In this blog post, we will take a closer look at the importance of REM sleep on memory through various scientific studies and examples.
Sleep is one of the basic needs for human survival. According to the Korean dictionary, sleep is “a state of rest in which the eyes are closed and the consciousness is dormant.” People spend a lot of time sleeping, as they spend a third of their lives sleeping, but nowadays, people often consider sleep a luxury as they lead busy lives. For office workers, when they come home from work late, they have no choice but to sleep late, and students often reduce their sleep time due to endless homework and test preparation, so they often sleep much less than they need for their health. For many people, such sleep time is not realistic. They are often accustomed to living with less sleep because they can get by with less sleep. But sleep is necessary for many reasons, including rest, recharging the energy expended during the day, and improving immunity and concentration. One of the benefits of sleep is improved memory. Scientists are still debating the relationship between sleep and memory, but many scientists believe that REM (rapid eye movement) sleep, a stage of the sleep cycle, is important for improving memory. However, it is difficult to claim that REM sleep helps memory in all situations and conditions, because reaching REM sleep does not necessarily mean that you will remember everything you have learned recently. Therefore, to examine this claim, it is necessary to find out how REM sleep affects memory.
When we close our eyes and fall asleep, the sleep cycle begins. There are about five stages in the sleep cycle, and various phenomena occur in our body and brain at each stage. The first stage occurs when people just fall asleep. Neural activity becomes asynchronous, and the sense of sleepiness arises. At the same time, theta waves, which are mainly brain waves that appear when sleepiness occurs, are formed in the brain. In the next stage, the pulse and breathing slow down, and the brain waves become longer and slower. Also, the sleep spindle (brain waves with low amplitude and a frequency of 12-14 Hz) begins. In the third stage, as deep sleep begins, breathing, heartbeat, and all brain activity slow down and neural activity becomes synchronized. Then, the brain forms large, slow delta waves. Unlike the theta waves, delta waves are barely noticeable and are the brain waves that appear when you are in a deep sleep. In the fourth stage, the pulse, breathing, and brain activity slow down the most. The brain waves are largely synchronized, and the activity of nerve cells is low overall. The amount of slow delta waves also increases. The fifth stage of the sleep cycle is the stage where you reach REM sleep, which is known to be the most beneficial for memory. In this stage, the eyeballs move back and forth quickly, and dreams become more vivid and frequent. Muscle tension is released, and the brain stores a lot of what you have learned and studied during the day so that it can be remembered for a long time.
Many scientists emphasize the importance of REM sleep. This is because there are studies and data suggesting that REM sleep is a factor that helps memory when sleeping. These results were obtained through animal experiments and showed how important REM sleep is for memory. For example, mice were used to study how mice learn to reach the location of food at the end of a maze by following a complex path, and the results showed that the amount of REM sleep increased. The researchers argue that the increased REM sleep in learning new knowledge is important for the process of memorizing new facts and consolidating that knowledge in the brain. However, this change in REM sleep may not be due to the association between memory and REM sleep. The fact that REM sleep increased in the presence of conditions that might have reduced the amount of learning in the mice in several repeated experiments indicates that there are other factors that cause the increase. REM sleep may have occurred because the mice were trapped in a maze and forced to find the end of the maze under pressure, stress, and emotional stimulation. In fact, one study found that when animals are under an appropriate amount of stress, REM sleep increases. Therefore, stress, emotional factors, and learning are difficult to measure and separate, and it is difficult to determine with certainty what affects REM sleep.
Other animal experiments have used specific mice to study how much REM sleep affects memory by significantly reducing it. This is based on the hypothesis that if something is learned or remembered while REM sleep is almost absent, it is evidence that REM sleep is not a significant factor in memory. In fact, many scientists put the mice on a platform floating on the water and observed them. They used the “platform technique,” in which the mice’s leg muscles relax when they reach the REM sleep stage, causing them to fall into the water and wake up, preventing them from falling back into REM sleep. These rats had a significantly lower learning capacity than normal rats when learning new tasks. This was argued to be because the process of consolidating and memorizing the knowledge required to complete new tasks occurs as they reach the REM sleep stage. However, this phenomenon may not be caused by REM sleep. Animals that are active like mice can become severely stressed if they are placed on a platform and their movements are controlled. They may also develop symptoms of hypothermia due to falling into cold water, which can also increase stress. Many studies have already shown that acute stress can cause a sharp decline in memory by secreting the hormone cortisol. When compared to normal rats, fewer rats that had been injected with cortisol hormone were able to learn the path of the maze, and they made more mistakes and took much longer to complete the task. Therefore, even in this case, it is highly likely that stress caused more damage to memory than REM sleep.
Animal experiments have limitations, there is no certainty as to whether they can be applied to humans, and the amount of REM sleep varies among animals, so it is not appropriate to compare REM sleep in rats with that in humans. Therefore, it is necessary to review the research results showing the relationship between REM sleep and memory through human experiments. As with animal experiments, it was studied whether the amount of REM sleep increases when people are given tasks that require them to remember new information. Smith and Lapp’s study found that after the exam period, the students’ sleep cycles were observed, and although the time of REM sleep did not increase, the density did. These results refute the claim that stress increases the amount of REM sleep and show that REM sleep may be important for memorization necessary for studying for exams. However, the control group used in this experiment was made up of students who did not take the test due to personal circumstances. The results may be less reliable because it was not possible to prove that there was a significant difference in the amount of new learning and memorization between these students and the students who took the test, and it was not possible to confirm that factors such as stress that can interfere with sleep were consistent among all students. So, what effect would it have on memory if REM sleep were eliminated in humans, as it was in animals in the experiment? In theory, if a lesion occurs in the brain stem due to illness or injury, it is the same as if REM sleep were eliminated. However, research has not found clear evidence or reports that people without these parts of the brain have a reduced or absent ability to create new memories. This is inconsistent with the claim that REM sleep helps to form and consolidate memories and may be used as evidence that the two are unrelated.
In everyday life, many middle and high school and college students often have to study for several nights in a row for exams. When this happens, people either don’t get any REM sleep or their REM sleep is interrupted. In my personal experience, if I keep thinking about the content I’ve studied over and over in my head, I sometimes end up remembering the content slowly without going through the REM sleep stage, and I end up remembering everything and doing well on the test. In other words, if a person’s memory is poor because they don’t sleep, it is not impossible that this is the result of factors such as a lack of concentration or stress. Also, the amount of sleep and REM sleep that each person needs may differ genetically, and may also differ depending on the environment in which they grew up. Some students may have been sleep-deprived for several years, and it is possible that this repetition may cause the brain to become accustomed to this condition, or that people who are accustomed to sleep deprivation may be less affected by memory loss when they are deprived of REM sleep compared to people who have always had REM sleep. If this phenomenon exists, more research is needed to determine whether prolonged exposure to REM sleep will change this phenomenon.
Sleep is very important for humans for many reasons, and memory is one of them. It is widely known that sufficient sleep is necessary to have the best memory, and there are many reasons for this phenomenon as well. Many scientists emphasize the importance of REM sleep, but since this is still a matter of debate, it may be difficult to unconditionally accept that REM sleep is an important factor that helps memory based on the current research results. In addition, there is a lot of contradictory evidence that REM sleep is not as important as some scientists claim, so the importance of the effect of REM sleep on memory is unclear and more research and study are needed.
