Non-REM sleep

Non-REM sleep (or NREM) is, collectively, sleep stages 1–3, previously known as stages 1–4. Rapid eye movement sleep (REM) is not included. There are distinct electroencephalographic and other characteristics seen in each stage. Unlike REM sleep, there is usually little or no eye movement during these stages. Dreaming is rare during NREM sleep, and muscles are not paralyzed as in REM sleep. People who do not go through the sleeping stages properly get stuck in NREM sleep, and because muscles are not paralyzed a person may be able to sleepwalk. In more detail, NREM consists of three separate stages:

• Stage 1, which is light sleep
• Stage 2, or baseline sleep, which is 45–55% of total sleep in adults
• Stage 3, which is deep sleep, where parasomnias occur

Stages

Stage 1

In this stage, the brain produces high amplitude theta waves (slow brain waves), which are very irregular brain waves that are even slower than beta waves. This period of sleep lasts only a brief time (around 5–10 minutes). If aroused from this stage of sleep, a person may feel as if they have not slept. Stage 1 may last for five to 10 minutes. Many may notice the feeling of falling during this stage of sleep, which may cause a sudden muscle contraction (called hypnic myoclonia).

Stage 2

This is the first stage of true sleep, lasting from 10 to 25 minutes. The brain begins to produce bursts of rapid, rhythmic brain wave activity known as sleep spindles. Body temperature starts to decrease and heart rate begins to slow.

Stage 3

Deep, slow brain waves known as delta waves begin to emerge during this stage. It is a transitional period between light sleep and a very deep sleep. It's also the period where the body repairs and regrows tissues, builds bone and muscle, and strengthens the immune system. As you get older, you sleep more lightly and get less deep sleep.

See also

• Sleep
• Sleep disorder
• Sleep deprivation
• Sleep medicine
• Sleep paralysis
• Sleepwalking
• Rapid eye movement sleep