The Big Picture
REM sleep was discovered in the 1950s in a Chicago sleep lab, when researchers noticed sleepers' eyes darting beneath their lids [1][3]. Andrew Huberman describes those movements as erratic and in all directions, driven by waves of activity from the pons in the brainstem, through the thalamus, to the cortex [1][3]. During REM we are paralyzed, a state called atonia, and dreams feel like hallucinations [1].
The sources look at REM from two angles. Huberman's central point is chemical: epinephrine, which he calls the chemical signature of fear and anxiety, is absent in REM, so the brain can replay real events, and elaborate distortions of them, without the emotion of fear attached [1][3]. The Huberman Lab episode with Matthew Walker covers REM's structure and its place in human evolution: REM has two phases with different rates of dream recall, and Walker cites work by Charles Nunn in which humans average far more of their sleep as REM than most primates do [2].
Where the Experts Agree
- Eye movements. Huberman says they are erratic, go in all directions and are driven by brainstem activity [1][3]. Walker says that, despite the old idea that the eyes are tracking dream scenes, careful analyses do not show a strong correlation between eye movements and what is seen in the dream [2].
- Muscle control. Huberman describes paralysis in REM, called atonia [1]. The Walker episode likewise notes that REM sleep brings loss of muscle tone [2].
- Dreaming. Huberman says dreams in REM feel like hallucinations [1]. The Walker episode reports dream recall of around 80% from the tonic phase of REM, which has no eye movements, and 95 to 100% from the phasic phase, which has the darting eye movements [2].
- The value of sleep. Huberman says more sleep is always better than less [3]. Walker describes 1980s rat studies, which he notes have not been replicated for ethical reasons, in which rats totally deprived of sleep died in roughly 13 to 17 days, almost as fast as with food deprivation [2].
Where They Differ
The passages show different emphases rather than a disagreement: Huberman's are about the chemistry of REM and what it does for emotion [1][3], while the Walker episode is about REM's phases, how much of it humans get and whether it sustains life [2].
For Huberman, the absence of epinephrine is the key [1]. Because the brain can replay events without fear attached, he says REM is so important for adjusting our emotional relationship to challenging things that happened while we were awake, from social anxiety to dreams of being late for an exam or naked in public [3]. He also covers the earlier part of the night: a motor skill learned during the day is consolidated primarily early in the night, and slow wave sleep is important for learning specific details about specific events [1].
The Walker episode turns to how much REM humans get [2]. Citing the work of Charles Nunn, Walker says most primates average about 9% of their sleep as REM while humans average about 20%, which makes us a single data point far off the curve [2]. Why remains unclear [2]. One idea, presented as speculative, is the move from trees to the ground: loss of muscle tone is risky 30 feet up on a branch, and coming down may have allowed more REM [2].
Only Huberman's passages address nightmares. He says the research suggests that intense fearful dreams, such as the common dream of being chased while unable to move, probably happen in slow-wave sleep, not REM, precisely because norepinephrine is absent in REM [3].
Practical Takeaways
- Get more sleep rather than less: Huberman says more is always better [3].
- Don't worry too much about one short night before a physical event; Huberman says people often worry about this more than they need to [3].
- Remember that a new motor skill, such as a dance move learned during the day, is consolidated primarily early in the night, according to Huberman [1].
- Know that slow wave sleep also has a job: Huberman says it is important for learning specific details about specific events [1].
- Think of REM as the time when the brain can replay difficult events without fear attached, which is why Huberman calls it so important for adjusting our emotional relationship to challenging experiences [3].
- If you have an intensely fearful dream of being chased while unable to move, Huberman says the research suggests it probably happened in slow-wave sleep, not REM [3].
- Don't assume darting eyes mean a sleeper is watching a dream: Walker says careful analyses do not show a strong correlation between eye movements and what is seen in the dream [2].
- Expect the body to be still in REM: Huberman says we are paralyzed in this state, which is called atonia [1].
