Hallucinations fill the gap
Psychedelics activate a specific serotonin receptor. At least 14 different receptors are known where the neurotransmitter serotonin binds. Psychedelics have the highest affinity for the 2A receptor, which, among other effects, acts suppressive in the visual brain and also influences learning processes. “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.”
Short-term oscillations trigger communication between brain areas
In their current study, the authors show how this happens. Psychedelics intensify oscillations in visual brain areas. Generally speaking, oscillations are synchronized neural activity waves that modulate communication between brain regions. After administration of psychedelics the scientist found that visual areas produce increasingly low-frequency (5-Hz) activity waves that activate another brain region, the retrosplenial cortex. This area forms a major hub for the exchange with stored information. The brain thus switches to a new mode in which access to ongoing events is hindered and instead perceptions are increasingly generated from memory contents, “a bit like partial dreaming,” says Professor Dirk Jancke, leader of the study.
Visualizing the dynamics of brain activity in real-time
To visualize these complex processes, the scientists use an optical method that records neural activity in real-time over the entire brain surface. The mice developed by Professor Thomas Knöpfel from Hong Kong Baptist University are genetically manipulated so that they express fluorescent proteins in defined cell types. “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,” says Jancke.
Developing new therapy approaches
The results support new approaches in psychology that use psychedelics to treat, for example, anxiety disorders or depression. “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,” says Jancke.
Communications Biology
Experimental study
Animals
Psychedelic 5-HT2A Agonist Increases Spontaneous and Evoked 5-Hz Oscillations in Visual and Retrosplenial Cortex
11-Feb-2026