Different psychedelics appear to produce a shared pattern of changes in how brain regions communicate.
Psychedelic drugs are drawing renewed interest as possible tools for mental health treatment, but researchers still do not fully understand how they affect the brain. To tackle that question, scientists combined brain-scan data from several countries and analyzed them together to see whether different drugs produce similar changes in the brain.
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The researchers carried out a mega-analysis, meaning they pooled individual brain-scan data from multiple earlier studies and reanalyzed them together. They focused on resting-state functional magnetic resonance imaging, or resting-state fMRI, which tracks how strongly activity in different brain regions rises and falls together while a person is lying still and not performing a task. The final analysis included 519 usable scans from 267 healthy adults across 11 datasets, most of which compared a psychedelic condition with a matched placebo condition. The drugs studied were psilocybin, lysergic acid diethylamide (LSD), mescaline, N,N-dimethyltryptamine (DMT), and ayahuasca.
- Across these drugs, the clearest overall pattern was that certain groups of brain areas that usually work more independently became more connected. At the same time, activity within some networks became a bit less in sync.
- Brain networks involved in higher-level functions such as self-related thought, flexible thinking, and staying focused on goals became more strongly linked with networks that process sight and body movement. This was the most consistent shared effect across the full dataset.
- Some deeper brain areas that help connect perception with action also showed consistent changes.
- The results did not support a simple idea that psychedelics cause a broad breakdown of brain organization. Instead, the effects were more selective, with small reductions mainly seen in networks involved in sight and body movement, rather than across the whole brain.
- Psilocybin and LSD showed very similar brain patterns, and mescaline largely followed the same trend. DMT appeared to produce stronger changes, but the results were less certain because the dataset was small and more variable. Ayahuasca showed a more unusual pattern than the other drugs.
Taken together, the findings suggest that psychedelics make the brain's usual organization less rigid. Normally, systems that handle basic input, like vision and movement, stay more separate from those involved in complex thinking. Under these drugs, those boundaries become less clear, and some brain systems interact more than they normally do. The study also found consistent changes in deeper brain regions that help turn perception into action, suggesting that psychedelics may alter how the brain links what we experience to how we respond.
The combined datasets differed in scanner type, psychedelic dose, route of administration, and the timing of the scan after drug use. Even with those limitations, this study provides one of the clearest pictures so far of how different psychedelics change communication across the brain. In episode #30, Dr. Roland Griffiths discusses the effects of the psychedelic compound psilocybin on the human brain.