Age differences in the spontaneous termination of sleep

The stage from which the spontaneous ending of sleep occurred was investiga ted in 138 sleep episodes obtained from 14 younger (19-28 years) and 11 old er (60-82 years) individuals. The possible influences of circadian phase an d quality of the preceding sleep period, as well as the impact of aging on characteristics of sleep termination were examined. Under experimental cond itions in which subjects were isolated from time cues, and behavioral optio ns 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 g roups, younger subjects awakened preferentially from REM while older subjec ts did not. Of the sleep episodes obtained from older subjects, those with sleep efficiencies higher than the median were more likely to terminate fro m REM than those with lower sleep efficiencies. For all subjects, the REM e pisodes from which sleep termination occurred were truncated relative to th ose that did not end the sleep period. In addition, nonterminating REM epis odes 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 th ere are age-related differences in the sleep stage from which spontaneous a wakenings occur, and that these differences may be due in part to the quali ty of the sleep period preceding termination. Findings regarding the charac teristics of both terminating and nonterminating REM episodes are consisten t with the notion that the neural and biochemical context of REM sleep may facilitate a smooth transition to wakefulness. It is speculated that age-as sociated changes in sleep continuity may render unnecessary the putative ro le of REM sleep in providing a 'gate' to wakefulness.