When serotonin dims the light: 5-HT2A receptor suppresses visual input, offering a mechanism for LSD-like hallucinations

5-HT2A serotonin receptors can suppress incoming visual information while leaving other parallel brain processes intact. Researchers at Ruhr-University Bochum used fast, light-controlled activation of receptor function in mouse visual cortex. By effectively turning 5-HT2A on and off like a switch, they found that increased 5-HT2A activity reduces the strength or weighting of external sensory input, shifting more processing toward internal communication and interpretation. The mechanism is proposed as a way to understand psychedelic hallucinations. Overactivation of 5-HT2A may make perception less driven by external stimuli and more internally generated, which could relate to psychiatric conditions where brain signaling balance is disrupted. The team also used computational modeling to support how circuit-level interactions reproduce the experimental effects, and suggests that receptor-targeted, low-dose approaches might eventually help restore network balance under medical supervision.