Perception as Prediction
Modern neuroscience increasingly views perception not as passive reception of sensory data from the outside world, but as active prediction — the brain constantly generating models of what it expects to experience, and updating those models based on incoming sensory information. Under normal conditions, predictions and incoming data stay in rough alignment. Consciousness feels like an accurate representation of the outside world because the brain's predictions are continuously corrected by sensory reality.
Psychedelic compounds appear to disrupt this balance. New research in mice suggests that substances like psilocybin and LSD do not create hallucinations by generating random perceptual noise, as was once thought. Instead, they alter the balance between prediction and sensory input — causing the brain to weight its stored memories and internal models more heavily than the actual signals coming in through the senses.
The Study
The research used a combination of behavioral testing and neural recording to examine how psychedelics change visual processing in mice. Mice trained to respond to specific visual patterns were given psychedelic compounds and then re-tested. The key finding: mice under the influence of psychedelics were more likely to respond to visual stimuli as though they were familiar patterns from memory, even when the actual stimulus was different.
Neural recordings revealed changes in the balance of activity between areas of the visual cortex associated with bottom-up sensory processing — reading incoming signals from the eyes — and areas associated with top-down prediction and memory. Psychedelic administration appeared to shift this balance toward top-down processing, effectively causing the brain to project its internal models onto the world.
