Discovery and the sleep cycle
In 1953 University of Chicago graduate student Eugene Aserinsky and his adviser Nathaniel Kleitman noticed recurring periods in which sleepers' eyes moved rapidly, and called them rapid eye movement sleep. William Dement then showed that people woken during these periods vividly recalled dreams. Sleep descends through light N1 and N2 into deep slow-wave N3, then rises into REM, a cycle of about 90 minutes repeated four to six times a night. Deep sleep dominates early in the night and REM periods lengthen toward morning, so going to bed late or waking early cuts REM disproportionately.
| Stage | Features |
|---|---|
| N1 | Transition into sleep; easily woken |
| N2 | About half of sleep; sleep spindles |
| N3 (slow-wave) | Deepest sleep; growth hormone release |
| REM | Rapid eye movements, muscle atonia, vivid dreams |
What REM does
During REM the brain's oxygen use and activity resemble wakefulness, but the brainstem blocks motor signals to the spinal cord so the limbs barely move — a safeguard against acting out dreams. Research links REM to consolidating skills and information learned during the day and to softening the emotional edge of memories. Newborns spend about half their sleep in REM, tying it to brain development. In depression REM tends to start unusually soon after falling asleep, and many antidepressants suppress it. Alcohol helps people fall asleep faster but suppresses REM early in the night and causes early-morning waking.
Sleep paralysis and REM sleep behavior disorder
If REM's muscle paralysis lingers briefly after waking, you can be conscious but unable to move: sleep paralysis. It is usually harmless and more common with sleep deprivation and irregular schedules. The opposite problem, in which paralysis fails and people physically act out dreams, is REM sleep behavior disorder, first described in 1986 by Carlos Schenck and colleagues in Minnesota. Sufferers may shout or punch in their sleep and injure themselves or a partner. It is most common in men over 50 and often precedes Parkinson's disease or Lewy body dementia by years, making it an important early sign; a sleep study is recommended.
This article is general health information and is not a substitute for diagnosis or treatment. If symptoms persist, see a doctor.
FAQ
- How much REM sleep do I need?
- Adults typically spend 20–25% of sleep in REM — about 1.5–2 hours in a 7–8 hour night. Getting enough regular sleep matters more than trying to boost REM alone.
- If I don't remember dreams, am I missing REM?
- No. Everyone has REM every night, but dreams are mostly forgotten unless you wake during or right after a REM period.
Sources reviewed: 2026-10-26
References
- Aserinsky, E., & Kleitman, N. (1953). Regularly occurring periods of eye motility, and concomitant phenomena, during sleep. Science, 118(3062), 273–274.
- Dement, W., & Kleitman, N. (1957). The relation of eye movements during sleep to dream activity. Journal of Experimental Psychology, 53(5), 339–346.
- Schenck, C. H., et al. (1986). Chronic behavioral disorders of human REM sleep. Sleep, 9(2), 293–308.
- Walker, M. P. (2017). Why We Sleep. Scribner.