Figure 1. Typical nocturnal profiles (from top to bottom) of sleep and plasma concentrations of cortisol and growth hormone (GH). Additionally, the two bottom panels show associated profiles of plasma concentrations of epinephrine and norepinephrine. Abscissa - time of day; ordinate for sleep profile indicates sleep stages: W - wake, REM - rapid eye movement sleep, S1, S2, S3, S4 - sleep stages 1-4, M - movements. S3+S4 represents slow wave sleep (SWS). Note, first half of sleep is dominated by SWS, whereas in the second half REM sleep is dominant. Note also, minimum cortisol concentration and maximum GH concentration during early sleep and a reversed pattern during late sleep. Epinephrine and norepinephrine concentrations are generally lowered during sleep, and particularly during REM sleep epochs (the timing of which is indicated by additional hatched bars).