Age differences in the spontaneous termination of sleep.

The stage from which the spontaneous ending of sleep occurred was investigated in 138 sleep episodes obtained from 14 younger (19-28 years) and 11 older (60-82 years) individuals. The possible influences of circadian phase and quality of the preceding sleep period, as well as the impact of aging on characteristics of sleep termination were examined. Under experimental conditions in which subjects were isolated from time cues, and behavioral options to sleep were limited, no age-associated differences in the duration of sleep periods, or in the number or duration of REM episodes were observed. Despite similar percentages of NREM (stages 2-4) and REM sleep across age groups, younger subjects awakened preferentially from REM while older subjects did not. Of the sleep episodes obtained from older subjects, those with sleep efficiencies higher than the median were more likely to terminate from REM than those with lower sleep efficiencies. For all subjects, the REM episodes from which sleep termination occurred were truncated relative to those that did not end the sleep period. In addition, nonterminating REM episodes that were interrupted by a stage shift were most often interrupted by brief arousals to stage 0. Such arousals within nonterminating REM episodes occurred, on average, after a similar duration as the terminating point of sleep-ending REM episodes. The results from this study demonstrate that there are age-related differences in the sleep stage from which spontaneous awakenings occur, and that these differences may be due in part to the quality of the sleep period preceding termination. Findings regarding the characteristics of both terminating and nonterminating REM episodes are consistent with the notion that the neural and biochemical context of REM sleep may facilitate a smooth transition to wakefulness. It is speculated that age-associated changes in sleep continuity may render unnecessary the putative role of REM sleep in providing a 'gate' to wakefulness.