REM sleep anchors memories through its own brain waves
Sleep is not one unified state. While deep sleep gets most of the attention in memory research, REM sleep turns out to have its own distinct mechanism for storing memories. Researchers found specific brain oscillations active only during REM sleep that work differently from all previously known sleep-based memory processes.
In a study published in eLife, researchers implanted electrodes in the prefrontal cortex and hippocampus of rats. These two brain regions collaborate in storing memories of spatial experience. During REM sleep, the phase characterised by rapid eye movements, they discovered chains of high-frequency oscillations (HFOs) in the prefrontal cortex that had not been described before.
Two sleep stages, two memory strategies
These REM oscillations turned out to work differently from known memory processes during deep, non-REM sleep. During non-REM sleep, broad activation bursts fire many neurons simultaneously. During REM, reactivation is sparse: only small groups of neurons become active, at specific moments, against a background of local suppression. The researchers suggest both systems complement each other in memory storage, each via a separate route.
Theta oscillations (slow brain waves typical of REM sleep) and acetylcholine (a signalling molecule in the brain) both play a role. The researchers also built a computational model that reproduced the observed patterns, supporting the mechanistic explanation.
What this means for aging and cognition
For longevity research, the implications are notable. With aging, REM sleep quality declines, and so does memory. If REM sleep has its own active mechanism for memory consolidation, then poor sleep quality in older age is not merely a side effect of aging but potentially a contributing factor in cognitive decline. This is preliminary research in rodents; whether the same applies to humans has not yet been demonstrated. But it offers a concrete starting point for future work on sleep and cognitive aging.
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