Poor Sleep = Poor Learning

Dr Piotr Wozniak, Fall 2007

This article contains a few hints on how sleep affects learning


Sleep and learning

Why is sleep important?

If I was to bet on the top two factors that hinder learning in industrialized nations, these would be (1) stress and (2) poor sleep:

  1. Stress takes away your focus, stifles creativity, and can contribute to poor sleep
  2. Sleep is needed for consolidating and optimizing memories. Without sleep, you cannot even experience the sense of a "good day"

Health is important too, but, statistically, it is stress and bad sleep that affect nearly everyone, and take the largest toll. Reduce stress and improve sleep, and you might see a society changed beyond recognition!

For healthy people, all other factors in learning seem to be somewhat secondary. Self-discipline improves greatly if you are rested and happy. The fun of learning follows. The way you approach learning, tools and techniques, the way you represent knowledge in your mind, they can all be improved gradually and consistently. If you are on a steady path ahead, success is nearly guaranteed. Metaphorically speaking, your brain comes with a solid warranty of progress that you can easily void with stress and/or poor sleep.

Given the importance of sleep, unless you are a "natural" and never get a bad night sleep, you should understand the basics of sleep physiology and the impact of your sleep habits on learning. Moreover, even if you sleep well today, you are always in danger of ruining your sleep patterns through the use of computers, Internet, mobile phones, SuperMemo, etc. In short, the human brain has not yet got enough time to evolve and adapt to the stimuli of the modern lifestyle. That's why we witness an epidemic of sleep disorders in industrialized nations.

Sleep and Learning Research

Everyone knows that without a good night in bed, the next day can be ruined. When sleepy, you can easily shovel the garden in fresh air, but if you try some creative work in front of your computer in a warm room, your brain will tend to switch off and stifle any creative progress. 

It is quite evident that mental functions and learning are the primary victims of sleep deprivation. Scientists have for long suspected that the main function of sleep is related to learning and memory. Even in 17th century, John Locke campaigned for good sleep for kids for those reasons. However, only recent decades and years brought an exponential increase in evidence demonstrating the role of sleep in memory. There are still prominent sleep researchers that dispute the link. Some insist that only a conscious brain can be involved in memory. Others claim that sleep is like eating, if you can get more, you will always want to. Outside scientific community, sleep is held in amazing disregard. Many people do not want to waste time on sleep to economize more time for work and "creativity". Others try to get "best" sleep in minimum time (see polyphasic sleep).

The worst part of that disregard is that little kids worldwide are woken up early in the morning to go to school to "learn". Not only does their learning suffer, or even becomes futile; not only do those kids get stressed and cranky; their health can be affected. Their immune systems undermined. Their long-term development stunted. Some sleep researchers try to battle the establishment for more rational school schedules (hats off to Dr Mary Carskadon; interview). At the same time, the ever-present rat race produces forces in the US, in Europe, and beyond, that insist on even earlier school hours. That comes from both parents and from the authorities. They all bring up a spurious and biologically untenable excuse: the kids can just go to sleep earlier.

In this gloom and doom scenario, there is still a ray of hope though. Science is slow to percolate into social awareness; however, in the end, it wins most of the time (except where it needs to combat stronger forces; e.g. intelligent design theories will keep strong with the backing of religion). My optimistic prediction is that, sooner or later, governments, school authorities, and parents, will realize that the use of an alarm clock contradicts the goals of education that makes them rip their kids from their beds in the first place!

How SuperMemo and SleepChart can contribute to sleep research?

Having been involved in the subject of memory and learning for 20 years now, I have spotted an opportunity to produce some solid evidence that could contribute to the cause of demonstrating the importance of sleep in learning. One of beautiful things about SuperMemo, is that it keeps a detailed record of memory performance while you learn. If that record could be combined with measurements of sleep quality before and after learning, an ocean of research opportunities would emerge. In 2003, SleepChart freeware was released. That application provided the missing link. With SuperMemo and SleepChart, we can collect data that can provide answers to a virtually infinite set of questions about sleep and learning.

My first, most atavistic, and raw intuition was that it should be easy to show that short sleep produces poor learning. I took my own sleep-and-learning data to quickly investigate such a correlation. However, nearly a reverse relationship could be demonstrated. In retrospect, the paradox is very easy to explain: in free running sleep (which I practise religiously), there is a correlation between the quality of sleep and its length: the better the alignment of the sleep block with the circadian rhythm, the shorter the sleep, and the better its quality. It became apparent that little evidence can be garnered without considering the circadian timing of learning (i.e. the time of learning in reference to the waking hour). Sadly, earlier versions of SuperMemo kept only the date of the repetition, not its precise time. That has changed with SuperMemo 2006 released a few months ago. Now it is possible to correlate sleep data with learning in precise time frames!

First Conclusions

Over the last few months, I tried to see what conclusions could be drawn from the newly available data, which I collected from a few early adopters of SuperMemo 2006. The data is scarce, the period was short, however, the potential value of correlative investigations can already be seen. Here are a few cursory glimpses at the data:

Recall: This is an exemplary graph that demonstrates a decline in recall throughout a waking day:

As the day goes on, our ability to recall facts from memory is getting worse and worse. Interestingly, even a short nap seems to bring back the recall to the baseline level. In other words, there seems to be a direct link between recall and alertness. Recall seems to be reversely correlated with the homeostatic drive to sleep. A slight increase in recall around the 12th hour of wakefulness is a reflection of the circadian component of alertness. The waviness at later waking hours seen in the graph comes from scarcity of data as learning at later hours makes little sense (of total 31,000 repetitions used to plot the graph, only 684 fell beyond the 10th hour of waking).

