ELECTROPHYSIOLOGICAL EVIDENCE SUGGESTING THAT SENSORY STIMULI OF UNKNOWN ORIGIN INDUCE SPONTANEOUS K-COMPLEXES

The present study was performed to determine whether or not spontaneou s K-complexes are induced by sensory stimuli. In the first part of the present study, sound stimuli were prescribed during sleep in 7 health y, young, adult subjects. EEG segments in stage 2 sleep were averaged separately according to the presence or absence of an evoked K-complex appearing after each stimulus. The sound stimulus induced N100 and P2 00 components in averaged EEGs regardless of K-complex appearance. The appearance of N100 and P200 components was considered to be an indica tor of the presence of sensory stimuli. In the second part of the pres ent study, EEG segments in stage 2 sleep containing an evoked K-comple x or spontaneous K-complex were separately averaged with respect to th e peak of N300, one of the main components constituting the K-complex. Small negative and positive components were found just before the mai n components of spontaneous K-complexes in averaged EEGs. These two co mponents were judged to correspond to N100 and P200 components induced by the sound stimulus, as they appeared just before the main componen ts of the spontaneous K-complex with almost the same lag time between the two components, or between each of the two components and the main components of K-complex, as in the case of N100 and P200 appearing ju st before the evoked K-complex. The present findings suggest that the spontaneous K-complex is not a spontaneous phenomenon, but that it is induced by sensory stimuli, probably of extracerebral origin.