Why Our Dreams Are Visual

A theory holds that dreams are a way for the visual cortex of the brain to “defend its turf” against being “taken over” to process inputs from other senses.

Why Do We Dream? Maybe to Ensure We Can Literally ‘See’ the World upon Awakening

A theory holds that dreams are a way for the visual cortex of the brain to “defend its turf” against being “taken over” to process inputs from other senses

Scientific AmericanRoberta McLain

What’s the visual equivalent of “in one ear and out the other”? Sometimes when I’m reading I suffer from that. I remember around maybe 1st or 2nd grade, having to read something for school, my father sat there and listened. Once I’d finally finished, he asked me what it was about. “I don’t know; I wasn’t paying attention.” I think he laughed at that. I read it, as instructed. Anyway, this topic, explaining the plasticity of the brain — how if some function, such as visual processing, wants to keep its territory, it must keep using its territory or it’ll be assigned to another task — was captivating and has stuck with me ever since.

If you’re sleeping a third of each day, other functions like hearing or touch might muscle out visual processing. To counteract this, your brain dreams visually, which helps maintain that compute capacity. The amount of REM sleep you need correlates to the plasticity of your brain: babies need lots; old people, less.

A related study blindfolded one group while they and several other groups engaged in learning brail (or some other touch-based activity). The blindfolded group excelled. As I recall, at the end of the study, with the blindfolds gone, that group’s lead diminished to par. However, the effects of non-use were noticeable in as little as forty-five minutes.

I wonder sometimes when I feel frustration at a learning curve, if that’s me literally fighting the decreasing plasticity of my brain. I should probably do that more.

The Defensive Activation Theory: REM Sleep as a Mechanism to Prevent Takeover of the Visual Cortex - PubMed

Regions of the brain maintain their territory with continuous activity: if activity slows or stops (e.g., because of blindness), the territory tends to be taken over by its neighbors. A surprise in recent years has been the speed of takeover, which is measurable within an hour. These findings lead u …

PubMedDavid M Eagleman

We suggest that the brain combats neuroplastic incursions into the visual system by keeping the occipital cortex active at night. We term this the defensive activation theory. In this view, REM sleep exists to keep the visual cortex from being taken over by neighboring cortical areas. After all, the rotation of the planet does not diminish touch, hearing, or smell (e.g., you detect if a bug crawls on you, your baby cries out, or there is the smell of smoke). Only visual input is occluded by darkness.

It's an interesting theory!