The number and duration of the episodes of the various EEG stages of sleep in young and older people.

Episodes of any one electrophysiological sleep stage and of intervening wakefulness were examined as to their numbers and durations in sleep of ten young normal subjects (mean age 22) and in significantly more disturbed sleep of fourteen late middle age normal people (mean age 55). No significant difference between the two age groups was found for any of the stages in the mean number of episodes taken from 4 nights. For any of the stages, the individual numbers of episodes accumulated over the 4 nights varied in a wide range and showed significant consistency with similar data obtained in another set of 4 nights. There were significant differences between the two age groups in episode duration. The sleep of the older group contained significantly higher proportions of longer episodes of wakefulness and drowsiness and significantly lower proportions of longer episodes of slow wave sleep and REM sleep. Thus, the initiation of episodes of EEG stages was on average similar in the better sleep of young and impaired sleep of older subjects, but the maintaining or termination of the episodes were different.