Experimentally displaced sleep: Effects on sleepiness

Abstract

In order to study the effects of short daytime sleep on sleepiness, 6 healthy male subjects were exposed to 3 experimental conditions — long night sleep (23.00–07.00 h), short night sleep (03.00–07.00 h) and short day sleep (07.00–11.00 h). Sleepiness was measured in 2 h intervals by the EEG-based multiple sleep latency test (MSLT) and self-ratings. The results showed a pronounced circadian rhythmicity with the peak length (lowest sleepiness) in the evening (19.00–23.00 h) and the minimum length (highest sleepiness) in the early morning (05.00 h). Around 15.00 h a secondary (temporary) minimum was found for all 3 conditions. The shortened day sleep began to have effects on sleepiness (shorter latencies) in the afternoon, with a peak around 19.00 h. This effect had the character of a delay of the normal evening rise of latency (alertness). The short night sleep had similar effects. The MSLT covaried moderately with rectal temperature and rated sleepiness (negatively). It was concluded that sleep loss and circadian influences have a combined effect on sleepiness.