Rapid Eye Movements and Brain Heat
Rapid, random eye movements during sleep are probably related to increased temperature in eye-connected parts of the brain, or the speed and randomness of the molecules making it up.
“While for over 50 years, it was thought
that only mammals and birds have these distinct
neurological sleep stages, exciting new research has
shown that reptiles, fish, drosophila, octopus, and other invertebrates also display sleep states with analogous features.”
— Jaggard et al., “Non-REM and REM/Paradoxical Sleep Dynamics
Across Phylogeny” (2021)
Brain Temperature Cycles and REM
The animal brain cycles through a range of temperatures over various time periods. It gets slightly warmer and therefore more fluid, dynamic, disorderly and expansive as we wake up and go about the day, then cools down and becomes relatively solid, static, orderly and compact again when we go to sleep. The brain also heats up repeatedly throughout the night, during dreaming, random, rapid eye movement or REM sleep phases, and cools down in between, during “deep,” “slow-wave” phases.
It seems very likely brain heat itself is part of the reason why eyes move rapidly and randomly in REM sleep. There are a number of reasons to think so. One is that the eye movements are rapid. Another is that they’re random. Both of these qualities must be characteristic of temperature increases in liquid crystalline material such as that of the animal brain. If the eye movements were only rapid, one might suspect some relation to faster molecular movement in parts of the brain hooked up to the eyes. That the movements are additionally random reinforces the prospect of a causal relationship.
If true, this would be a case of brain temperature and the qualities that vary with it inducing outward animal behavior. The brain and the eyes are in extremely intimate contact, compared to the brain and other outward body parts, so it’s not difficult to imagine…