Sharp and sleepy: evidence for dissociation between sleep pressure and nocturnal performance.

While sleep restriction decreases performance, not all individuals are equal with regard to sensitivity to sleep loss. We tested the hypothesis that performance could be independent of sleep pressure as defined by EEG alpha-theta power. Twenty healthy subjects (10 vulnerable and 10 resistant) underwent sleep deprivation for 25 h. Subjects had to rate their sleepiness (Karolinska Sleepiness Scale) and to perform a 10-min psychomotor vigilance task (PVT) every 2 h (20:00-08:00 hours). Sleep pressure was measured by EEG power spectral analysis (alpha-theta band 6.0-9.0 Hz). Initial performance, EEG spectral power and KSS score were equal in both groups (ANOVA, NS). The performance of vulnerable subjects significantly increased during the night (rANOVA, P < 0.01), whereas resistant subjects globally sustained their performance. Homeostatic pressure and subjective sleepiness significantly increased during the night (rANOVA, P < 0.01) identically in both categories (rANOVA, NS). Resistant subjects sustained their reaction time independently of the increase in homeostatic pressure. The phenotypic determinants of vulnerability to extended wakefulness remain unknown.