The influence of prior wakefulness on REM sleep.

Data from studies of naps and of shifted sleep were used to determine the relationship between two measures of rapid eye movement (REM) sleep (percentage of REM in the first 2 hr of sleep and REM latency) and prior wakefulness. For each sample, we calculated the difference between the observed value and that predicted by a cosine function that estimated the circadian rhythm of REM sleep propensity. The difference values were found to correlate reliably with hours and log hours of prior wakefulness. We conclude that while REM sleep is regulated in part by an endogenous circadian oscillator, it is also influenced by the duration of prior wakefulness.