[Slow eye movements and transitional periods of EEG sleep stages during daytime sleep]

Slow eye movements (SEMs) were analyzed in 28 young adult females during daytime sleep. Data from transitional periods of each EEG stage were obtained by accumulating its epoch series synchronized to the onset or termination of the other stages. Sleepiness was reported by the subject by pressing a button switch. SEMs were prominent at the transitional period of stage W approaching the onset of stage 1 (sleep tendency). They declined with deepening of sleep at the transitional periods of EEG stages 22 and 2, and disappeared completely during slow wave sleep (SWS) periods. The recovery of SEMs occurred towards awakening at every EEG transitional period except for SWS. The individual difference in the appearance of SEMs was partly explained by a positive correlation with stage 3 latency: the longer the latency was, the larger the mean SEMs. Perceived sleepiness increased in proportion to SEMs during the entry and re-entry periods to sleep. These results suggest that SEMs are strongly associated with a wake-sleep transition.