REM sleep

American  

noun

Physiology.

1. a recurrent period of sleep, typically totaling about two hours a night, during which most dreaming occurs as the eyes move under closed lids and the skeletal muscles are deeply relaxed.

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REM sleep Scientific  

/ rĕm /

1. Short for rapid eye movement sleep. A period of sleep characterized by rapid periodic twitching movements of the eye muscles and other physiological changes, such as accelerated respiration and heart rate, increased brain activity, and muscle relaxation. REM sleep is associated with activity in the pons of the brainstem; when the pons is eliminated, REM sleep does not occur. REM sleep is the stage of sleep in which most dreaming takes place and is thought to allow for the organization of memories and the retention of learning. REM sleep is the fifth and last stage of sleep that occurs in the sleep cycle, which repeats itself about five times throughout a period of sleep. It is preceded by four stages of non-REM sleep. REM stages become longer with each cycle and account for about 20–25 percent of total sleep in adult humans. In infants, roughly 50 percent of sleep is REM sleep, which is believed to be necessary for the maturation of the central nervous system.

2. Compare non-REM sleep See more at sleep

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Etymology

Origin of REM sleep

First recorded in 1965–70

Example Sentences

The anesthetized patients’ brains produced activity that shared similarities to being unconscious in a coma—as well as deep sleep, REM sleep and patterns unique to anesthesia.

From The Wall Street Journal • Jun. 3, 2026

During REM sleep, both hormones increase, leading to a surge in growth hormone.

From Science Daily • Mar. 30, 2026

REM sleep, often referred to as dream sleep, supports emotional regulation, motor skill development, and brain growth.

From Science Daily • Feb. 4, 2026

Let me get real deep real quick before I go into this REM sleep.

From Los Angeles Times • May 9, 2025

My mother is the only individual I know who can fall asleep instantly for two minutes—deep REM sleep, complete with snoring—only to be awakened instantly by certain select noises.

From "The Color of Water: A Black Man's Tribute to His White Mother" by James McBride