NIGHTTIME DROP IN BODY-TEMPERATURE - A PHYSIOLOGICAL TRIGGER FOR SLEEP ONSET

Relationships between changes in the slope of the body temperature (BT ) and the initiation of sleep were examined in 44 subjects ranging fro m 19 to 82 years of age. Following an adaptation night, subjects remai ned in the laboratory for a baseline night and 72 hours in temporal an d social isolation, with strictly limited behavioral options (''disent rainment'') during which continuous electroencephalograph (EEG) and BT were recorded. Poly somnographic sleep variables (e.g. sleep onset, p ercentage of each sleep stage) were determined for nighttime sleep per iods at baseline and during the disentrainment period. Periods of the BT curve surrounding these sleep bouts were examined for minute to min ute changes, and the time at which the maximum rate of decline (MROD) in temperature occurred was compared with the time of sleep onset (SO) and sleep quality parameters. On the baseline night, the MROD occurre d, on average, 60 minutes prior to SO. During disentrainment, the MROD occurred, on average, 44 minutes prior to SO. The proximity of MROD t o SO did not affect subsequent sleep quality on the baseline night, bu t during disentrainment, there were significant correlations between t he interval from MROD to sleep onset and the amount of slow-wave sleep (SWS) obtained during the sleep bout. There were no significant age d ifferences on variables related to MROD on baseline night, but the tim ing of both MROD and SO were significantly advanced in older, relative to younger, subjects during the disentrainment period. It is suggeste d that a rapid decline in core body temperature increases the likeliho od of sleep initiation and may facilitate an entry into the deeper sta ges of sleep.