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Sleep and learning

Sleep and Memory: Why Rest Matters for Learning

By LaserMind Team ·

What does sleep do for memory?

A major review of more than a century of research concluded that sleep benefits the retention of memory [4]. Early theories saw sleep as passive, simply protecting new memories from interference. Current theories give it an active role: in the leading account, recently formed memories are reactivated during deep, slow-wave sleep and integrated into long-term memory, and REM sleep may then help stabilise them [4]. The review describes the waking brain as suited to taking in new memories, and the sleeping brain as suited to consolidating them [4].

That account is a model of the mechanism. It explains why sleep might matter, but the practical question is how large the effects are in people. That is what the studies below measured.

A note on numbers: several of these studies report an effect size called g. It expresses the difference between two groups in a standard unit, so that studies with different tests can be combined. Larger numbers mean bigger differences, and a minus sign means the group short of sleep did worse.

Sleep after learning helps you keep it

A 2021 meta-analysis pooled 823 results from 271 groups of participants, reported in 177 articles published between 1967 and 2019 [1]. People recalled more after sleep than after the same amount of time awake: the authors described the average effect as moderate (g = 0.44), and it fell to g = 0.28 once they allowed for possible selective reporting [1]. The benefit was larger when the material had been studied several times rather than once, and larger after natural night-time sleep than after daytime naps [1].

Another 2021 paper pooled studies in which people stayed awake all night after learning [2]. Their memory for the material was worse than that of people who slept (g = 0.28), and the effect was larger when they were tested straight after the sleepless night than when they were tested after catching up on sleep [2].

Sleep before learning helps you take it in

The same paper also pooled studies in which people missed a full night of sleep before learning [2]. Their memory for the new material was worse than that of rested people (g = 0.62) [2].

The authors add two warnings. Both analyses showed signs of publication bias, and statistical power was very low in most of the studies, so the exact sizes of these effects are uncertain [2].

What sleep loss does to attention

A 2010 meta-analysis of 70 articles looked at the effect of up to 48 hours without sleep on six kinds of cognitive task [3]. The effects ranged from large, for lapses in simple attention tasks, to small and not statistically significant, for accuracy in reasoning; complex attention, working memory, processing speed and short-term memory fell between these extremes [3].

A whole night without sleep is not the only concern. A 2017 meta-analysis of 61 studies of sleep restriction, in which people were allowed less sleep rather than none, found a negative effect on cognition overall (g = −0.38) [5]. The effect held for sustained attention (g = −0.41), executive functioning (g = −0.32) and, to a smaller degree, long-term memory (g = −0.19) [5].

Short nights can also add up without your noticing. In a laboratory study of 48 healthy adults aged 21 to 38, spending 6 hours or less in bed each night for two weeks produced cognitive deficits equivalent to up to two nights without any sleep [6]. Yet the participants' ratings of their own sleepiness rose only a little after the first days, which the authors read as a sign that they were largely unaware of how far their performance had dropped [6].

What this means for studying

  • Spread study over several days. That puts nights of sleep between your sessions, and in the meta-analysis the sleep benefit was larger for material studied more than once [1]. Spacing has its own research behind it too: see How to improve memory for studying.
  • Avoid all-nighters, especially before a day of new learning. A sleepless night makes new material harder to remember and attention lapses more likely [2][3].
  • Protect the nights after studying too. Staying awake all night after learning also reduced memory for what was learned [2].
  • Don't rely on feeling fine. In the restriction study, people's sense of sleepiness lagged behind the decline in their performance [6].

For more on why memories fade, and how sleep fits in, see Why do we forget things?

General sleep habits

Expert panels have issued consensus recommendations on how much sleep people need. For adults aged 18 to 60, the American Academy of Sleep Medicine and the Sleep Research Society recommend 7 or more hours a night on a regular basis, and note that individual needs vary [7]. For teenagers aged 13 to 18, the American Academy of Sleep Medicine recommends 8 to 10 hours per 24 hours [8].

Common sleep-hygiene advice covers regular sleep timing, exercise, managing stress, reducing noise, and avoiding caffeine, nicotine, alcohol and daytime naps [9]. A review of this advice found that research generally links each recommendation with night-time sleep, but that their direct effects remain largely untested in the general population, and that sleep hygiene on its own has proved ineffective as a treatment in clinical sleep medicine [9]. Treat these as reasonable general habits, not as a treatment.

When to talk to a doctor. If you often struggle to fall or stay asleep, wake up unrefreshed, or feel very sleepy during the day despite spending enough time in bed, talk to a doctor. Persistent sleep problems can have medical causes that need a proper assessment. The expert consensus also advises people who are concerned that they sleep too little or too much to consult a healthcare provider [7].

What the research says

◆ SupportedSleep after learning improves later recall compared with the same time awake, with a moderate average effect [1]. Up to 48 hours without sleep impairs attention, most of all simple attention [3], and a sleepless night impairs memory for material learned afterwards [2].
◇ ConditionalSleeping less than usual over several nights impairs sustained attention, executive functioning and, to a smaller degree, long-term memory; the effects varied with age group, time of day and the number of restricted nights [5]. The size of the sleep benefit depends on how the material was studied, how memory was tested and what kind of sleep was compared [1].
✕ Not establishedExact effect sizes: signs of publication bias and underpowered studies mean the pooled estimates are uncertain [2]. That any study technique, app or exercise, including LaserMind's, improves sleep or memory consolidation during sleep.

