What’s the evidence for REM being good for memory consolidation?
Q: What’s the evidence for the claim that REM sleep is important for memory consolidation? Although I haven’t looked systematically, it appears that there is no consensus about the purpose of REM sleep.
A: The best evidence for memory consolidation in REM comes from neuroimaging (PET) scans. These snapshots show that brain structures involved with long-term memory and retrieval are actually more active than in waking states. What’s more, the brain’s emotional center (the limbic system) is also highly activated, suggesting that consolidation of emotional memories are especially targeted during REM.The scientific theory that sleep in general benefits memory performance is well established but has changed over the years. For example, early sleep studies claimed that depriving people of REM sleep impairs certain kinds of memory formation, namely declarative memory, the next day. In addition, studies done on insomniacs noticed that REM sleep was seen to correlate with comparatively higher levels of memory consolidation, most likely compensating for lower levels of Deep sleep.
Since then, the best evidence for memory consolidation during REM comes from neuroimaging (PET) scans. These snapshots of the brain show that the brain structures involved with long-term memory and retrieval are actually more active than in waking states. What’s more, the brain’s emotional center is also highly activated, suggesting that consolidation of emotional memories are especially targeted during REM.
However, new evidence indicates that the consolidation of memory also takes place outside of REM sleep. A 2010 study found that subjects who napped AND dreamed of a memory-related task during a non-REM nap–that is, they did not go into REM sleep at all– improved their performance of the task later on.
On top of that, certain features of sleep architecture are now thought to play a role in the overall memory process. Sleep spindles, which typically occur in Light sleep, are now thought to play a role in declarative memory consolidation along with REM.
Finally, hormones are now recognized as an important piece of memory consolidation. Low levels of cortisol–a major stress hormone–are associated with memory consolidation, whereas increased levels impair consolidation. In healthy sleepers, cortisol remains low in the first part of the night–when we have most of our Deep sleep mixed with Light–but tends to increase towards morning.
So while REM sleep is still thought to play an active role in memory consolidation, it’s important to remember that other sleep stages and bodily functions appear to play important roles as well. To ensure that you get the most out of your memories, it’s best to keep yourself in good sleep, physical, and mental health.
Academic References
- Born J, Wagner U. Memory consolidation during sleep: role of cortisol feedback, Annals of NY Academy of Science. 2004 Dec;1032:198-20
- Stickgold, R. How do I remember? Let me count the ways, Sleep Medicine Review. 2009 October; 13(5): 305–308.
- Tamminen J, et al., Sleep spindle activity is associated with the integration of new memories and existing knowledge, Journal of Neuroscience, 2010 Oct 27;30(43):14356-60
- Wamsley EJ, et al., Dreaming of a learning task is associated with enhanced sleep-dependent memory consolidation, Current Biology. 2010 May 11;20(9):850-5
Related Questions
- Are there any associations between insomnia and memory loss?
- How important is Light sleep?
- Is it beneficial or harmful to get more REM and Deep sleep than Light?
- What is stress and how can it affect sleep?
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