SLEEP RESTRICTION AND SWS-SUPPRESSION - EFFECTS ON DAYTIME ALERTNESS AND NIGHTTIME RECOVERY

This study evaluated the effects of sleep curtailment and SWS-suppress ion, respectively, on daytime alertness and subsequent night sleep. Se ven subjects participated in four conditions: an undisturbed 8-h sleep (8U; 23.00-07.00 hours), an undisturbed 4-h sleep (4U; 03.00-07.00 ho urs), a 4-h sleep (4D; 03.00-07.00 hours) that was acoustically distur bed when delta waves appeared, and a condition with no sleep (0). Subj ective sleepiness, sleep latency, and simple reaction time (RT) were m easured. In addition, sleep quality was rated. 4D contained 50% of the SWS (as well as spectral slow-wave energy; SWE) compared to 8U, where as the curtailment to 4-h did not significantly decrease SWS. 4D had l ower subjective quality than the other two sleeps. The main difference in daytime sleep latency was between the 8U and the 0 conditions. Rat ed alertness was highest after the 8U sleep. The two 4-h sleeps did no t differ significantly with respect to rated sleepiness or sleep laten cy. However, the effects of the 4U sleep were closer to those of the 8 U sleep and the effects of the 4D sleep were closer to those of the no sleep condition. RT performance was significantly better during the 8 U condition. Recovery sleep after 4D sleep contained significantly mor e SWS than recovery after 4U and 8U. The effects on SWE during recover y were less clear. It was concluded that sleep duration might be more important for daytime alertness than SWS content and that loss of SWS during one night is recovered during the following night.