For decades, people using psychedelics have described a feeling where the line between ‘me’ and the world vanishes. While it is clear these drugs cause intense shifts in vision and thought, scientists have struggled to pin down exactly what the brain is doing.
A new multi-centric study published in Nature Medicine on April 6 has suggested the answer isn’t found in a single centre such as the thalamus or amygdala but that it arises from a total reorganisation of how different brain areas talk to one another.
To find a reliable pattern, researchers from Canada, the U.K., and the U.S. pooled 11 global datasets into a library of 500 fMRI scans — images that track changes in blood flow to show which parts of the brain are working. This included 267 people under the influence of LSD, psilocybin, DMT, mescaline or ayahuasca.
Previously, labs used software to clean data skewed by factors such as head moving during scanning, often producing contradictory results. To fix this, the team took the raw data and ran them through a single, common processing system to ensure they were comparing apples to apples for the first time.
Chain of command
The team had to figure out which brain changes were caused by the drugs and which were arbitrary differences between people or MRI machines. Instead of the usual statistical methods, the team used Bayesian modelling. It works like a fair judge who doesn’t simply declare guilty or innocent: it says exactly how confident it is and automatically prefers results based on hundreds of volunteers than those based on a handful. This let the researchers filter out the quirks and focus on the brain patterns that reliably appeared across every drug and lab.
University of Ottawa neuroscientist Sergio Perez-Rosal said “moving away from overconfident ‘yes’ or ‘no’ claims towards a more nuanced, uncertainty-aware conclusion represents a rare kind of epistemic humility” — meaning the scientific honesty to admit exactly what we don’t know, especially in the fledgling field of consciousness studies.
To understand the findings, it helps to see the brain as a building with a strict chain of command. In our normal, everyday state, the brain has a hierarchy. At the bottom are frontline workers, the brain regions that handle raw sensory input. At the top are the high-level managers — the parts of the brain responsible for abstract thought, memory, and our internal sense of self. Usually, these two groups don’t talk to each other directly. They are separated by layers of filters that keep our raw senses from overwhelming our complex thoughts.
‘Change how information flows’
The analysis found that psychedelics essentially collapse this ladder, instead increasing cross-talk, i.e. the thinking regions and the sensory regions begin exchanging information directly. And this collapses the neural boundary that usually defines ‘you’ as distinct from the world.
“What surprised us most is that psychedelics don’t just affect specific spots, they change how information flows across the entire brain,” Manesh Girn, a neuroscientist at the University of California San Francisco, and first author of the study, said. “The usual hierarchy between ‘high-level’ thought and ‘bottom-up’ perception starts to dissolve. Inner and outer experience begin to blur.”
While in a normal state, the brain operates like a city of segregated neighborhoods, where signals stay in their own lanes and travel only along established routes, psychedelics dissolve these boundaries. Dr. Girn said this is best described as a city where new, direct highways suddenly open up.
“This connects neighborhoods that usually you have to move through multiple smaller neighborhoods to get to,” he said. “Now, you can get from A to C without needing to go through B.”
Out of ruts
While the study offered the most robust map to date of the brain under psychedelics, Michiel van Elk, a cognitive psychologist at Leiden University said scientists must look closer at the tools used to draw it. He said psychedelics act on serotonin receptors, which naturally regulate the tension of blood vessels. Since fMRI tracks blood flow to guess where the brain is active, a drug that changes vessel tension could create a measurement artifact. Without using other techniques beyond fMRI, he argued, it remains unclear if these new highways are a reliable signature of neuronal firing or simply a side effect of how the drugs affect our blood.
Beyond the laboratory, in clinics, where psychedelics have been gaining traction as a therapeutic intervention, this study provides a vital biological clue for why these drugs might work as medicine. Akanksha Dadlani, a psychiatrist at Stanford University, said the flattened hierarchy found in the scans could explain how psychedelics “loosen the rigid patterns of thought” seen in depression.
“By temporarily breaking down the brain’s strict chain of command, the drugs may allow patients to step out of long-held mental ruts.”
‘Powerful tool’
However, Dr. Dadlani and Prof. Perez-Rosal both cautioned that a change in wiring is only a catalyst, not a magic bullet. The drug may physically open a door by rewiring the brain’s shortcuts. Prof. Perez-Rosal added that the actual healing will depend on how that experience is integrated into the patient’s life afterwards.
Matthew Wall, a neuroscientist and imaging expert at Imperial College London, said the real advance is that by unifying the most data to date, the study has established new baselines for how psychedelics trigger cross-talk. While the study used healthy volunteers, Dr. Wall said, “identifying this clear neural signature provides a solid foundation for understanding how psychedelic treatments may work in clinical practice.”
Ultimately, the study offers something more subtle than clinical promise: a rare glimpse into the mechanics of human awareness. For Dr. Girn, the work shows how psychedelics can be a “powerful perturbational tool” to break down the fundamental structures of experience, letting researchers understand how they are usually maintained.
Anirban Mukhopadhyay is a geneticist by training and science communicator from New Delhi.
Published – May 11, 2026 07:30 am IST
