Hibernation at moderate temperatures: a continuation of slow wave sleep.

Golden-mantled ground squirrels (Citellus lateralis) displayed virtually continuous electrophysiological states of sleep when hibernating at moderate ambient temperatures (22 degrees C). Rapid-eye-movement sleep progressively diminished with the fall in body temperature so that at a body temperature of 23 degrees C it was completely absent. At this temperature hibernation was characterized by slow wave sleep isomorphic with slow wave sleep episodes at non-hibernating (euthermic) body temperatures.