A Continuum of Slow-Wave Sleep and Shallow Torpor in the Pocket Mouse Perognathus longimembris

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Abstract
Electroencephalogram (EEG), electromyogram (EMG), and brain temperature (Tbr) were recorded from seven pocket mice (Perognathus longimembris) during euthermia and 22 bouts of torpor induced by food deprivation. All but one of a total of 22 entrances into torpor began during slow-wave sleep (SWS), and SWS continued throughout 89% of the entrances, whereas rapid eye movement (REM) sleep was almost completely suppressed. Although EEG amplitude diminished as dropped, SWS and wakefulness could still be distinguished at the lowest of 23-25 C. SWS continued to be preponderant, accounting for 96% of the recordings at these . Thus the association of SWS with declines in during entry into hibernation or torpor reported for marmots, squirrels, and doves also applies to one of the smallest mammals. However, suppression of REM sleep during hibernation or torpor is not as great in these larger endotherms as in the pocket mouse. in a euthermic pocket mouse is strongly affected by ambient temperature due to the combination of the large surface-to-volume ratio of its body and the suspension of thermoregulation during REM sleep. Therefore, the disappearance of REM sleep during entry into torpor may represent a homeostatic adjustment effecting continuous regulation of .