The Displacement of Stages 4 and Rem Sleep Within a Full Night of Sleep

Stage 4 typically occurs dominantly in the first third of a normal night of sleep and REM sleep occurs dominantly in the last third of the night. In this experiment conditions were imposed to prevent these stages from occurring at their usual peak periods. Stage 4 sleep was permitted to occur only during the last two hours of sleep and REM was permitted to occur only during the first two hours of sleep. The results show that each stage can be partially displaced to the peak period of the other, but that stage 4 sleep is elicited more readily late in the sleep period than is REM early during the night.