Psyfield

    简 繁

    Topics

    All terms About

    Sleep stages

    睡眠阶段

    Concept
    Also called
    sleep cycle, REM sleep, NREM sleep, non-REM sleep

    Sleep is divided into three stages of non-rapid eye movement (NREM) sleep, N1 to N3, and rapid eye movement (REM) sleep. Each has its own brain-wave pattern, and the stages repeat in cycles through the night.[1][2]

    Select a stage on the left for details. The chart sketches a typical 8-hour adult night: deep sleep comes early, and REM periods lengthen toward morning.
    A sketch of a typical adult night: cycles of about 90 minutes, deep sleep early, REM periods growing longer. Point at or tap parts of the figure for details
    A sketch of a typical adult night: cycles of about 90 minutes, deep sleep early, REM periods growing longer. Save as image (PNG)

    Key points

    • N1 is light sleep (about 5% of adult sleep); N2 brings sleep spindles and K-complexes (about 45%); N3, deep sleep, is dominated by slow, high-amplitude delta waves (about 25%).[1]
    • REM (about 25%) brings rapid eye movements, wake-like brain waves and slack skeletal muscles except the eyes and diaphragm. People woken from REM usually report dreams.[1][3]
    • Eugene Aserinsky and Nathaniel Kleitman first described REM periods in 1953; 20 of 27 awakenings during eye movements produced detailed dream reports.[3]
    • A cycle averages about 90 minutes and repeats 4 to 6 times a night. Deep sleep dominates early; later, REM periods lengthen until morning sleep is mostly N1, N2 and REM.[1][2]

    An example

    Ms. Wang’s alarm goes off at 2 a.m. and she wakes groggy, with no dream to recall. At 6 a.m. she wakes on her own in the middle of a vivid dream. The first waking most likely came from deeper NREM sleep, the second from REM.

    Misreadings and limits

    REM sleep is often mistaken for deep sleep. The deepest stage is N3, with slow, high-amplitude delta waves. During REM the brain is nearly as active as when awake, and it is not considered a restful stage for the body.[1]

    Sources

    1. 1 Patel, A. K., Reddy, V., Shumway, K. R., & Araujo, J. F. (2024). Physiology, sleep stages. StatPearls. StatPearls Publishing (NCBI Bookshelf NBK526132). View source
    2. 2 Eunice Kennedy Shriver National Institute of Child Health and Human Development (2019). What happens during sleep?. NICHD, National Institutes of Health. View source
    3. 3 Aserinsky, E., & Kleitman, N. (1953). Regularly occurring periods of eye motility, and concomitant phenomena, during sleep. Science, 118, 273–274. View source

    Last checked against sources: October 26, 2026