SLEEPINESS AND SLEEP STATE ON A 90-MIN SCHEDULE

The effects of REM [rapid eye movement] and slow wave sleep (SWS) on subjective sleepiness were studied in 10 subjects placed on a 90 min sleep-wakefulness schedule for either 5 1/3 or 6 (24 h) days. Subjects were permitted to sleep for 30 min periods separated by 60 min of enforced wakefulness. Sleep recordings showed that sleep onset REM periods occurred frequently; REM and SWS appeared during the same sleep period only 27 times; REM sleep tended to occur on sleep periods that alternated with SWS periods. Sleepiness was measured using the Stanford Sleepiness Scale (SSS) given 15 min after before (pre-sleep) and 15 min after (post-sleep) each sleep period. Average SSS ratings showed a 24 h fluctuation in sleepiness. Negative and positive SSS changes tended to alternate with each 90-min period. Significant correlations were found with post-sleep SSS ratings and SWS and with pre-sleep SSS ratings and REM sleep. Differences between pre- and post-sleep SSS scores were also correlated with the sleep states: increased sleepiness was correlated with SWS and decreased sleepiness with REM sleep.