Slow waves during dream sleep track forgetting in older adults
Older adults whose rapid eye movement sleep contained more slow waves also forgot more material overnight in a peer-reviewed observational study. The team compared sleep recordings with memory tasks and, in separate subsets, Alzheimer-related markers. The associations concern sleep structure; they do not establish that changing these waves prevents memory loss.
Science··Morning
Slow waves persisted during active REM periods
Slow brain waves persisted during rapid eye movement sleep in older adults, and their density was associated with forgetting across the night. This single peer-reviewed observational study examined the internal structure of REM sleep rather than simply its duration. It distinguished bursts of eye movements, called phasic periods, from quieter tonic periods within the same sleep stage.[1]
The researchers separated fast, sawtooth-shaped delta waves from slower oscillations resembling those of sleep without rapid eye movements. In younger adults, phasic periods brought more fast waves and suppressed slow waves. Older adults showed weaker suppression of the slow waves during those periods. Wave density and its distribution across the scalp were both considered, capturing differences in timing as well as location.[1]
Word-pair tasks measured overnight forgetting
Memory analyses used laboratory sleep recordings and learning tasks from 62 cognitively unimpaired older adults and 15 healthy younger adults in the Berkeley cohort. Participants learned word pairs before sleep and completed recognition testing around the overnight interval. Older participants with denser slow-wave activity during REM retained less of the learned material. The association persisted in analyses adjusting for sex, age and selected measures of slow activity in other sleep stages.[1]
Separate subsets of older participants underwent positron emission tomography, an imaging method used here to estimate amyloid-beta and tau protein burdens. Slow-wave persistence during phasic REM was associated with these Alzheimer-related markers too. The memory, imaging and genetic analyses did not all examine the same participants, so the relationships cannot be treated as one complete chain measured in each person.[1]
A second cohort connected wave patterns with genetic risk
Sleep and genetic data for another 558 adults came from an independent cohort. Some differences associated with aging appeared there too and linked an Alzheimer-risk variant combination of the apolipoprotein E (APOE) gene to fewer fast sawtooth waves. Those participants had suspected untreated sleep-disordered breathing, limiting wider generalization. With no intervention to change the waves, the study establishes associations and does not validate a clinical test for predicting an individual’s future dementia.[1]
