Sleep science

What happens in the brain during REM

Not "the brain switches on". Some regions run close to waking levels, others go quieter than in deep sleep, and the pattern explains most of what dreams are like.

7 min readbeginnerStrictly reviewed · cited

The useful thing about REM is not that the brain is active. It is that the activity is uneven, and the shape of that unevenness predicts the character of dreams surprisingly well.

What goes up

Imaging studies through the 1990s found strong activity in:

  • Limbic and paralimbic regions: the amygdala and surrounding structures, heavily involved in emotion. This is the finding that most directly matches the experience: dreams are emotional out of proportion to their content, and fear is the most reported dream emotion.
  • Visual association cortex: the areas that assemble complex visual scenes, as opposed to the primary visual cortex that receives input from the eyes.
  • The pons and midbrain, driving the state from the brainstem.

What goes down

  • Dorsolateral prefrontal cortex: working memory, planning, self-monitoring, "wait, that is not right". Relatively deactivated.
  • Primary visual cortex. You are not seeing; you are constructing.

Why that combination produces dreams

Put those together and you get the standard dream: vividly visual but not perceived, strongly emotional, and accepted without question. The regions that would normally object are the quiet ones.

It also explains why lucidity is unusual and effortful. Becoming lucid involves the very prefrontal machinery that REM has turned down, which is why the lucid state shows up in imaging as prefrontal regions coming back.

The honest caveat

These are group-level findings from small samples using PET and fMRI, and "region X is active" is a coarser statement than it sounds. The broad pattern (hot limbic, cool executive) is well replicated. The details are still argued about.

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.Functional Neuroanatomy of Human Rapid-Eye-Movement Sleep and DreamingPeer-reviewed research

    Pierre Maquet and colleagues (1996) · Nature

    Cited for: PET evidence that limbic and paralimbic regions are strongly active during REM while parts of the prefrontal cortex are relatively deactivated.

  2. 2.Regional Cerebral Blood Flow Throughout the Sleep-Wake Cycle: An H2(15)O PET StudyPeer-reviewed research

    Allen R. Braun and colleagues (1997) · Brain

    Cited for: That REM is not uniform activation: visual association areas are active while primary visual cortex and executive prefrontal regions are not.

  3. 3.Dreaming and the Brain: Toward a Cognitive Neuroscience of Conscious StatesPeer-reviewed research

    J. Allan Hobson, Edward Pace-Schott and Robert Stickgold (2000) · Behavioral and Brain Sciences

    Cited for: A synthesis of the brain-state differences between waking, REM and non-REM, and what they predict about the character of dreaming in each.