Sleep science

What is REM sleep?

The stage most associated with vivid dreaming, what actually happens during it, and why your body is paralysed while it runs.

7 min readbeginnerStrictly reviewed · cited

Rapid eye movement sleep was identified in 1953, when Aserinsky and Kleitman noticed periods during sleep when sleepers' eyes moved rapidly under closed lids, and found that waking someone during those periods produced detailed dream reports far more often than waking them at other times.

That single observation founded modern sleep science.

What happens during REM

  • Brain activity rises to levels close to waking in many regions.
  • The body is paralysed. Motor output is actively inhibited at the brainstem. This is REM atonia, and it is why you do not act out your dreams.
  • Breathing and heart rate become irregular.
  • The eyes move, in bursts, which is where the name comes from.
  • Prefrontal regions associated with critical judgement are relatively less active, which is the leading account of why dreams seem plausible while you are inside them.

REM is not the whole story

Dreaming is not exclusive to REM. Reports can be gathered from non-REM sleep too, though they tend to be shorter, less vivid and less narrative. The old equation "REM equals dreaming" is a simplification.

Why the atonia matters for this site

REM atonia explains a surprising amount of the dream vocabulary. Running in slow motion, punches with no force, screaming with no sound: all are consistent with motor commands being issued and blocked, producing effort without feedback.

It also explains sleep paralysis, which is what happens when the atonia persists into waking.

Sleep-science pages summarise published research for general education. They are not a substitute for a clinician. If a sleep problem is affecting your health, speak to a doctor, and never change prescribed medication because of something you read here.

Sources and reviewed references

3 references. What these labels mean

  1. 1.Regularly Occurring Periods of Eye Motility, and Concomitant Phenomena, During SleepPeer-reviewed research

    Eugene Aserinsky and Nathaniel Kleitman (1953) · Science

    Cited for: The discovery of REM sleep and its association with dream recall, the founding observation of modern sleep science.

  2. 2.The Brain as a Dream State Generator: An Activation-Synthesis Hypothesis of the Dream ProcessPeer-reviewed research

    J. Allan Hobson and Robert McCarley (1977) · American Journal of Psychiatry

    Cited for: The activation-synthesis model: that dream narrative is partly the forebrain making sense of brainstem-generated activity.

  3. 3.Sleep Paralysis and the Structure of Waking-Nightmare HallucinationsPeer-reviewed research

    J. Allan Cheyne (2003) · Dreaming

    Cited for: The three-factor structure of sleep-paralysis hallucinations (intruder, incubus and vestibular-motor experiences) which accounts for the recurring "presence in the room" and "pressure on the chest" reports.