Effects of Sleep on Memory Making

Written By: Naomi Wu

Image from AARP

It is true, your brain is always at work, whether you are making that weekly commute to the grocery store, contemplating life decisions whilst staring at the ceiling, and yes, even when you are asleep. In fact, the vast majority of your mental work, around 90-95% as most scientists estimate, is done unconsciously. You have likely heard the advice to get a good night’s sleep the night before an important event, such as a test, even though it may be tempting to pull an all-nighter. Numerous studies confirm the importance of getting good sleep for maintaining healthy cognitive function, highlighting key connections synthesized by the brain that require enough sleep to emerge in their ideal form. 

To illustrate this concept, Daniel Kahneman, in his work Thinking, Fast and Slow, proposes two different systems by which our brain deals with information: System 1 and System 2. System 1 is responsible for intuitions, hunches, and memory recall. It contains our brain’s Default Mode Network (DMN), which dominates your cognition when you are zoning out during class or work, letting your mind wander, or sleeping. On the other hand, System 2 is slower and more analytical, compensating for intuitive errors in our System 1. System 2, primarily responsible for pointing out logical errors, is the reason why we can compute mental arithmetic and are able to correctly solve a problem. Take the following problem as an example:

A bat and ball cost $1.10

The bat costs 1 dollar more than the ball.

How much does the ball cost?

Without System 2, the intuitive answer would be $0.10. However, if the ball really was $0.10, the bat (which costs 1 dollar more) would be $1.10. Add them together, and you get $1.20, greater than our initial amount. When the default mode network is not backed up by our brain’s analytical functions, it is not sufficient to find the correct answer to the above problem (which is $0.05). 

If your initial answer was $0.10, you were relying on your System 1’s memory recall function, comparing the problem to similar ones you have seen in the past and discerning a possible answer based on that. 

As you can likely imagine, the brain’s default mode network is the same place where memory consolidation occurs; it is at play during the duration in which you are asleep. That is why when one claims to be psychologically inert, the brain is actually doing much more than they believe; they are just unaware of it. 

While you lie unconscious on your bed, your neurons are forming new connections and converting experiences into memories. This is why you may find that letting an idea “marinate” before acting upon it is the ideal approach. The time you spend allowing those thoughts to ruminate in your skull is not “lazy” or “unproductive,” contrary to what commonly held notions may insinuate. Of course though, it is not a good idea either to wait until 11:00pm the night before the deadline to write that essay. 

A study done by the Massachusetts General Hospital underscores the benefits of allocating time to “sleep” on new information, both literally and figuratively. In the study, the subject was instructed to perform a memory task in which he sees a pattern of flashing colored lights, and has to reproduce the sequence in the same order. The researchers measured patterns of neural activity in his brain and recorded them on a computer. At night, the researchers followed him to record activity in his motor cortex as he dozed off to dreamland. The findings revealed a distinctive pattern: from time to time, the subject’s neural firing patterns were congruent with those that occurred when he was playing the game in the daytime, suggesting that he was essentially replaying it in his sleep. Overall, these findings demonstrate the importance of sleep to make sure the brain is able to synthesize such connections.

Another study from the article “A systematic and meta-analytic review of the impact of sleep restriction on memory formation” from Science Direct further confirms the importance of a good night’s rest. In this study, one group of participants undergoes encoding in the daytime hours and is later tested for memory retention, where the other group is allowed a full night’s worth of sleep before being tested. The results indicate that retention intervals that involved sleep significantly outperformed intervals involving wake activities when the test was administered, demonstrating the importance of a restful night for cognitive ability.

Citations:

Crowley et al., Rebecca. “A systematic and meta-analytic review of the impact of sleep restriction on memory formation.” Science Direct, 2024, https://www.sciencedirect.com/science/article/pii/S0149763424003981. Accessed 1 February 2026.

Kahneman, Daniel. Thinking, Fast and Slow. Farrar, Straus and Giroux, 2011.

MGH News and Public Affairs. “Brain practices new tasks while we sleep.” Harvard Gazette, 22 June 2022, https://news.harvard.edu/gazette/story/2022/06/scientists-find-link-between-sleep-and-learning-new-tasks/. Accessed 31 January 2026.