rapid eye movement sleep
Meaning of rapid eye movement sleep: Roughly a fifth of adult sleep, returning in longer and longer bouts so that it dominates the last hours before waking.
Definition of rapid eye movement sleep
Rapid eye movement sleep is one of the two broad kinds of sleep, set apart from non-REM sleep by darting eye movements, a fast brain wave pattern and a loss of muscle tone. It returns in cycles through the night, and each episode lasts longer than the one before, so most of it falls in the second half of the night.
How is the night organized?
Sleep runs in cycles of roughly ninety minutes, each passing through the non-REM stages and ending in an episode of this kind. The two are not spread evenly. Deep slow-wave sleep is concentrated in the first cycles, while these episodes start brief and lengthen with each cycle, so the longest of them occur shortly before waking. That is why dreams are recalled most often on waking naturally in the morning, and why an alarm set earlier than usual cuts into this stage more than into deep sleep. In adults it takes up about a fifth to a quarter of total sleep. Newborns spend close to half their sleep in it, and the proportion falls through childhood.
What is it thought to do?
The honest answer is that this is not settled. The strongest evidence supports a part in consolidating memory, particularly skills and emotionally charged material, and in processing emotional experience. Its dominance in infancy points to a role in wiring the developing brain. Studies that selectively interrupt it find effects on mood and learning, although separating those from general sleep loss is difficult.
What changes it?
| Influence | Effect |
|---|---|
| Alcohol | Suppressed early in the night, with a rebound of intense dreaming later |
| Many antidepressants | Suppressed, sometimes markedly |
| Sleep deprivation | A rebound of extra time in this stage once sleep resumes |
| Untreated sleep apnea | Breathing pauses are longest and oxygen dips deepest during it |
How is it recorded?
In a sleep study three signals are read together: brain waves, eye movements and the electrical tone of a chin muscle. The stage is scored when the brain waves look active, the eyes move in bursts and chin muscle tone reaches its lowest point of the night. That combination separates it from every other sleep stage, and the same recording identifies the disorders of REM sleep.
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Used in a sentence
Rapid eye movement sleep accounted for a reduced proportion of total sleep time on the study.
Good to know
Because the muscles that hold the upper airway open lose tone during this stage, obstructive breathing pauses tend to be longest and oxygen levels lowest while it is under way.