Slow waves in the sleep electroencephalogram after daily torpor are homeostatically regulated

Animals emerging from hibernation or daily torpor show an initial increase in electroencephalogram slow-wave activity (SWA, power density between 0.75 and 4.0 Hz) in non-REM sleep, which subsequently declines. These typical f eatures of sleep following prolonged waking led to the interpretation that the animals incur a sleep deprivation (SD) during torpor. This hypothesis h as recently been questioned because the increase in SWA disappears in groun d squirrels when sleep deprived immediately following hibernation. Here we show that in Djungarian hamsters subjected to SD immediately after daily to rpor a predictable increase in SWA occurs during recovery. This supports th e notion that the hamsters must sleep to dissipate the pressure for SWA inc urred during torpor. The similarity between sleep after waking and torpor m ay provide a key for understanding sleep regulation. NeuroReport 11:881-885 (C) 2000 Lippincott Williams & Wilkins.