Sleep and the Brain: Memory, Creativity and Problem Solving
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A few weeks ago we discussed the importance of sleep for removing waste. During sleep, cerebrospinal fluid helps to pick up all of the waste products that have accumulated in your brain throughout the course of the day. This cerebrospinal fluid wash is crucial for repairing damage, preparing the brain for the next day, and disposing of harmful products, including β-amyloid, which is associated with Alzheimer’s disease. We’ve also discussed the importance of sleep for regulating appetite, recovering from a hard workout, and restoring energy levels. When you sleep well, you just feel awesome!
This week we’re going to dive into sleep's effect on mental performance. I’m sure you’ve noticed on days you don't get a good sleep, you struggle to concentrate, are unable to recall facts, and find it difficult to solve problems. It’s also well established that students’ academic performance is correlated with sleep quantity and quality.
But what exactly is happening at night that helps us think clearly the next day?
Our brain is made up of around 100 billion neurons, or nerve cells. When we sleep, new connections are made between these neurons. These connections are critical because they allow us to create memories, learn a new skill, think creatively, and problem solve. What’s more, scientists are now learning that the different stages of sleep have very different and important roles when it comes to mental performance.
As discussed in previous newsletters, we cycle through two main sleep stages throughout the night: rapid eye movement (REM) sleep, and non-rapid eye movement (NREM) sleep. NREM sleep is then further divided into stages 1, 2, 3, and 4. Stages 1 and 2 are considered light sleep, and stages 3 and 4 are deep sleep. Deep sleep occurs more at the beginning of the night, whereas REM sleep occurs more at the end of the night.
So what do these sleep stages have to do with mental performance?
There are three main steps to memory formation: Encoding, Consolidation, and Recall. Encoding is the process in which we take up new information. Consolidation is taking that information and moving it from one part of the brain to another, from short-term to long-term storage. Recall is then calling upon this information when we need it. While encoding and recall occur when we’re awake, deep sleep is particularly important for memory consolidation. This is similar to how deep sleep is essential for our immune system to fight off pathogens and can even help the effectiveness of certain vaccines (so if you’re getting your COVID-19 vaccine, make sure you get a good night’s sleep after!).
While NREM sleep is important for memory, research has shown that REM sleep is important for problem solving and creativity. This is because during REM sleep, your brain replays this newly-stored information and compares it with other stored memories - making new connections and associations, and seeing problems in a different way. If you’ve ever woken up to a “Eureka!” moment, you probably were just in REM sleep!
So in order to learn, create, problem solve, and perform at your best the next day, you need to make sure you’re getting 5 complete sleep cycles (about 7.5 hours) to get the proper amount of deep and REM sleep.
Happy sleeping!
What are we finding in the research?
Last year a team of researchers proposed that both NREM and REM sleep are important for creative problem-solving in different but complementary ways. They suggest that during NREM, information is transferred from the hippocampus to the cortex (from short to long term storage). Then during REM, this information is compared with already stored pieces of information to make new connections and associations. The researchers hypothesize that both sleep states are important for creative problem-solving to take place.
Hypothetical model from Lewis et al. 2020. During NREM sleep, new information (grey circles) is moved from the hippocampus to the neocortex (green circles). During REM sleep, connections are made between this newly stored information and previously stored information (purple circles) to make new connections (blue circles). Each time this process is repeated, more connections and associations are made.
