Rapid eye movement sleep mediates age-related decline in prospective memory consolidation.

STUDY OBJECTIVES: Prospective memory, or remembering to execute future intentions, accounts for half of everyday forgetting in older adults. Sleep intervals benefit prospective memory consolidation in young adults, but it is unknown whether age-related changes in slow wave activity, sleep spindles, and/or rapid eye movement (REM) sleep mediate hypothesized effects of aging on prospective memory consolidation. METHODS: After an adaptation night, 76 adults aged 18-84 completed two experimental nights of in-laboratory polysomnography recording. In the evening, participants encoded and practiced a prospective memory task and were tested the next morning. On a counterbalanced night, they encoded and practiced a control task, and were tested the following morning. RESULTS: Increasing age predicted worse prospective memory consolidation (r = -.34), even when controlling for encoding, speed, and control-task performance (all ps < .05). Frontal delta power, slow oscillations, and spindle density were not related to prospective memory consolidation. REM sleep duration, however, explained significant variance in prospective memory consolidation when controlling for age (∆R2 = .10). Bootstrapping mediation showed that less REM sleep significantly mediated the aging effect on prospective memory consolidation [b = -.0016, SE = 0.0009 (95% confidence interval [CI] = -0.0042 to -0.0004)]. REM sleep continued to mediate 24.29% of the total effect of age on prospective memory after controlling for numerous demographic, cognitive, mental health, and sleep variables. CONCLUSION: Age-related variance in REM sleep is informative to how prospective memory consolidation changes with increasing age. Future work should consider how both REM sleep and slow wave activity contribute, perhaps in a sequential or dynamic manner, to preserving cognitive functioning with increasing age.

The effects of bedtime writing on difficulty falling asleep: A polysomnographic study comparing to-do lists and completed activity lists.

Bedtime worry, including worrying about incomplete future tasks, is a significant contributor to difficulty falling asleep. Previous research showed that writing about one's worries can help individuals fall asleep. We investigated whether the temporal focus of bedtime writing-writing a to-do list versus journaling about completed activities-affected sleep onset latency. Fifty-seven healthy young adults (18-30) completed a writing assignment for 5 min prior to overnight polysomnography recording in a controlled sleep laboratory. They were randomly assigned to write about tasks that they needed to remember to complete the next few days (to-do list) or about tasks they had completed the previous few days (completed list). Participants in the to-do list condition fell asleep significantly faster than those in the completed-list condition. The more specifically participants wrote their to-do list, the faster they subsequently fell asleep, whereas the opposite trend was observed when participants wrote about completed activities. Therefore, to facilitate falling asleep, individuals may derive benefit from writing a very specific to-do list for 5 min at bedtime rather than journaling about completed activities. (PsycINFO Database Record