title: Circadian and sleep/wake dependent aspects of subjective alertness and cognitive performance.
abstract: Circadian and sleep/wake dependent processes underlying variations in subjective alertness and cognitive performance were assessed in a constant routine protocol and in a protocol in which the sleep/wake cycle was uncoupled from the output of the endogenous circadian pacemaker.  In the latter protocol, the contribution of a sleep/wake dependent process and a circadian process to alertness and performance were separated by folding the data at either the period of the sleep/wake cycle or at the period of the endogenous circadian body temperature rhythm.  This analysis revealed that prior wakefulness within a range of 0-18 h significantly reduced alertness and performance and that the circadian rhythm of core body temperature paralleled the circadian rhythm of alertness and performance.  During the first 16 h of the constant routine protocol, which coincided with the subjects' habitual period of wakefulness, alertness and performance remained at a stable level.  The latter finding was explained by assuming that during our usual waking day the circadian system counteracts the detrimental effects of increasing duration of prior wakefulness.
authors.affiliation: Harvard Medical School, Boston.
authors.forename: D J
authors.initials: DJ
authors.lastname: Dijk
authors.forename: J F
authors.initials: JF
authors.lastname: Duffy
authors.forename: C A
authors.initials: CA
authors.lastname: Czeisler
mesh_terms: D000293:Adolescent; D000328:Adult; D001831:Body Temperature / Q000502:physiology; D002940:Circadian Rhythm / Q000502:physiology*; D003071:Cognition / Q000502:physiology*; D006801:Humans; D008297:Male; D012890:Sleep / Q000502:physiology*; D013997:Time Factors; D014851:Wakefulness / Q000502:physiology*