ABSTRACT
Hibernation is organized in bouts which are discrete episodes of decreased activity, metabolism, and body temperature. The lengths of hibernation bouts depend on various factors including species, body weight, ambient temperature, and time of year. The nature of hibernation bouts has been an enduring question. Most often this question has been framed in terms of the function and the control of periodic arousals. A number of studies of the timing of entrances into and arousals from hibernation have suggested that periodic arousals from hibernation are controlled in part by the circadian system. The circadian studies leave open the questions of why temperature influences the number of circadian cycles expressed in each bout, and what is the function of periodic arousals. electroencephalogram studies of golden-mantled ground squirrels entering hibernation revealed that they were predominantly in non-rapid eye movement sleep with rapid eye movement sleep progressively decreasing until it was not evident at all below a brain temperature of 27 °C.
