REM Density is Dissociated from REM Sleep Timing During Free-Running Sleep Episodes

Sleep patterns of 3 normal male subjects living in an free of time cues were polygraphically recorded for a total of 26 entrained (scheduled 24 hr) and 62 free-running (self-selected) sleep- wake times. An analog tape recorder was used to record electroencephalograms, chin electromyograms, and horizontal electro-oculograms (left outer canthus - right outer canthus; time constant, 3-60 Hz). Eye movements were detected by automatic computing of the local maxima and local minima in the data after it had been filtered and digitized. During entrainment, REM density progressively increased in successive REM episodes, as did mean REM episode duration. The pattern of REM density was not significantly different during freerunning as compared to the entrained condition. In contrast, the timing of REM sleep was significantly different from that observed under the entrained condition. During free-running sleep episodes, there was a more rapid accumulation of REM sleep and an increased duration in earlier REM episodes. This dissociation of eye movement density from the timing of REM sleep suggests that eye movement density and perhaps other phasic REM activity are controlled by a different mechanism than the endogenous oscillator controlling the timing of REM sleep.