Dynamic Contributions of Slow Wave Sleep and REM Sleep to Cognitive Longevity

Abstract

Purpose of review: The purpose of this paper was to address how sleep changes with aging, with the broader goal of informing how REM sleep and slow wave activity mechanisms interact to promote cognitive longevity.

Recent findings: We conducted novel analyses based on the National Sleep Research Resource database. Over approximately five years, middle-to-older aged adults, on average, showed dramatically worse sleep fragmentation, a steady decrease in slow wave sleep, and yet a small increase in REM sleep. Averaging across participants, however, masked a major theme: Individuals differ substantially in their longitudinal trajectories for specific components of sleep. We considered this individual variability in light of recent theoretical and empirical work that has shown disrupted sleep and decreased slow wave activity to impair frontal lobe restoration, glymphatic system functioning, and memory consolidation. Based on multiple recent longitudinal studies, we contend that preserved or enhanced REM sleep may compensate for otherwise disrupted sleep in advancing age.

Summary: The scientific community has often debated whether slow wave activity or REM sleep mechanisms are more important to cognitive aging. We propose that a more fruitful approach for future work will be to investigate how REM and slow wave processes dynamically interact to affect cognitive longevity.

Keywords: National Sleep Research Resource; dementia; memory consolidation; older adults; sequential hypothesis; sleep spindles.

Figure 1.. Longitudinal Changes in Total Sleep Time (A), Wake After Sleep Onset (B), Slow Wave Sleep (C) and REM sleep (D) in the Sleep Heart Health Study.

Each line represents one participant’s change in sleep from visit 1 to visit 2. The pre-to-post increase in total sleep time was significant but small, t(2642) = 3.12, p = .002, d = 0.06, whereas the increase in wake after sleep onset was large, t(2642) = 20.63, p < .001, d = 0.40. SWS declined over time by 9.0%, t(2642) = 8.51, p < .001, d = 0.17, whereas REM sleep actually increased over time by 3.6%, t(2642) = 3.99, p < .001, d = 0.08 (greater age at visits 1 and 2 was cross-sectionally associated with decreased REM, rs = −.220 and −.295).

Figure 1.. Longitudinal Changes in Total Sleep Time (A), Wake After Sleep Onset (B), Slow Wave Sleep (C) and REM sleep (D) in the Sleep Heart Health Study.

Each line represents one participant’s change in sleep from visit 1 to visit 2. The pre-to-post increase in total sleep time was significant but small, t(2642) = 3.12, p = .002, d = 0.06, whereas the increase in wake after sleep onset was large, t(2642) = 20.63, p < .001, d = 0.40. SWS declined over time by 9.0%, t(2642) = 8.51, p < .001, d = 0.17, whereas REM sleep actually increased over time by 3.6%, t(2642) = 3.99, p < .001, d = 0.08 (greater age at visits 1 and 2 was cross-sectionally associated with decreased REM, rs = −.220 and −.295).

Figure 1.. Longitudinal Changes in Total Sleep Time (A), Wake After Sleep Onset (B), Slow Wave Sleep (C) and REM sleep (D) in the Sleep Heart Health Study.

Each line represents one participant’s change in sleep from visit 1 to visit 2. The pre-to-post increase in total sleep time was significant but small, t(2642) = 3.12, p = .002, d = 0.06, whereas the increase in wake after sleep onset was large, t(2642) = 20.63, p < .001, d = 0.40. SWS declined over time by 9.0%, t(2642) = 8.51, p < .001, d = 0.17, whereas REM sleep actually increased over time by 3.6%, t(2642) = 3.99, p < .001, d = 0.08 (greater age at visits 1 and 2 was cross-sectionally associated with decreased REM, rs = −.220 and −.295).

Figure 1.. Longitudinal Changes in Total Sleep Time (A), Wake After Sleep Onset (B), Slow Wave Sleep (C) and REM sleep (D) in the Sleep Heart Health Study.

Each line represents one participant’s change in sleep from visit 1 to visit 2. The pre-to-post increase in total sleep time was significant but small, t(2642) = 3.12, p = .002, d = 0.06, whereas the increase in wake after sleep onset was large, t(2642) = 20.63, p < .001, d = 0.40. SWS declined over time by 9.0%, t(2642) = 8.51, p < .001, d = 0.17, whereas REM sleep actually increased over time by 3.6%, t(2642) = 3.99, p < .001, d = 0.08 (greater age at visits 1 and 2 was cross-sectionally associated with decreased REM, rs = −.220 and −.295).

Figure 2.. Novel Analyses of the Changes in SWS and REM Sleep in the Sleep Heart Health Study.

Difference scores represent how much SWS and REM sleep were lost over approximately 5 years, with the correlation of loss being significant, but modest in size (r = .20, p < .001, R² = .04). The effect size remained the same (r = .20) when controlling for chronological age. Highlighted in green are individuals whose SWS declined, but who showed an increase in REM sleep, which we theorize reflects compensation and should promote cognitive preservation. Highlighted in red are individuals who showed declining SWS, without any REM compensation, which we theorize should lead to cognitive decline and dementia. Increased SWS in the presence of increased/decreased REM is likely also relevant, and perhaps reflecting increases/decreases in exercise, diet, social/cognitive engagement, or other resiliency factors [79].