The duration of REM sleep epic, odes in normal sleep

The distributions of the durations of the first 3 REM sleep episodes have been analysed using a total of 134 overnight sleep recordings from 10 subjects. From investigation of the length of uninterrupted episodes of stage REM, it is shown that arousals to stage 0/1 could play an important part in the process of REM exit, and that by the middle of the sleep period, these arousals probably occur according to a Poisson process. During the first and second REM episodes a more complex process appears to be at work, which could reflect increased pressure for slow wave sleep. These findings suggest that the duration of a REM episode is determined by a process that has a large stochastic element, which is not necessarily tied to REM entry.