THERMOREGULATORY FUNCTION OF SLOW-WAVE SLEEP AND REM SLEEP

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The project is designed to investigated basic biological functions of sleep and sleep stages. Sleep, like torpor, may serve to conserve energy by inhibiting behavioral responses to environmental stimuli and by lowering the regulated level of body temperature and metabolism. Such repeated small savings in energy expenditure could enhance an animal's chance of survival in environments with marginal energy resources. Most investigators have focused on energy conserving aspects of slow wave sleep, which appears to be associated with a temperature-lowering mechanism. Current dogma is that thermoregulation is suspended during REM sleep. However, considerable energy is expended by the brain during REM sleep, and it seems unlikely that this expenditure serves no useful purpose. We hypothesize that REM sleep serves to generate heat locally in the brain and the eyes in order to maintain CNS temperature within acceptable limits while the rest of the body cools during sleep. Heat production is accomplished by 1) increased brain metabolism and 2) rapid eye movements. Maintenance of brain temperature may 1) facilitate rapid arousal from sleep and/or 2) protect CNS tissue in homeotherms from functional or structural impairment during the considerable body cooling which occurs when they sleep in a natural environment. The purpose of this project is 1) to document changes in somatic and CNS temperature during the different stages of sleep by measuring sleep EEG and rectal, chest, finger, eyelid, forehead and tympanic membrane temperatures continuously during sleep, and during voluntary rapid eye movements during wakefulness and 2) to test the hypothesis that REM sleep maintains brain temperature during body cooling by testing the response of REM sleep generating mechanisms to thermal challenges administered to the sleeping brain. During slow wave sleep, we found that rectal, forehead, eyelid and tympanic temperatures decline rapidly. During the first REM sleep episode and during voluntary rapid eye movements during wakefulness, we fund that rectal temperature (a measure of somatic temperature) continues to decline, but that forehead, eyelid, and tympanic temperatures (indirect measures of CNS temperature) rise. These descriptive observations are in accord with our model of selective brain thermogenesis during REM sleep. We have begun the effects of facial heating and cooling on REM sleep generating mechanisms. Data from these experiments have not yet been analyzed.