Scientists Map How Psychedelics Shift Vision from External Input to Memory
Psychedelic substances affect the brain by binding to serotonin receptors. Scientists have identified at least 14 receptors that respond to serotonin, but psychedelics psychedelics bind strongly to one called the 2A receptor. This receptor influences learning and also reduces activity in parts of the brain responsible for processing visual information.
“We have observed in earlier studies that visual processes in the brain are suppressed by this receptor,” says Callum White, the study’s first author. “This means that visual information about things happening in the outside world becomes less accessible to our consciousness. To compensate for this gap, our brain inserts fragments from memory — it hallucinates.”
In practical terms, when incoming visual signals are weakened, the brain compensates by drawing on stored images and experiences. Those internally generated fragments can blend with perception, producing hallucinations.
Slow Brain Waves Shift Perception Toward Memory
The researchers also examined how this shift develops moment by moment. They found that psychedelics increase rhythmic patterns of brain activity known as oscillations in visual regions. Oscillations are coordinated waves of neural firing that help different brain areas communicate.
After psychedelics were administered, the researchers observed an increase in low-frequency waves (around 5 Hz) in visual areas. These slower waves activated the retrosplenial cortex, a key hub involved in accessing stored memories. As communication between these regions strengthens, the brain appears to switch into a different operating mode: awareness of what is happening externally becomes weaker, while perception relies more heavily on recalled information. Professor Dirk Jancke, who led the study, describes the effect as “a bit like partial dreaming.”
Real-Time Brain Imaging Reveals the Mechanism
To capture these changes, the scientists used an optical imaging technique that monitors neural activity across the brain’s surface in real time. The experiments were carried out in specially engineered mice developed by Professor Thomas Knöpfel at Hong Kong Baptist University. These animals were designed to produce fluorescent proteins in specific brain cells, allowing researchers to track activity with high precision.
This method made it possible to identify the origin of the recorded signals. “We therefore know exactly in our experiments that the measured fluorescent signals originate from pyramidal cells of the cortical layers 2/3 and 5, which mediate communication within and between brain regions,” Jancke says. These cells are crucial for transmitting information across the cortex.
Implications for Depression and Anxiety Treatment
The findings may also help researchers improve psychedelic-assisted therapy. Under medical supervision, these substances may temporarily shift brain activity in ways that promote access to positive memories and weaken deeply ingrained negative thought patterns.
“When used under medical supervision, such substances can temporarily change the state of the brain to selectively recall positive memory content and restructure learned, excessively negative thought patterns, i.e., to be able to unlearn negative context. It will be exciting to see how such therapies are further personalized in the future,” Jancke says.
By showing how psychedelics can redirect perception away from real-time sensory input and toward internal memory networks, the study offers a clearer biological explanation for hallucinations and for why these compounds may have therapeutic potential.
