Does REM sleep really play a role in improving memory?

We’ve explored the effects of REM sleep on memory and discussed that while both animal and human studies suggest that it plays a role, factors such as stress can also have a significant impact.

 

Sleep is one of the basic human needs for survival. According to the dictionary, sleep is “a state in which the eyes are closed and conscious activity is at rest.” We spend a third of our lives sleeping, so we spend a lot of time sleeping, but nowadays, with our busy lives, sleep is often considered a luxury. Workers often get home from work late, forcing them to sleep late, and students often cut back on sleep due to endless homework and test prep, often sleeping far less than they need to be healthy. For many people, this amount of sleep is unrealistic. Many people have gotten used to living on less sleep because they feel they can get by without it. However, sleep is necessary for many reasons, including rest, recharging energy from daytime activities, immunity, and concentration. One of them is to improve memory. While scientists are still debating the relationship between sleep and memory, many believe that REM (Rapid Eye Movement) sleep, a phase of the sleep cycle, is important for improving memory. However, because reaching REM sleep doesn’t necessarily mean you remember everything you’ve recently learned, it’s difficult to claim that REM sleep helps memory in all situations and conditions. Therefore, to examine this claim, we need to understand how REM sleep affects memory.
When we close our eyes and fall asleep, our sleep cycle begins. There are about five stages of the sleep cycle, and different things happen in the body and brain during each stage. The first stage happens when you’re just falling asleep. Neural activity becomes asynchronous, and wakefulness occurs. At the same time, the brain produces a lot of theta waves, which are the brain waves that are usually associated with drowsiness. In the next stage, the pulse and breathing slow down, brain waves become longer and slower, and sleep spindles (brain waves with low amplitude and a frequency of 12 to 14 Hz) begin. In the third stage, as deep sleep begins, breathing, heartbeat, and all brain activity slow down even more, and neural activity synchronizes. The brain then forms large, slow delta waves. Unlike theta waves, delta waves are the brain waves that appear when you’re almost motionless and deeply asleep. In the fourth stage, your pulse, breathing, and brain activity slow down the most. Brain waves are highly synchronized, nerve cell activity is lower overall, and the amount of slow delta waves increases. The fifth stage of the sleep cycle is when you reach REM sleep, which is known to be the most conducive to memory. In this stage, the eyeballs move back and forth quickly, and dreams become more vivid and frequent. Muscles are relaxed, and a process occurs in the brain that allows you to store many of the things you learned and studied during the day for long term memory.
Many scientists emphasize the importance of REM sleep. There are studies and data that suggest that REM sleep is a factor that contributes to memory when you sleep. These results have been obtained through animal experiments and show how important REM sleep is for memory. For example, rats were used to learn to navigate a complex maze with food at the end of the maze, and when the rats learned to navigate the maze to the food, the amount of REM sleep increased. The researchers suggest that the increased REM sleep required to learn new knowledge suggests that REM sleep is important in the process of memorizing and cementing new facts in the brain. However, these changes in REM sleep may not be due to a link between memory and REM sleep. The fact that REM sleep increased in a condition where rats likely learned less over several repeated trials suggests that there are other factors driving the increase. REM sleep may have been triggered by the pressure, stress, and emotional stimulation of being trapped in a maze, unable to find food, and forced to find the end of the maze. In fact, one study showed that REM sleep increased when animals were subjected to the right amount of stress. So stress, emotional factors, and learning are hard to measure and separate, and it’s hard to say for sure what affects REM sleep.
Other animal studies have used specific mice to study how memory is affected by significantly reducing REM sleep. The hypothesis was that if they were able to remember and learn new things with almost no REM sleep, it would be evidence that REM sleep doesn’t contribute much to memory. In practice, many scientists have observed rats on a platform floating on water. They use the “platform technique,” in which the rats’ leg muscles relax as they approach the REM sleep stage, causing them to fall into the water and not be able to wake up and fall back into REM sleep. These rats had a harder time learning new tasks than normal rats, showing a significant decrease in learning ability. It has been argued that this is due to the fact that during REM sleep, knowledge is cemented and memorized, requiring the steps necessary to complete a new task. However, this phenomenon may not be caused by REM sleep. When active animals like rats are placed on a platform and their movements are controlled, it can be very stressful. Falling into cold water can also cause symptoms of hypothermia, which can also increase stress. Many studies have already shown that acute stress can cause the release of the hormone cortisol, which can dramatically impair memory. When rats injected with the hormone cortisol were asked to learn the path of a maze, fewer rats were able to reach the end, they made more mistakes, and it took them much longer than normal rats. So even in this case, it’s likely that stress was more damaging to memory than REM sleep.
Comparing REM sleep between rats and humans is not appropriate because animal studies have limitations, there is no certainty that they can be applied to humans, and the amount of REM sleep varies between animals. Therefore, it is important to review the results of human studies that show a relationship between REM sleep and memory. Similar to animal studies, it was studied whether the amount of REM sleep increased when people were given tasks that required them to remember new information. Smith and Lapp’s study found that when students’ sleep cycles were monitored after the test period, the duration of REM sleep did not increase, but the density did. These results refute the idea that stress increases the amount of REM sleep and suggest that REM sleep may be important for the memorization required to study for exams. However, the control group in this experiment was students who did not take the test due to personal circumstances. The results may be unreliable because it was not possible to prove that there was a significant difference in the amount of new material learned and memorized by these students compared to those who took the test, and it was not possible to ensure that factors such as stress, which can disrupt sleep, were constant across all students. So how would eliminating REM sleep in humans, as it has been done in animals, affect memory? In theory, lesions in the brain stem due to disease or injury would eliminate REM sleep. However, research shows no clear evidence or reports that people without this part of the brain have a reduced or lost ability to make new memories. This contradicts the claim that REM sleep helps form and consolidate memories and could be used as evidence that there is no relationship between the two.
In everyday life, many high school and college students often have to pull all-nighters to study for exams. This results in little or no REM sleep and disrupted sleep. In my personal experience, I’ve often found that when I’ve studied something over and over again in my head, I’ve been able to recall the material slowly without going through the REM sleep stage because I didn’t sleep, and I’ve eventually remembered it all and done well on the test. In other words, it’s possible that your poor memory is a result of factors such as lack of focus or stress. Also, genetically, the amount of sleep or REM sleep needed varies from person to person, and it also depends on the upbringing of the individual. Some students may be sleep-deprived for years, which raises the question of whether the brain may become accustomed to this condition due to repetition, and whether memory is less affected in people who are accustomed to sleep deprivation compared to those who have always had REM sleep. If this phenomenon exists, more research needs to be done to see if it is reversed by prolonged exposure to REM sleep.
Sleep is very important for humans for many reasons, and memory is one of them. It is widely recognized that we need enough sleep to have the best memory, and there are many reasons for this phenomenon. While many scientists emphasize the importance of REM sleep, it’s still under debate, so it’s not always easy to accept REM sleep as an important factor in memory based on current research. There is also a lot of contradictory evidence that suggests REM sleep is not as important as some scientists claim, so the significance of its effect on memory is unclear and needs more research and study.