The timing of bedtime and waketime decisions in free-running subjects.
Twelve "free-running" temporal isolation studies were performed using healthy human subjects aged 20-81 years (4 males, 8 females). Circadian rhythms were measured in subjective alertness (using a visual analogue scale technique) and rectal temperature. In all 12 subjects best fitting rhythm period were found to be shorter for rectal temperature (mean = 24.3 hours) than for subjective alertness (mean = 24.8 hours). Both rhythms were predictive of bedtime and waketime decisions. Bedtime decisions tended to cluster on the falling arm of the temperature and alertness cycles (modal times = 120 degrees (temperature) and 140 degrees (alertness) after acrophase); waketime decisions on the rising arm (modal times = 240 degrees (temperature) and 300 degrees (alertness) after acrophase). When this pattern was violated, sleep episodes were significantly more variable in length and disturbed by intruding wakefulness.
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D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001143:Arousal; D001833:Body Temperature Regulation; D002940:Circadian Rhythm; D003657:Decision Making; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D012894:Sleep Stages; D014851:Wakefulness