What Is Rapid Eye Movement Sleep? What Is REM?

Date: Jul-17-2012Rapid eye movement sleep, or REM, is one of the five stages of sleep that most people experience nightly. It is characterized by quick, random movements of the eyes and paralysis of the muscles. The amount of time spent in REM sleep varies significantly with age; it normally makes up around 20-25% of an adult humans total time spent asleep (on average about 90-120 minutes), and approximately 80% of a newborn's.

People usually experience REM sleep 4 or 5 times a night (it comes in cycles), the first cycle - which occurs at the beginning of one's sleep - only lasts for a short time, with each following cycle being a little longer.

It is common for some people to experience light sleep, or even to wake up after a cycle. The amount of time one spends in REM sleep has a lot to do with certain psychological factors - people with depression tend to be in the state for a shorter duration than those without it.

Studies have shown that people who go to sleep after being sleep deprived enter REM sleep faster than those who weren't.

While in REM sleep, most of the muscles become paralyzed and the activity of the brain's neurons becomes quite intense, similar to the activity during wakefulness. This is why REM sleep is sometimes known as paradoxical sleep. It's during this stage of sleep that most people are able to have especially vivid dreams.

Physiology of REM Sleep
During REM, certain neurons in the brain stem, called REM sleep-on cells, become especially active - these cells are most likely what trigger this phase in the sleep cycle.
Once triggered and in a state of REM, the body stops releasing neurotransmitters - called monoamines - that are responsible for stimulating the motor neurons; this means that the muscles stop moving, essentially entering a state of temporary paralysis.

Some people don't experience the paralysis, their muscles continue to move, even while they are in REM sleep. They may act out their dreams in violent or dramatic ways, this is a condition called REM behavior disorder (RBD). (Link to article)
Functions of REM Sleep
Memory Consolidation

One theory states that REM sleep is important for the consolidation, or stabilization of spacial and procedural memory. However, there are doubts as to the validity of such claims, given that tricyclic antidepressants and monoamine oxidase (MAO) inhibitors, that reduce the amount of REM sleep someone gets, have been found not to have any negative effects on memory.

Mitchison and Crick, in their hypothesis of sleep and neural networks, proposed that REM sleep can help eliminate abnormal modes of interaction in the neural networks of the cerebral cortex.

Stimulation of Central Nervous System (CNS) Development

Another theory, called the Ontogenetic Hypothesis of REM sleep, says that this sleep stage is vital for the development of the human brain in infants. It proposes that REM sleep is responsible for the neural stimulation necessary to develop mature neural connections.

Supporting evidence for this is seen in how the number of hours spent in REM sleep reduces as one ages, and how sleep deprivation in early life can be a cause of behavioral problems, sleep disruption and decreased brain mass. This theory suggests that REM sleep might not have any essential role in mature human brains.
Creativity and REM Sleep
REM Sleep facilitates the way creativity combines certain associative elements into new combinations that are necessary or helpful for problem solving. This has been attributed to the cholinergic and noradrenergic neuromodulation that occurs while someone is in a REM state. Feedback from the hippocampus to the neocortex is reduced during REM sleep, and the low levels of acetylcholine and norepinephrine in the neocortex promote increased associational activity in the neocortical areas.

Written by Joseph Nordqvist

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