Cortical temperature and EEG slow-wave activity in the rat: analysis of vigilance state related changes

Vigilance states, cortical temperature (TCRT), and electroencephalograph (EEG) slow-wave-activity (SWA, mean power density in the 0.75-4.0 Hz range) of ten rats were recorded continuously during a baseline day, and two recovery days (Recovery 1 and 2) after 24 h of sleep deprivation (SD). The short term changes of TCRT were analysed within episodes of nonrapid eye movement sleep (NREMS), REM sleep (REMS) and waking (W), and at transitions between vigilance states. SWA was analysed within NREMS episodes and at W to NREMS (WN) transitions. TCRT increased during episodes of W and REMS, and decreased during NREMS episodes. These changes were a function of episode duration, and, for W and NREMS, of TCRT at episode onset. In Recovery 1 the increase in TCRT at NREMS to REMS (NR) and NREMS to W (NW) transitions tended to be attenuated. SWA within NREMS episodes was enhanced after SD. Over all experimental days, the increase of SWA and the decrease of TCRT in NREMS episodes were not correlated. It is concluded that during recovery from SD the changes in TCRT at state transitions were little affected. The lack of a relationship between changes in TCRT and SWA indicates that separate mechanisms underlie the regulation of brain temperature and sleep intensity.