Try it on LaserMind

▶ Recall Cards (spaced repetition)

Review your cards over several days, so there are nights of sleep between sessions.

If you want a quiet routine before bed, the Breath Counter is a short attention exercise. We don't offer it as a sleep aid. The main study behind it validated breath counting as a measure of mindfulness, linked with less mind-wandering, and did not look at sleep [10].

Try it on LaserMind

▶ Breath Counter & Pacer

Count your out-breaths from 1 to 10, and start again when you notice your mind has wandered.

What research has not established

Many of the studies behind these findings took place in laboratories, often with healthy young adults, simple materials such as word lists, and short delays between learning and testing. The sleep-restriction study above, for example, included adults aged 21 to 38 [6]. Results may differ for older adults, for children and teenagers, and for complex material learned over a whole course.

Effect sizes vary. The benefit of sleep depended on how often the material was studied and on how memory was tested [1]. The effects of sleep restriction varied with age group, time of day and the number of restricted nights [5]. The sleep-deprivation studies showed signs of publication bias and very low statistical power [2].

Much of this research keeps people awake for a whole night or more, which is a much stronger manipulation than a late night or two. The consolidation account explains why sleep may matter, but it is a model, and it does not show that any product, sound or technique strengthens memory during sleep.

Sleep-duration recommendations are expert consensus about health in general, not personal targets, and sleep needs differ between people [7]. This article is general science education and is not medical advice.

Frequently asked questions

Should I stay up to study, or go to bed? A sleepless night has costs for attention and for taking in new material [3][2], and people short of sleep may not notice how much their performance has dropped [6]. For most students, reviewing earlier and then sleeping is the safer plan, although no study can tell you what is best for one particular exam.

Can a nap make up for lost sleep? In the 2021 meta-analysis, the memory benefit was smaller after daytime naps than after natural night-time sleep [1]. The evidence does not support treating a nap as a substitute for a full night.

References

  1. Berres, S., & Erdfelder, E. (2021). The sleep benefit in episodic memory: An integrative review and a meta-analysis. Psychological Bulletin, 147(12), 1309–1353. https://doi.org/10.1037/bul0000350
  2. Newbury, C. R., Crowley, R., Rastle, K., & Tamminen, J. (2021). Sleep deprivation and memory: Meta-analytic reviews of studies on sleep deprivation before and after learning. Psychological Bulletin, 147(11), 1215–1240. https://doi.org/10.1037/bul0000348
  3. Lim, J., & Dinges, D. F. (2010). A meta-analysis of the impact of short-term sleep deprivation on cognitive variables. Psychological Bulletin, 136(3), 375–389. https://doi.org/10.1037/a0018883
  4. Rasch, B., & Born, J. (2013). About Sleep's Role in Memory. Physiological Reviews, 93(2), 681–766. https://doi.org/10.1152/physrev.00032.2012
  5. Lowe, C. J., Safati, A., & Hall, P. A. (2017). The neurocognitive consequences of sleep restriction: A meta-analytic review. Neuroscience & Biobehavioral Reviews, 80, 586–604. https://doi.org/10.1016/j.neubiorev.2017.07.010
  6. Van Dongen, H. P. A., Maislin, G., Mullington, J. M., & Dinges, D. F. (2003). The Cumulative Cost of Additional Wakefulness: Dose-Response Effects on Neurobehavioral Functions and Sleep Physiology From Chronic Sleep Restriction and Total Sleep Deprivation. Sleep, 26(2), 117–126. https://doi.org/10.1093/sleep/26.2.117
  7. Watson, N. F., Badr, M. S., Belenky, G., Bliwise, D. L., Buxton, O. M., Buysse, D., et al. (2015). Recommended Amount of Sleep for a Healthy Adult: A Joint Consensus Statement of the American Academy of Sleep Medicine and Sleep Research Society. Sleep. https://doi.org/10.5665/sleep.4716
  8. Paruthi, S., Brooks, L. J., D’Ambrosio, C., Hall, W. A., Kotagal, S., Lloyd, R. M., et al. (2016). Recommended Amount of Sleep for Pediatric Populations: A Consensus Statement of the American Academy of Sleep Medicine. Journal of Clinical Sleep Medicine, 12(6), 785–786. https://doi.org/10.5664/jcsm.5866
  9. Irish, L. A., Kline, C. E., Gunn, H. E., Buysse, D. J., & Hall, M. H. (2015). The role of sleep hygiene in promoting public health: A review of empirical evidence. Sleep Medicine Reviews, 22, 23–36. https://doi.org/10.1016/j.smrv.2014.10.001
  10. Levinson, D. B., Stoll, E. L., Kindy, S. D., Merry, H. L., & Davidson, R. J. (2014). A mind you can count on: Validating breath counting as a behavioral measure of mindfulness. Frontiers in Psychology, 5, 1202. https://doi.org/10.3389/fpsyg.2014.01202