Intracranial temperature across 24-hour sleep-wake cycles in humans

The 24 h time course of intracranial temperature, recorded subdurally at the parahippocampal gyrus in six patients (19 24 h periods), exhibited a prominent 24 h rhythm with its crest located at 20-21 h. The declining trend of intracranial temperature between lights off and sleep onset persisted in the first nonREM sleep episode (studied in two patients, seven sleep episodes). The correlation between EEG slow-wave activity (SWA) in nonREM sleep and the change in temperature explained < 25% of the variance. Although the change in temperature tended to be more positive in REM sleep episodes than in nonREM sleep episodes, no significant increase was observed in REM sleep. The data indicate that intracranial temperature exhibits a marked 24 h rhythm, the time course of which is only slightly affected by nonREM/REM sleep and EEG synchronization.