Inside The Expanded Mind: The Science Behind Psychedelic Effects

What really happens in your brain during a psychedelic experience? A global study has gathered data from several countries and is finally beginning to reveal how these substances reorganize the mind, and why this could revolutionize the treatment of mental illnesses.

Scientific interest in psychedelics has returned strongly in recent decades, especially for their potential in treating mental disorders such as depression, anxiety, and chemical dependency. These substances, such as psilocybin, LSD, and DMT, produce profound changes in perception, emotions, and the way we think.

Despite this evident impact on conscious experience, for a long time scientists did not know exactly what happened in the brain during these altered states. The study in question arises precisely to answer this question: how do psychedelics reorganize brain activity?

To understand this, researchers focused on a technique called resting-state functional magnetic resonance imaging (fMRI). This examination allows them to observe how different regions of the brain "talk" to each other even when the person is not performing any specific task.

Instead of looking at an isolated area, scientists analyze entire brain communication networks, assessing how synchronized these regions are over time. This type of analysis is essential for understanding complex phenomena such as consciousness and perception.

One of the major problems in the field was that previous studies were small and often presented contradictory results. Different laboratories used varied methods, analyzed few participants, and therefore reached conclusions that did not always coincide.

To overcome this limitation, the researchers decided to do something more ambitious: to combine data from several studies around the world into a single analysis. This type of approach is called a mega-analysis.

In total, they gathered data from 11 different studies, conducted in five countries and three continents, involving hundreds of brain scans. This data included people under the influence of different psychedelics, such as psilocybin, LSD, mescaline, and DMT. A crucial step was to standardize all the processing of this information. In other words, they applied the same analytical “treatment” to all the data, ensuring that the comparisons were fair and consistent.

After this standardization, the scientists analyzed how the connectivity between brain regions changed under the influence of these substances. They also used a more sophisticated statistical model, called the Bayesian approach.

Instead of simply stating whether an effect exists or not, this model allows for estimating the degree of confidence in the results. This helps to better deal with uncertainties and variations between studies, offering a more realistic view of what is happening in the brain.

The results showed a rather interesting pattern. Under the influence of psychedelics, brain regions that normally function more independently begin to communicate more with each other. It's as if barriers between different brain "networks" are temporarily reduced.

At the same time, some internal connections within these networks decrease. This rearrangement may explain why people report unusual experiences, such as freer thinking, greater association of ideas, and changes in self-perception.

Furthermore, deeper areas of the brain, responsible for emotions and sensory processing, also showed significant changes. This suggests that psychedelics affect not only abstract thought but also systems linked to bodily sensation and emotions.

Taken together, these effects indicate that the brain enters a more flexible and less rigid state, which may be related to both intense subjective experiences and potential therapeutic benefits.

Overall, this study represents an important advance because it managed to unite different research into a clearer and more consistent view. By overcoming the limitations of isolated studies, it offers a more reliable "map" of how psychedelics alter brain function. This type of knowledge is essential for developing safer, more effective, and personalized treatments in the future.

READ MORE:

An international mega-analysis of psychedelic drug effects on brain circuit function

Manesh Girn, Manoj K. Doss, Leor Roseman, Katrin H. Preller, Fernanda Palhano-Fontes, Lorenzo Pasquini, Frederick S. Barrett, Pablo Mallaroni, Natasha L. Mason, Christopher Timmermann, Drummond E. McCulloch, Patrick M. Fisher, Brian S. Winston, Flora Moujaes, Felix Muller, Matthias E. Liechti, Franz X. Vollenweider, Johannes G. Ramaekers, Kim Kuypers, Draulio B. Araujo, Olaf Sporns, Joshua Siegel, Nico Dosenbach, David J. Nutt, Robin L. Carhart-Harris, Emmanuel A. Stamatakis, and Danilo Bzdok. 

Nature Medicine. 06 April 2026

DOI:10.1038/s41591-026-04287-9

Abstract:

Psychedelic drugs are re-emerging as promising scientific and clinical tools. However, despite a rapidly expanding literature on their therapeutic value, the neural mechanisms underlying psychedelic effects remain unclear. Resting-state functional magnetic resonance imaging studies of acute psychedelic effects, conducted independently by several research groups, have so far yielded fragmented and sometimes inconsistent findings. Here, to help facilitate greater convergence, we conducted a ‘mega-analysis’ integrating 11 independent resting-state functional magnetic resonance imaging datasets across five psychedelic drugs (psilocybin, lysergic acid diethylamide, mescaline, N,N-dimethyltryptamine and ayahuasca) from research groups spanning three continents and five countries. By applying a uniform preprocessing pipeline and a Bayesian hierarchical modeling framework, we discovered several common features in the induced alterations to brain function across drugs and sites. Most prominently, we identified a core signature of increased functional connectivity between transmodal (default, frontoparietal and limbic) and unimodal networks (visual and somatomotor), with subnetwork specificity. Furthermore, key subcortical regions (thalamus, caudate and putamen) and the cerebellum exhibited altered coupling with sensorimotor networks. In contrast to several single-site reports, Bayesian modeling revealed weak-to-moderate and selective reductions in within-network functional connectivity, with substantial variability across drugs and networks. Together, these findings extend past work by demonstrating that psychedelics reconfigure large-scale cortical organization while selectively engaging subcortical circuitry. This study provides the most comprehensive synthesis of psychedelic brain action to date, helping resolve inconsistencies and offering a probabilistic map of how psychedelics alter large-scale brain organization. We hereby provide a cornerstone to benchmark and shepherd future psychedelic neuroimaging research.