Changes in sleep cycle patterns with age.

Abstract An analysis of data by sleep cycle was carried out for the main variables concerning sleep with EEG slow waves (SSW), sleep with rapid eye movements, and awakenings. Data were presented for six age groups with mean ages of 7·4, 13·8, 21·6, 31·5, 55·3, 77·3 yr. While these data represent the first detailed statistical description of cycle changes with age, the results obtained are consistent with earlier observations. For SSW pronounced age changes occured in the first cycle; durations and rates of change across cycles 2–5 were highly similar for all six age groups. The changes with age in cycle 1 were attributed to the changing level of stage 4 EEG with age. Except for the oldest group, SREMP durations increased from cycle 1 to cycle 3, after which there was little change. In elderly subjects, the first SREMP was equal in length to succeeding periods. The trends across the night for eye movement activity were similar to those for SREMP duration; i.e., these trends showed increases from the first to third cycle for all groups except the oldest. It was suggested that the trends in sleep pattern across the night have significant implications for the brain processes which underlie the electrophysiological manifestations of sleep. A speculative hypothesis was advanced to account for the cyclical nature of sleep, the trends in cycles across the night, and the effects of age on these variables. This hypothesis proposes that the function of sleep with rapid eye movements is to provide a substrate or co-factor required to promote maximal occurrence of sleep with slow waves. Many data in the literature may be viewed as consistent with this hypothesis.