Today a large majority of the population knows or has heard of the concept of REM phase or REM sleep . We know that it forms part of our sleep and that, at least, it presents some differences with regard to the rest of our sleep, non-REM sleep.
Many people do not know what makes this dream so necessary for us. That is why in this article we will make a brief comment on what REM sleep is, and its peculiarities.
The phases of sleep
Sleep is an essential need for human beings and for most living beings. Our organism is a structure that continuously consumes energy, requiring the elements of our “machinery” of rest in order to function properly.
Sleep is essential. However, sleep is not something uniform that comes suddenly. In fact, during sleep there are various cycles composed of different phases, in which different functions are altered and in which our brain reduces or increases certain types of bioelectric activity . Specifically, we usually have between 4 and 9 of these cycles, each of which is divided into five phases. These phases usually follow a certain order.
Firstly, in phase 1 we are in a sleep phase, in which our consciousness is gradually reduced despite the fact that at the slightest stimulation we can clear ourselves. Our brain registers mainly alpha-type waves, which are the usual waves of states of relaxation even when we are awake.
Later, and if nothing interrupts it, we enter a second phase, in which the eye movements are completely reduced and there is a marked decrease in muscle tone. We are increasingly relaxed and disconnected from our surroundings. If we observe with an electroencephalogram the functioning of the brain at the level of waves, we can see how theta waves prevail, with the peculiarity that oscillations in brain activity appear in the form of K complexes and sleep spindles .
After these phases, both of light sleep, we would enter into phases 3 and 4 of sleep, known as deep sleep. These are the phases in which the organism is truly rested. Physical activity is practically non-existent for most people, although there is an increase in muscle tone . Night terrors and other parasomnias such as sleepwalking occur during these phases of sleep. Recording of brain waves would show a general prevalence of delta waves.
These phases correspond entirely to non-REM sleep. But behind them, we can still find one more phase, the REM or REM sleep.
The REM or REMP phase
The REM phase (REM stands for Rapid Eye Movement), is one of the most important phases of sleep. It is characterised by the presence of a high level of brain activity, which can be visible in the performance of rapid and constant eye movements .
It’s considered to be out of sync. The brain activity is similar to what we would have when we are awake or in the phases of sleep, with abundant sawtooth theta waves (the latter especially characteristic of the parietal areas of the brain) and beta waves. The body remains totally immobile and paralyzed, with complete disappearance of muscle tone except in the eyes and diaphragm.
It is in the REM phase of sleep that dreams and nightmares appear, as well as the ability to remember them. There is also an increase in physiological activation (despite muscular atony), increasing blood pressure, heart and respiratory rate and the appearance of erections is common. As the cycles progress, the amount of REM sleep increases.
Main function of this sleep stage
The functions of this type of sleep are not clearly defined. However, it is considered that during REM sleep we reorganize our mental contents, fixing new memories and integrating them into the memory while discarding those information or memories considered irrelevant. Thus, this type of sleep converts the experience into a memory stored in the long-term memory.
It is also during these phases that the highest level of brain development occurs, being fundamental for its maturation especially during the growth stage. It is considered to be an unsynchronized sleep.
This is not only important at a cognitive level , but also in terms of sensory processing, as studies such as those by Marcos Frank at the National Institute of Health in the United States seem to indicate, by allowing, for example, the ERK protein (a protein that is only activated in this phase of sleep) to fix the changes in the visual cortex and adjust the connections that allow visual perception to develop. The same is true for other abilities.
Evolution throughout the life cycle
Throughout life our biorhythms and our sleep cycles vary greatly . We don’t sleep the same way during our first year of life as we did in our thirties, and even less than in our eighties.
Newborns, for example, spend much of their day sleeping, with about 50% of this time in REM sleep. From the fourth month onwards this percentage drops to 40& and starts to be preceded by non-REM sleep. As the child grows, the time spent awake increases and the amount of sleep decreases. At about the age of six, sleep patterns and cycles stabilize, resembling adult sleep.
During adulthood the proportion of REM sleep is approximately 20%, the rest being non-REM sleep. With age, total sleep time is reduced and fragmented, especially when we reach old age, with a large number of nighttime awakenings . The amount of sleep is dramatically reduced, including REM sleep. Despite this, there is less latency in REM sleep (it takes less time for it to appear).
- McCarley, R.W. (2007). Neurobiology of REM and NREM sleep. Sleep Med, 8.