Britannica Sources used in this answer

How do REM sleep and NREM sleep differ?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

Hear how scientists are studying the sleep-related brain activity of animals and migratory birds — sleep Find out how scientists are studying the sleep activity of migratory birds.

The human sleep cycle consists of two distinct phases: rapid eye movement (REM) sleep and non-rapid eye movement (NREM) sleep. A typical cycle lasts 90 to 110 minutes, and adults generally complete four to six cycles per night.12

NREM Sleep

NREM sleep is considered the quiet or restful phase and is subdivided into three stages (N1, N2, and N3).1
* Characteristics: It is associated with decreased autonomic nervous system activity and reduced brain activity, particularly in the thalamus and frontal cortex.1
* Function: It is theorized to serve as a state of bodily repair and is linked to memory consolidation.1
* Parasomnias: Disruptive events such as sleepwalking and sleep terrors occur during NREM stages.12

REM Sleep

REM sleep is a state of high physiological activation, often called "paradoxical sleep" because its EEG patterns resemble those of wakefulness.32
* Characteristics: It features irregular eye movements, elevated brain activity, and atonia—a temporary paralysis of skeletal muscles that prevents individuals from acting out dreams.32
* Function: It is often associated with "brain repair," emotional regulation, and vivid dreaming.312
* Physiology: Unlike NREM, REM sleep involves increased heart rate, blood pressure, and oxygen consumption.32