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

Abstract

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.

Keywords: intention; older adults; polysomnography; preplay; prospection; rapid eye movement sleep; sleep spindles; slow wave activity; spontaneous retrieval.

Figure 1.

Prospective memory testing procedure. Participants completed three ongoing tasks with a prospective memory or control recognition task embedded. ^aOngoing task order was randomized. ^bProspective memory and control task order were counterbalanced. ^cTarget word set was counterbalanced across conditions.

Figure 2.

Prospective memory performance decreased with increasing age in all ongoing task contexts (category decision, r = −.29, p = .01, lexical decision, r = −.21, p = .07, living/nonliving decision, r = −.39, p < .001). Morning prospective memory performance is the proportion correct averaged for four trials in each of the three contexts. Error bars reflect standard errors.

Figure 3.

Prospective memory consolidation was associated with previous-night REM sleep duration. Prospective memory consolidation is operationalized as the standardized residuals of morning prospective memory performance after adjusting for evening encoding practice block performance.

Figure 4.

REM sleep duration mediated the effect of age on prospective memory. The values are unstandardized regression coefficients (top) and p values (bottom).