Effects of a nocturnal environment perceived as warm on subsequent daytimesleep in humans

We studied the influence of a nocturnal environment perceived as warm on th e subsequent daytime sleep of healthy human subjects (20-25 years old). From 00:00 to 8:00, they were kept awake and exposed to either a thermoneut ral and comfortable (CN) or a warm and uncomfortable (EW) environment, as a ssessed by the predicted mean vote/percentage of persons dissatisfied quest ionnaire (PMV/PPD). The subjects then slept from 8:00 to 14:00 in a thermon eutral environment. Sleep was scored according to the Rechtschaffen and Kal es criteria, Rectal temperature was recorded from 22:00 to the end of the s leep period. Compared to CN, a significant but moderate hyperthermia (0.3-0.4 degrees C) occurred rapidly in EW, and was maintained throughout the night, This mode st difference disappeared during subsequent sleep spent at thermal comfort. Exposure to a warm uncomfortable environment before bedtime significantly increased the duration (+37%) and percentage of rapid eye movement sleep (R EMS). This hypnic response could be due to interactions occurring between thermor egulatory, circadian, and sleep mechanisms, It could also be ascribed to sy nergic actions of the neurophysiological (among others, involving the hypot halamo-pituitary-adrenal axis) and psychological (involving memory processi ng) processes developed when the organism faces a moderate stress.