphere ipsilateral to the stimulated nerve, corresponding to 4M in the contralateral hemisphere, was absent during sleep. These findings were probably due to the diff erence of activities between SI and SII during sleep, that is, an incr ease of sensitivity to somatosensory stimulation in SI but a decrease or disappearance in SII.