What a strange theory about REM sleep tells us about building AI that doesn’t quietly fall apart
Put a blindfold on a sighted adult and stick them in an fMRI scanner. Get them to feel some textured surfaces with their fingers. Then watch what happens in their visual cortex, the part of the brain that is supposed to be doing absolutely nothing in the dark. It lights up. Not after weeks, not after days, but after about forty-five minutes.
That finding, which has been replicated in various forms since the early 2000s, is one of the more unsettling results in modern neuroscience. The visual cortex is not a quiet, dormant region waiting patiently for the lights to come back on. The moment you stop using it for vision, the neighbours start moving in. Touch first, then hearing. Within an hour, real estate that was supposed to be reserved for processing photons is being repurposed for something else entirely.
This raises an obvious and slightly alarming question. If your visual cortex starts getting taken over within an hour of going dark, what happens every single night when you close your eyes for eight hours?
A neuroscientist named David Eagleman thinks he has the answer, and it is one of the more interesting hypotheses about why we dream that has come along in a while. He calls it the defensive activation theory, and once you understand it, you start seeing the same pattern everywhere, including in some surprisingly broken corners of how we currently build AI.
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