DYNAMICS OF THE SLEEP EEG AFTER AN EARLY EVENING NAP - EXPERIMENTAL-DATA AND SIMULATIONS

Increasing sleep pressure is associated with highly predictable change s in the dynamics of the sleep electroencephalogram (EEG). To investig ate whether the effects of reduced sleep pressure also can be accounte d for by homeostatic mechanisms, nighttime sleep following an evening nap was recorded in healthy young men. In comparison with the baseline night, sleep latency in the postnap night was prolonged, rapid eye mo vement sleep (REMS) latency was reduced, and EEG: power density in non -REMS was decreased in the delta and theta band. The buildup of both E EG slow-wave activity (SWA; power density in the 0.75- to 4.5-Hz range ) and spindle frequency activity (SFA; power density in the 12.25- to 15.0-Hz range) in non-REMS episodes was diminished (SWA: episodes 1-3; SFA: episode 1). The typical declining trend of SWA over consecutive non-REM sleep episodes was attenuated. The time course of SWA could be closely simulated with a homeostatic model of sleep regulation, altho ugh some discrepancies in level and buildup of SWA were apparent. We c onclude that homeostatic mechanisms can largely account for the dynami cs of the sleep EEG under conditions of reduced sleep pressure.