Figure 9.18: Time spent by people of different ages in waking, REM sleep, and NREM sleep . REM sleep occupies about 8 hours a day in newborns but less than 2 hours in most adults. The sleep of infants is not quite like that of adults, however, and the criteria for identifying REM sleep are not the same. (Source: From “Ontogenetic development of human sleep-dream cycle,” by H. P. Roffwarg, J. N. Muzio, and W. C. Dement, Science, 152, 1966, 604–609. Copyright 1966 AAAS. Reprinted by permission.)
The electroencephalograph (EEG) allowed researchers to discover that there are various stages of sleep.
Over the course of about 90 minutes:
a sleeper goes through sleep stages 1, 2, 3, and 4
then returns through the stages 3 and 2 to a stage called Rapid eye movement sleep (REM).
REM are periods characterized by rapid eye movements during sleep where postural muscles of the body are more relaxed than other stages.
Stages other than REM are referred to as non-REM sleep (NREM) .
Fig. 7.6 (a) Average proportion of time adults spend daily in REM sleep and NREM sleep. REM periods add up to about 20 percent of total sleep time. (b) Typical changes in stages of sleep during the night. Notice that dreams mostly coincide with REM periods.