Brief skin temperature changes towards thermoneutrality trigger REM sleep in rats

When rats were in slow-wave sleep (SWS) at an environmental temperature (23°C) below their thermoneutral zone (27–31°C), brief skin warming by either radiant heating, or forced air convection resulted in REM sleep on 79–80% of the trials. During control nonwarmed SWS bouts, the animals went into REM sleep on only 22–24% of the trials. When the environmental temperature was above thermoneutrality, 34°C, lowering skin temperature by convective cooling resulted in REM sleep entry 68% of the time, compared to 21% for noncooled, control trials. Skin warming and cooling at 29°C decreased the percent occurrence of REM sleep to 22% and 9% respectively, for at this thermoneutral temperature 46% of the control SWS bouts ended in REM sleep. Thus, peripheral temperature changes towards thermoneutrality trigger REM sleep in mildly thermally stressed rats.