The time course of slow wave sleep and REM sleep in habitual long and short sleepers: effect of prior wakefulness.

Three groups of young good sleepers were selected according to their habitual sleep length as short (SS), regular (RS), or long (LS) sleepers. Their sleep was recorded in three situations: reference nights, a recovery sleep night after 36 h of sleep deprivation, and a sleep night after a morning sleep recovery from sleep deprivation (12 h waking time). Total and cycle-by-cycle amounts of slow wave sleep (SWS) and REM sleep were studied both as a function of experimental conditions and of the group of subjects. In all three conditions, LS had less SWS than other sleepers while the differences in SWS amounts between groups were mainly due to different amounts in the second and third cycles, differences between conditions essentially due to variations of SWS within sleep cycle 1 (SWS1). SWS1 appeared to reflect some physiological process whose level increases during waking and declines during sleep. REM sleep proved to be proportional to sleep length.