RAPID DECLINE IN BODY-TEMPERATURE BEFORE SLEEP - FLUFFING THE PHYSIOLOGICAL PILLOW

A novel approach to the analysis of body core temperature was employed in an effort to further clarify the temporal relationship between the nightly decline in body temperature and the timing of the onset of no cturnal sleep. Core body temperature and EEG sleep recordings were obt ained from 10 healthy elderly subjects while they lived in the laborat ory and self-selected bedtimes and wake-up times. A rate-of-change cur ve was then generated for each temperature data set, showing the relat ive magnitude by which body core temperature declined (or increased) f rom minute to minute across the recording period. The time at which th e maximum rate of decline (MROD) occurred was determined, and this tim e was compared with subjects' self-selected bedtimes and with subseque nt EEG-defined sleep onsets. Eight of the 10 subjects' body temperatur e curves showed a maximum rate of decline well before (mean 41 min) th e decision was made to retire. There was a significant positive correl ation between the amount of wakefulness within the first hour after in itial sleep onset and MROD relative to both bedtime and sleep onset (r (s) = 0.70; p < 0.04). That is, the closer MROD occurred to either bed time or sleep onset, the less wakefulness there was within the first h our after sleep onset. The findings indicate that the process of sleep initiation is most likely to occur when body temperature is declining at its maximum rate and is most successfully accomplished at this pha se of the temperature cycle.