Evidence for Circadian Influence on Human Slow Wave Sleep During Daytime Sleep Episodes

Abstract

The occurrence of slow wave sleep within spontaneously initiated daytime sleep episodes was studied to examine hypothesized associations with prior wakefulness and circadian factors. There was a strong relationship between measures of slow wave sleep and the proximity of sleep episodes to the maximum of body core temperature. Those sleep episodes that began within 4 hours of the maximum in body core temperature contained significantly more slow wave sleep than did all other daytime sleep periods, approximating proportions typical of nocturnal sleep. Multiple regression analysis revealed no relationship between measures of slow wave sleep and prior wakefulness. These findings are consistent with an hypothesized approximately-12-hour rhythm in the occurrence of slow wave sleep and they underscore the influence imposed on human sleep by the endogenous circadian timing system. DESCRIPTORS: Circadian rhythms, Slow wave sleep, Prior wakefulness, Naps, Body core temperature.Slow wave sleep (SWS) propensity has long been associated with the duration of prior wakefulness and of subsequent sleep. In an early study of the factors influencing SWS measures, Webb and Agnew (1971) concluded that the amount of Stage 4 sleep that occurred during the first 3 hours of a sleep episode was primarily determined by the duration of prior wakefulness. With increasing time asleep, the amount of Stage 4 sleep declined. More recently, it has been reported that prior wakefulness may account for up to 91% of the variance in SWS amounts recorded in subsequent sleep episodes, and that time asleep may account for up to 96% of the variance in the exponential decline of slow wave sleep across a sleep episode (Knowles, MacLean,

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