Vigilance during sleep

Abstract

Experiments were conducted to examine vigilance during sleep and to test some aspects of Snyder's (1966) theory of dreaming. This theory suggests that the function of Rapid Eye Movement (REM) sleep is to activate the organism and produce a sentinel awakening at the end of the REM period for the purpose of vigilance.

Evidence was found that alert wakings occurred in human Ss throughout sleep from all types of sleep. The rate of waking was highest in REM sleep and a majority of the awakenings from REM sleep occurred at the end of periods of REM sleep. Awakening latency in REM sleep was significantly less than in stage 2 when using an overt response criterion of waking. This was not true however for an EEG criterion of awakening. This supports the notion that during REM sleep, response threshold rather than perceptual threshold, is reduced when compared with stage 2.

Studies of performance after arousal indicated that, on some tasks, performance after REM sleep was superior to trials after stage 2 sleep. However, the differences in performance were small when time of night effects were controlled, performance after REM sleep was superior to trials after slow wave sleep, hut the differences were not as large as had been expected.

The short awakening latency in REM sleep and better performance after REM sleep supports Snyder's notion that REM sleep provides activation in preparation for vigilant "behaviour. The data on spontaneous awakenings also support his suggestion that an important aspect of the REM sleep phenomenon is the "brief awakening that occurs at the end of REM sleep.

While several aspects of Snyder's theory are supported, the results are significant rather than overwhelming, and one is left with the impression that human REM sleep is not completely explained by a vigilance model.