Do people who sleep more than average have better memory?

In search of answers on many questions that pop into my mind, I came across Quora. This is a great Q(uestions)&A(nswer) site on a wide range of interesting topics. Although I’ve only answered two questions, I want to share this great site with you and my answer on the following question. Some part of the circadian and homeostatic regulation probably sounds familiar for those who read my blog before, so for a more directed answer on the question, scroll down.

Question: Do people who sleep more than average have better memory?

My answer:

If you sleep “more” than average this doesn’t mean this will result in a better memory. Just like many other physiological aspects of our body, the body strives to an equilibrium or homeostasis. It’s the same with sleep. There’s a build up of sleep pressure during wakefulness, and a decrease of sleep pressure when you go to sleep. In addition recovery sleep after a night of sleep deprivation results in an increase in the so-called slow wave activity or “deep sleep” in the first hours of recovery sleep, thus characterizing this homeostatic regulation.

So there is a homeostatic principle (in addition to a circadian mechanism that has a 24 hour rhythm) that regulates our sleep. How fast this sleep pressure builds up and decreases, as well as the length of your circadian rhythm (it can deviate from 24 hours), and maybe other factors as well that at this point I’m not aware of, will determine the amount of sleep you need.

If you deviate from this equilibrium, this can result in detrimental effects on cognitive function as well as physical and mental health. Even sleeping too long is associated with negative outcomes, although it’s hard to infer if this is a causal aspect.

To address your question specifically. No, people who sleep “more than average” will not show an increase in memory function. There is no additional benefit in sleeping extra than the amount needed homeostatically speaking. One of the major functions that has been proposed for sleep is its role in memory consolidation, in the form of so called memory replay. This memory consolidation is thought to take place during the slow wave activity or deep sleep (although it’s also claimed that the transitions between NREM-REM sleep could play a role, or specific neuronal activity like spindles, although I won’t elaborate on this). However, slow wave activity or deep sleep takes place when sleep pressure is high, so during the first part of sleep. When you sleep longer your sleep pressure won’t be high anymore, thus sleep will be more “superficial”, with no more deep sleep and thus no more additional benefit for memory.

This doesn’t implicate however that the first part of sleep is enough. The complete (usually 8h long) sleep episode has a restorative function (and other functions as well of which many still need to be explored), so other aspects like vigilance (or your amount of wakefulness) will affect your functioning during the day and can indirectly affect memory function and cognition. It also depends on the direction you want to look into memory and sleep, e.g. sleep and memory consolidation following learning, or the ability to learn new things after a night of sleep…

Good review article (not free):
Diekelmann, S. & Born, J. The memory function of sleep. Nature Reviews Neuroscience 11, 114–126 (2010).
http://www.nature.com/nrn/journal/v11/n2/abs/nrn2762.html

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