What is rem sleep?

Brain activity is quite intense at this stage.

Photo Credit: Diane Diederich
By Susan Pitman

REM, or rapid eye movement sleep, is the fifth of the five stages of sleep most people go through each night. REM is characterized by quick movements of the eyes during sleep, which is what gave this stage its name. What exactly goes on during REM? And how is it different from the other stages of sleep?

The first stage of sleep is very close to waking. During this stage, the body gradually relaxes. There may be some eye movement, but not to the extent that there is during REM sleep. If someone is awakened during this stage, he might not even be aware that he had been asleep.

The second stage is a time of light sleep, when muscles alternately relax and contract. Body temperature decreases. The heart rate slows down.

The third and fourth stages of sleep are times of deep sleep, with stage four being the deepest. The sleeper will alternate between stages three and four. During these stages, the sleeper is quite still with very rhythmic brain activity. These stages are called delta sleep.

During REM sleep, the large voluntary muscles of the body are paralyzed. Conversely, brain activity is quite intense at this stage. REM sleep is the stage of sleep when people dream. It is thought by sleep researchers that the paralysis of the large muscles occurs to keep people from acting out their dreams. REM sleep is sometimes called paradoxical sleep, due to the contrast between the high brain activity and the physical immobility of the sleeper.

During REM sleep, breathing and heart rate are faster than normal. The sleeper’s legs, face, and fingers twitch. And of course, there is rapid movement of the eyes. This is the stage of sleep when people have intense dreams, although they might not remember the dreams upon waking.

The stages of sleep proceed in cycles throughout the night. The cycles might repeat as many as five times per night. The length and intensity of REM sleep increases with each succeeding cycle. During the first cycle, REM sleep might be only 10 minutes long, while during the last cycle it might stretch to 90 minutes.

The duration of REM sleep is affected by physical and psychological factors, as is the quickness of its onset. People who are depressed have shorter REM stages than normal. However, people who are being treated for depression with drugs like Prozac often have longer REM cycles. Narcolepsy, a sleep disorder where a person may fall asleep for short periods of time at unexpected times, may delay the onset of REM sleep. People with narcolepsy have also been shown to exhibit signs of REM sleep disorder. In this disorder, the person’s large voluntary muscles are not paralyzed and they attempt to act out their dreams, often quite violently.

The proportion of time spent in REM sleep during the sleep cycle is highest when a person is a baby or small child. The proportion of REM sleep drops off further with adolescence, and further still in old age. However, the lengthening of the REM cycle comes with old age.

REM has been shown to have links to memory consolidation and to learning. People who are deprived of REM sleep through sleep deprivation might have problems remembering. They also might have trouble learning new things.