The Relationship Between Sleep and Memory

Without a full night’s sleep, memory consolidation and learning abilities suffer. Understanding how memory and sleep are linked can help us realize the importance of sleep.

By Nicole Gleichmann

Jan 6th, 2021

Have you ever noticed that when you don’t get enough sleep, your memory suffers? Maybe you forget where you put your keys, you space out on an important meeting, or you don’t do so well on an exam. These instances all point to the important role that sleep plays in our memory.

And with many of us not spending enough hours snuggled under the blankets each night (I can’t be the only one who has gotten carried away on a new Netflix series…), understanding exactly how sleep can impact our memories might be just what we need to prioritize sleep a bit more.

In this article, we’re going to share with you what memory is and how sleep can support it. We will help you understand how sleep deprivation affects memory, and why you should do your best to get enough sleep each night.

What is Memory?

Memory is defined as “the process of taking in information from the world around us, processing it, storing it, and later recalling that information.” From this definition, it’s easy to understand the three phases of memory: acquisition, consolation, and recall.

During memory acquisition, a trace of a fact or experience is saved as short-term memory in your brain. In this early stage, it’s easy for a memory to slowly degrade or be changed or influence. In the consolidation stage, the memory is moved from short-term memory to long-term memory. Once a memory is stored in long-term memory, you are capable of recalling this memory, which is the final stage of memory.

There are many types of memory, some obvious and others less so. For example, the first type of memory that generally comes to mind is learning facts, language, or recalling events. There are other, less obvious types of memory, such as recognizing faces of those you know, or your immune system remembering an antigen that it conquered that day.

Memory formation and recall is a product of something known as neuroplasticity or brain plasticity, which is the ability of your brain to adapt and change due to activities or experiences.  What this means is that when you see something, do something, or learn something, changes occur in the physiology of your brain, resulting in memories.

Understanding Memories

You know how there are certain experiences in your life that you remember forever? But others that you forget nearly as quickly as they happen? This demonstrates that memories don’t just happen immediately and stay forever, but instead that memory is selective and gradual.

Memories are often imperfect as well. This is best exemplified by the times when you and a friend, family member, or coworker have a conversation, but both remember it differently. One of you…and possibly both of you…aren’t remembering the conversation exactly as it happened. This is also why witnesses of crimes have often accused the wrong person of committing a crime; they think they remember who they saw doing something, but in fact, their memory doesn’t match up with historical facts.

How Memories Form

When you learn or experience something (memory acquisition), neural activity spikes in your brain, beginning to form connections between neurons (brain cells). This cluster of activity is the initial formation of a memory, and in this early state, is stored in what we call short-term memory, meaning that the memory is in a holding state. For example, humans can remember 10 numbers told to them directly after they hear them, but check back in a few hours, and most people won’t remember any of these numbers.

In order for memories to move from short-term memory to long-term memory, consolidation must occur. This happens when the connection between neurons is strengthened, forming synapses in the brain (synapses connect neurons). Some short-term memories are moved to long-term memory through consolidation, while others are weakened and lost.

So, why are some memories consolidated and others pruned? While scientists are still at work trying to fully understand this process, we do know some things about memory consolidation.

The primary idea is this: the more often a specific synapse (or group of synapses) is strengthened – say by practicing a new language or replaying an emotional experience in your mind – the stronger this connection becomes, helping to solidify this memory. However, if you learn a new word in Spanish and never practice it, or if you have a conversation that doesn’t mean much to you and you don’t think about it later, that neural activity is going to weaken, leading to your forgetting the word or the conversation.

But this is just part of the story; it’s not just practicing something or replaying a memory in your mind that can lead to the strengthening of synapses and thus long-term memory formation. Another player in the accuracy and longevity of your memories is sleep.

Sleep and Memory

When you were in school, your parents or teachers probably told you to get your rest because getting a good night’s sleep will help you to be sharper the following day. And they were right; while your body rests, your brain is active in such a way as to impact your memory and learning abilities.

