Scientists have demonstrated, for the first time, that several psychedelic drugs - including psilocybin, LSD, mescaline, DMT and ayahuasca - produce a common pattern of brain activity despite their distinct chemistries.
An international consortium led by a McGill University researcher pooled brain imaging data from labs across five countries, creating the largest study of its kind to date.
The findings, published in Nature Medicine, could help guide the design of future treatments for mental health disorders.
"This is a breakthrough in how we think about psychedelic drugs," said senior author Danilo Bzdok, Associate Professor in McGill's Department of Biomedical Engineering and Canada CIFAR Artificial Intelligence Chair at Mila. "For the first time, we show there's a common denominator among drugs that we currently consider completely separate."
Two measurable changes in the brain
While different psychedelics have shown benefits for some mental health conditions, how they produce similar effects despite their chemical differences remains a mystery. The meta-analysis identified two consistent neural effects across five of the most common drugs.
Normally, each brain system communicates strongly within itself, maintaining tight, organized networks. The researchers found that under the influence of psychedelics, these connections weaken, making the networks less rigidly structured.
The second neural effect is that psychedelics increase communication between different brain networks, allowing signals to cross boundaries that are usually separate. This "cross-talk" may help explain the hallucinations and other unusual thoughts, sensations and perceptions people report during psychedelic experiences.
An 'X-ray' of global psychedelic research
The meta-analysis combined results from 11 datasets, analyzing more than 500 brain imaging sessions from 267 participants.
Psychedelic neuroscience studies are typically small, often limited to 10 to 30 participants because of high costs and strict regulations. Studying five different psychedelics in a single experiment would be nearly impossible, the authors note.
"This approach gives us an X-ray view of the entire research community," said Bzdok.
The thawing of 'psychedelic research winter'
Interest in psychedelics for mental health treatment has surged in recent years, fuelled in part by advances in brain imaging technologies. The revival follows what authors call the "psychedelic research winter" of the 1970s, when studies were limited by criminalization and associations with counterculture.
"Many drug therapies for depression, for example, have changed little over the past decades. Psychedelics may represent the most promising shift in mental health treatment since the 1980s," said Bzdok.
He added that, as researchers in this emerging field still face logistical hurdles, the results provide a yardstick against which future studies can be measured and may help move the needle toward loosening strict regulations.
About the study
"An international mega-analysis of psychedelic drug effects on brain circuit function" by Manesh Girn and Danilo Bzdok et al., was published in Nature Medicine.
