Dissimilarity of slow-wave activity enhancement by torpor and sleep deprivation in a hibernator

Sleep regulation processes have been hypothesized to be involved in function and timing of arousal episodes in hibernating ground squirrels. We investigated the importance of sleep regulation during arousal episodes by sleep deprivation experiments. After sleep deprivation of 4, 12, and 24 h, starting 4 h after onset of euthermy, a duration-dependent enhancement of slow-wave activity (SWA) of the cortical electroencephalogram during non-rapid eye movement sleep was found, as expected for normal sleep regulation. When sleep deprivation was applied during the initial phase of the arousal episode, in which effects of prior torpor were present in undisturbed recordings, no subsequent recurrence of SWA was found. In addition, prior torpor induced a reduction in the spectral activity of the sigma frequency range (7-14 Hz), which was not observed after sleep deprivation. The effects of torpor and sleep deprivation on subsequent SWA appear qualitatively different. This indicates that effects of deep torpor on sleep are dissimilar to normal sleep regulation.