As you cycle through different stages of sleep, your brain undergoes processes that prune some memories and consolidate or strengthen others. In particular, sleep appears to play a key role in moving memories from short-term memory to long-term memory, which is the definition of memory consolidation.

There are two types of memory for which sleep is believed to play a central role:

  1. Declarative Memory: Knowledge of fact-based information, such as what you did yesterday or how to say “goodbye” in a foreign language.
  2. Procedural Memory: Knowledge about how something is done, such as riding a bicycle or playing the piano.

Sleep Stages and Memory Consolidation

Every night when we sleep, our brain cycles through varying levels of activity that are known as sleep stages:

  1. Stage 1 Sleep: You can think of this first stage of sleep as your body and brain slowly transitioning from waking to sleeping. Considered light sleep, it’s easy to be woken up during this stage of sleep.
  2. Stage 2 Sleep: During stage 2 sleep, it’s still fairly easy to be woken up, so it too is considered a stage of light sleep. Your body temperature and brain waves continue to slow.
  3. Stage 3 Sleep: Also known as deep sleep or slow wave sleep, this stage of sleep is believed to play a central role in rejuvenation. How rested you feel when you wake up is correlated with how much deep sleep you achieve.
  4. REM (Rapid Eye Movement) Sleep: REM sleep is one of the most well-known stages of sleep because it’s when you dream. Your brain activity is similar to that of when you’re awake, with faster brain waves that during deep sleep.

We have long known that REM sleep, during which we dream, plays a function in consolidating memories. Recently we’ve learned that deep sleep, too, plays a central role in memory consolidation. Exactly how sleep and declarative memory are linked is still being investigated.

As for procedural memory, scientists have found that light sleep, deep sleep, and REM sleep are all involved. For instance, light sleep in linked to motor learning (think riding a bike), deep sleep and REM sleep to visual learning (recognizing the face of someone you just met), and REM sleep to procedural memory consolidation.

Your Brain During Sleep

While you sleep, regions of your brain central to memory are active, including your hippocampus, amygdala, and neocortex.

Short-term memories are primarily stored in your hippocampus. During deep, stage 3 sleep, some of these memories are transferred to your neocortex, where long-term memories are stored. This transfer can also occur during other non-REM sleep stages and when you’re awake.

During REM sleep, your neocortex is at work replaying these memories through repetition while you dream. When we learn a lot of facts during the day, it seems that we spend more time in REM sleep. This suggests that REM sleep plays some role in learning, even if the role is allowing the brain to rest so that it can perform well at learning the following day.

Sleep Is Critical for Performance and Learning New Information

While much of the attention on sleep and memory is centered around memory consolidation, this is not the only role that sleep plays in memory. When we don’t sleep enough, or when we don’t sleep soundly, our learning abilities are also impaired. This means that you’re more likely to remember what you learn on days when you’ve had 8 hours of sleep the night before than on days when you only slept for four hours or tossed and turned the whole night.

One reason why insufficient nightly sleep hinders learning abilities is that it lessens our ability to focus. Additionally, sleep is important for rejuvenation, and when we don’t get enough, we might find that we have a lack of energy or desire to learn new things.

Researchers have even found that inadequate sleep can lead to an increased chance of our getting sick. One possible reason for this could be that our immune systems don’t properly remember the antigens that they encountered the previous day, allowing an antigen to multiply, leading to a cold or other illness.

Furthermore, when we don’t get enough sleep, we don’t give our neurons time to rest and recover. Without sleep, our neurons don’t work as well, and even the ability to create short-term memories suffers.

Final Thoughts

Healthy sleep plays a central role in our ability to learn and consolidate memories. In order to perform at your best, it’s crucial for you to clock 7 or more hours of sleep nightly. Not doing so can lead to inhibited memory processes, not to mention decreased emotional and physical health. If you want to improve your memory, the first step is improving your sleep hygiene. If you don’t get enough sleep one night, try to fit in a 30-minute nap to support memory and cognitive rejuvenation.