THE RHYTHMS OF HUMAN SLEEP PROPENSITY AND CORE BODY-TEMPERATURE

Evidence from human free-running studies has suggested a close relatio nship between the timing of the circadian rhythm of core body temperat ure and the rhythm of sleep propensity. However, this relationship may be questioned by variations of sleep and wakeful activity which could have masked the endogenous temperature rhythm. A constant routine was used here to 'unmask' the endogenous temperature rhythm in addition t o frequent sleep trials across a 24-h period to confirm the relationsh ip between temperature and sleep propensity rhythms. Of the 14 healthy , good sleeping subjects 13 had significant 24-h cosine rhythms of sle ep propensity;,Eight of these also had a significant 12-h cosine rhyth m. The eight subjects with both-24-h and 12-h rhythms showed a minor p eak of sleep propensity in the early afternoon followed by a trough in the early evening (20.00 hours). Sleep propensity then rose rapidly a t about midnight to a major peak in the early morning. This was follow ed by a second trough of sleep propensity in the late morning. The ave rage times of the sleep propensity phases relative to the circadian te mperature rhythm were very similar to the earlier free-running studies . Furthermore, the times of the sleep propensity phases were highly co rrelated with the body temperature minimum. These results suggested th e possibility that a common oscillator determines the timing of both t he body temperature rhythm and the phases of the sleep propensity rhyt hm.