Study links psychedelics to reduced visual input and increased memory-driven perception
Scientists reported that psychedelics dampen visual processing and increase 5-Hz brain waves linked to memory recall. Real-time imaging in mice showed perception shifting from external input toward internally stored images.
Psychedelic substances act on the brain by binding to serotonin receptors, and scientists reported that psychedelics are especially drawn to the 2A receptor, which not only affects learning but also dampens activity in parts of the brain responsible for processing visual information. Researchers said psychedelics can quiet the brain’s visual input system, pushing it to replace missing details with vivid fragments from memory, and that slow, rhythmic brain waves help shift perception away from the outside world and toward internal recall.
"We have observed in earlier studies that visual processes in the brain are suppressed by this receptor," the study said. "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." In other words, when incoming visual signals are reduced, the brain compensates by pulling stored images and experiences from memory, and those internally generated fragments can blend into perception, producing hallucinations.
The researchers said psychedelics increase rhythmic patterns of brain activity, known as oscillations, in visual regions. After psychedelics were administered, the team observed a rise in low-frequency (5-Hz) waves in visual areas. These slower waves stimulated the retrosplenial cortex, a key hub involved in accessing stored memories, and as this communication strengthens, awareness of current external events becomes weaker while perception relies more heavily on recalled information.
To capture these changes, the scientists used an advanced optical imaging technique that tracks neural activity across the entire surface of the brain in real time. The experiments relied on specially engineered mice designed to produce fluorescent proteins in specific types of brain cells. The researchers said the measured fluorescent signals originate from pyramidal cells of the cortical layers 2/3 and 5, which mediate communication within and between brain regions.
The findings may also help refine psychedelic-assisted therapy. Researchers said that, under medical supervision, these substances can temporarily shift brain activity in ways that encourage the recall of positive memories and weaken deeply ingrained negative thought patterns. The study was published in Communications Biology as "Psychedelic 5-HT2A agonist increases spontaneous and evoked 5-Hz oscillations in visual and retrosplenial cortex."