What is REM Sleep?

REM sleep is one of five sleep stages. The term REM is an anachronism for Rapid Eye Movement, since constantly moving eyes are one of the primary physical signs that a person is in REM sleep. A sleeper’s eyes move rapidly in many directions under the lids, presumable as they view events occurring in a dream.

Stages of Sleep

REM is a unique sleep stage. So much so that the other four stages are collectively called non-REM sleep. Each non-REM stage lasts 5 to 15 minutes. The non-REM sleep states collectively last approximately 90 minutes.

The stages of sleep are not assigned arbitrarily. There are clear biological and physical symptoms, plainly observable through the use of a polysomnograph. Sleep studies taken with the device are called polysomnography or PSG. Doctors and scientists use these studies to help diagnose sleeping disorders.

The polysomnograph uses multiple sensors placed on the head to record brain waves, while another sensor is placed on the ear to get a neutral reading for comparison. One or two sensors are placed near the eyes to measure eye movement, while elastic belts around the waist and stomach measure breathing. Electrodes attached to the chin monitor relaxation or tone in muscles. Sensors on the chest monitor the heart rate, while an oximeter is placed on the finger or earlobe to measure blood oxygen. Studies often use video cameras to monitor the sleeper’s movement and body position as well.

Signs of the Sleep Stages


During the night, people rotate through the five stages of sleep, referred to as the sleep cycle. The cycle can occur up to five times each night. Each successive cycle produces a longer and deeper REM stage. The first REM cycle may only be ten minutes, while the longest and final cycle can be as long as 90 minutes.

In the first stage of sleep, the body begins to relax and the mind feels drowsy. It is the grey area between sleep and wakefulness. You may still be conscious of your thoughts during this time and there may be some minor eye movement. A polysomnograph shows that brain activity slows as much as 50% during stage one. This stage has no restorative properties and lasts for about ten minutes. A sleeper disturbed from stage one sleep will not feel as though he or she has slept at all.

The second stage is light sleep. Your body temperature falls and your heart rate slows. During stage two, a polysomnograph will show intermittent peaks and troughs, as muscle tone repeatedly intensifies and relaxes.

During the third and forth stages, you are deeply asleep. Stage four is deeper than stage three. Stages three and four are sometimes referred to together as delta sleep, with notable slow and rhythmic brain activity. Once the sleeper reaches stage four, the sleeper reverts back to stages three and then two, before finally falling into REM sleep.

Time for Dreams

REM is the fifth and deepest stage of sleep. In order to prevent dreamers from injuring themselves, the brain has developed a mechanism for paralyzing the large voluntary muscles of the body. During this time, the brain is intensely active as dreams roll into the mental landscape. The paradox of the still body and active mind has spurred some to call REM paradoxical sleep.

The REM brain wave patterns are similar to those seen in the more alert stage one. While the large voluntary muscles remain paralyzed, the face, fingers and legs will often twitch. The sleeper’s heart rate increases as well, while the eyes engage in rapid movements in all directions. The dreams that occur during REM may be quite intense, but sleepers often lose memory of the dream upon waking.

REM Disorder

Some people’s brains fail to shut down the major voluntary muscles during REM sleep. The disorder is called RBD or REM Behavior Disorder. With RBD, the sleeper kicks and flails about wildly, while acting out a dream. The disorder is thankfully rare. It can lead to disastrous consequences if the sleeper runs down the stairs during a dream. These movements sometimes can be violent and injurious to others as well. There are several medications that may help with RBD, but none are 100% successful.

Necessity of REM?

Scientists still debate whether REM sleep is necessary or not. There have been cases of people who are incapable of attaining REM sleep with no ill effects whatsoever. Other studies suggest those who do not reach REM sleep may suffer learning or memory difficulties. No solid proof has emerged for either case.