The disappearing slow wave activity of hibernators.

High and monotonically declining levels of EEG slow wave activity (SWA) occur following arousal from hibernation. Similar profiles of SWA occur in mammals including humans during sleep following periods of prolonged wakefulness, and have been interpreted as reflecting a homeostatic process regulating NREM sleep. It was proposed that even though hibernation appears to be an evolutionary extension of NREM sleep, the low brain temperatures during hibernation are not compatible with sleep restorative processes, and therefore sleep debt accumulates during hibernation and may be a factor triggering periodic arousal. In the present study, golden-mantled ground squirrels were sleep deprived by gentle handling following arousal from hibernation. If the SWA peaks following bouts of hibernation reflect a homeostatic response to an accumulated sleep debt, sleep deprivation should simply displace the SWA which would then occur, and be augmented, during subsequent sleep. In contrast, when animals were sleep deprived following arousal from hibernation, the anticipated SWA peak did not occur during subsequent sleep. It is suggested that the SWA following arousal from hibernation does not represent homeostatic regulation of NREM sleep, but instead some other neurological process involved in the recovery of brain function from an extended period at low temperature.