Psychedelic compounds act on the brain by binding to serotonin receptors. Scientists have identified at least 14 different receptors that respond to the neurotransmitter serotonin. Among them, psychedelics most strongly target the 2A receptor. This receptor plays several roles, including reducing activity in visual regions of the brain and influencing learning.

“We have observed in earlier studies that visual processes in the brain are suppressed by this receptor,” says Callum White, first author of the study. “This means that visual information about things happening in the outside world becomes less accessible to our consciousness. To fill this gap in the puzzle, our brain inserts fragments from memory – it hallucinates.”

When outside visual input becomes weaker, the brain compensates. Instead of relying fully on incoming signals, it pulls pieces from stored experiences. Those memory fragments blend into perception, producing hallucinations.