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. 2004 Sep 25;329(7468):724–728. doi: 10.1136/bmj.329.7468.724

Fig 1.

Fig 1

Sleep stage recording from a normal polysomnogram. This record shows the normal cyclical alternation of sleep stages over the course of the night. Purple bars indicate rapid eye movement (REM) sleep. Note the decreasing amounts of slow wave sleep (SWS) and increasing amounts of REM sleep over the course of the night