Consolidation: Nearly identical relationships holds true for memory consolidation:

As the day goes on, your ability to store facts in memory declines. The graph has been constructed by correlating the time of learning (in reference to waking time), and the grade scored in the next repetition (often months after the original learning). Again, naps seem to restore the consolidation power to baseline. As much as recall, consolidation seems to be reversely correlated with the homeostatic drive to sleep. A slight increase in the quality of learning can also be seen around the 12th hour of natural waking.

The conclusion, which you have probably observed yourself (assuming you do not use an alarm clock), is that in free running sleep, we can get best learning results if we learn early in the morning shortly after awakening. The same holds for exams. You can show best recall if your exam is held in the morning (assuming you do not need the alarm clock to wake up for the exam). Good sleep is needed as much before learning (for the sake of recall), as it is needed after learning (for the sake of consolidation).

Alarm clock: There is an urgent need to collect sleep data from subjects who disrespect healthy sleep in various ways. The most interesting area for further investigation is how poor sleep hygiene affects learning. As an example, let's have a peek at an interesting graph showing the average recall of a teenager who often needs to get up early for school, far ahead of his natural waking time. If grades are converted to the forgetting index, we can see that this students forgets 53% more on schooldays when he needs to get up early. This is a very preliminary sample that should not be used to draw far-reaching conclusion (for example, more learning occurred in earlier hours on days free from school), however, it is my hope that with more data pouring in, we can tangibly demonstrate the disastrous impact of alarm clocks on learning:

In other data sets, it has also be found that later waking up (after 11 am) often correlates with lower grades again (perhaps as a result of weekend late "partying" that results in poorer sleep and later awakening).

Daily alertness cycle: For a busy father of two kids with little chance to catch a nap, the homeostatic decline in grades throughout the day is superimposed on the circadian components of sleepiness with a substantial dip at 12:00-14:00 o'clock. Good morning performance is amplified in the morning by a cup of coffee. At the same time, a habit of drinking beer in the evening finds also its reflection in lowest grades after midnight. 

Free running sleep: The above graph should not be used as an absolute guideline for optimum learning. Everyone will have his own optimum hours that depend on one's circadian rhythm. For most people, optimum learning occurs in the morning and after a siesta. Non-nappers also improve their learning in the evening due to a circadian upswing. However, the exact timing of those optimum periods can only be determined on an individual basis. The disconnect between the optimum learning time and the absolute clock can be seen in a regular free running sleep rhythm as in the analogous graph below that does not show any hours in which learning is more efficient:

However, when the free-running sleep data presented in the graph above is processed using the circadian phase rather than the clock phase, a typical two-peak circadian pattern re-emerges with good grades in the morning, siesta dip, and an evening upswing. The circadian phase estimations have been generated with SleepChart. The peak learning times are usually separated by 10-13 hours:

Learning overload: The more time you spend learning on a given day, the lower your learning capacity. Recall decreases along a homeostatic increase in sleepiness. However, it decreases much faster if you continue learning. That observation agrees nicely with complementary encoding theories that explain how the brain copes with catastrophic forgetting that occurs in artificial neural networks. Those theories speak of secondary memory systems used to redistribute knowledge stored with low-interference short-term networks. The act of storage redistribution is hypothesized to occur during sleep. In other words, as you keep loading your memory with knowledge, your brain turns on a defense mechanism, makes you drowsy and sends you to an earlier sleep. This is why, against conventional advise of sleep experts, I recommend SuperMemo to insomniacs. Except where the circadian component of sleepiness is missing, learning is a good tool for boosting homeostatic sleepiness (except in cases like learning before an exam, which may subconsciously be associated with stress).

Alertness multiplier: It is obvious that alertness improves learning. However, it is worth noting that even marginal improvements to high alertness can yield major benefits to learning. Once you are sleepy, your learning results are poor. However, it is not enough to be alert. Crisp alertness might substantially improve learning as compared with just being ok. In the graph below, sleep propensity has been estimated with SleepChart:


Submit your data

Invitation to submit your data

As I tried to show above, many interesting conclusions can be drawn when analyzing sleep and learning data. What we need now is a more comprehensive analysis of larger datasets from individuals with disparate lifestyles, sleep and learning habits.

If you use SuperMemo 2006 and have your sleep data collected with SleepChart, please submit your learning data as suggested below. The more you learn, the more valuable the data is. The more unusual your lifestyle, the greater the chance your data could uncover precious truths. 

If you keep your sleep data in another format, it could be equally valuable. If you use older SuperMemos, your data could still be used to draw conclusions.

Your contribution will be particularly precious if you are on any kind of a crazy sleep schedule: short sleep, irregular schedule, shift work, polyphasic experiment, etc. The messier your sleep, the greater its research value. In addition to the research value of your data, if I manage to generate an individual assessment for you, you can boost your understanding of your own sleep and learning.  

If you do not have any sleep data (only your SuperMemo learning results), your data can still make a contribution, especially, if your sleeping habits are very regular and well defined (as in the graph of daily alertness cycle above). 

How to submit

Send your (1) sleep.tim, (2) <collection>.kno and (3) RepetitionHist.dat files via e-mail. For detail see: How to submit your sleep and learning data.


If this research program is as successful as I predict, it should affect future versions of SuperMemo. You may know, there is a substantial opposition against making SuperMemo yet more complex. Therefore, I will need to demonstrate black-on-white how important sleep data is for optimizing the learning process. Integrating those basic self-research tools with SuperMemo will help push the learning efficiency to a new level, esp. in people who experience problems with sleep.


Although the conclusions drawn above are preliminary, and the correlations shown not always exactly prove the points below, sleep research literature makes the following tenets look solid: