What Is REM Sleep?

What is REM sleep? How does it relate to learning and brain development? How does it evolve over the years? Find out in today's article.
What Is REM Sleep?
Laura Ruiz Mitjana

Written and verified by la psicóloga Laura Ruiz Mitjana.

Last update: 16 April, 2023

During the night, we go through different stages of sleep; one of them is REM sleep. Also called paradoxical sleep or rapid sleep, it’s the time when the eyes move rapidly, the body is immobile and paralyzed, and breathing may be agitated.

It’s the phase in which we dream and in which we have nightmares and other types of parasomnias. Having energy and being rested have a lot to do with the quality of sleep. People who suffer from some type of rest disorder or problem may notice how their day-to-day life is interfered with, either because they feel more tired or because they experience a lack of energy.

Do you want to know more about this type of sleep? What kind of brain activity occurs when we’re immersed in it? Why is this phase so important? Keep reading to find out!

What is REM sleep?

This phase, according to the classification of Dement and Kleitman (1957), is the second stage of sleep. First, we find the non-REM phase (slow sleep) which, in turn, is divided into four subphases. After these four comes REM sleep, also called paradoxical sleep or rapid sleep.

The REM phase is one of the most important, as it’s where the consolidation of what has been learned during the day and brain development take place.

Rapid eye movement occupies 20% of the total time of the phases. We go through the REM phase about four or five times a night, as each rest is completed with four or more sleep cycles (in each cycle, we go through all the phases). The first few times, we go through REM sleep, we do it briefly, but as the night goes on, the episodes get longer.

Electroencephalogram during sleep.
Brain waves are different according to the phase of sleep that a person is going through.

What happens during REM sleep?

REM sleep stands for rapid eye movement, that is, rapid eye movements. During this phase, a series of phenomena occur, such as the following:

  • Increases the activity of the sympathetic nervous system.
  • Significant muscle atony occurs: The body is immobile and paralyzed.
  • The waves of the electroencephalogram (EEG) are of mixed frequencies and low voltage: So-called sawtooth waves and PGO spikes appear.
  • Rapid eye movements occur: Although we have our eyes closed, their movement is rapid and incessant.
  • Heart rate accelerates, blood pressure increases, and respiratory disturbances occur.
  • Nightmares and fundamental dream activity appear.
  • There are erections.

What brain activity occurs?

During this type of sleep, brain activity is very similar to what we’d have while awake. In other words, it’s very active.

REM activity also resembles that produced in the initial phases of sleep. In other words, when we fall asleep (non-REM phase). In REM sleep, there’s desynchronization at the level of brain waves; Theta and beta waves predominate. Sawtooth and PGO spikes appear.

What function does REM sleep have?

Although the function of REM sleep hasn’t been exactly determined, there’s talk of a possible consolidation of learning at this stage, as well as development at the brain level. In other words, according to the hypotheses, in REM sleep, we fix the new memories created during the day and integrate them into memory.

In other words, during this sleep stage, the brain converts experiences into memories and stores them in long-term memory. In addition, at this stage, the brain may discard information or memories that it considers irrelevant.

As for the development of the brain, during REM sleep, it could mature, especially in the case of very young children. In this regard, according to the Instituto del Sueño (the Sleep Institute), the REM phase occupies most of the night during the first years of life, and that would be essential.

Sensory processing

On the other hand, this type of sleep could also be related to sensory processing. Along these lines, studies carried out by Marcos Frank of the National Institute of Health of the United States demonstrated that REM sleep allows the ERK protein to finish fixing changes in the visual cortex and adjusting the connections necessary for visual perception to develop.

The appearance of parasomnias

We’ve mentioned that nightmares and dreams frequently appear during REM sleep. We’re actually talking about parasomnias, which are behavioral disorders or abnormal, unexpected, inopportune, or undesirable behaviors that occur at the onset of sleep, during sleep, or upon awakening.

According to the sleep guide prepared by the Spanish Sleep Association and the Government of Aragon, we find two types of parasomnias: Those associated with NON-REM sleep (sleepwalking, night terrors, and confusional awakenings) and those associated with paradoxical or REM sleep. As for the latter, they include the following:

  • Nightmares: They’re extremely unpleasant or terrifying dreams, as well as long ones, that leave a vivid memory. They appear in the second half of the night.
  • Sleep paralysis: This is a very brief episode that occurs during the transition period between the dream state and the waking state. The person is awake and can see and hear, but is unable to voluntarily move any part of their body.
  • Sleep behavior disorders: According to the DSM-5, these are repeated episodes of awakening during sleep associated with vocalization and complex motor behaviors.
Nightmares in REM sleep.
Nightmares are long, terrifying dreams that occur during REM sleep.

How does REM sleep evolve throughout the life cycle?

As we’ve mentioned, the rapid eye movement phase occupies most of the night in the first years of life. The duration is shortened as the person grows older. Newborns spend half the night at this stage, but from the fourth month of life, the percentage drops to 40%.

At 6 years of age, sleep patterns stabilize, as well as cycles. At that age, we can say that sleep is similar to that of an adult and that the REM phase occupies 20% of the total night.

As we grow older, as we indicated, the hours of sleep decrease and are increasingly fragmented. This is especially accentuated in advanced ages with a large number of nocturnal awakenings.

Therefore, in the stage of old age, rapid eye movement sleep is diminished. At the same time, at this stage, the latency of paradoxical or rapid sleep is shorter, that is, it takes less time for this phase to appear when we fall asleep.

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