In short: Psilocybin, the compound in “magic mushrooms,” changes how brain regions communicate. Brain imaging studies suggest it quiets a network linked to self-focused thinking and temporarily increases communication between regions that don’t usually talk to each other. The studies are small, and researchers are still working out what this means.
From mushroom to molecule
When someone eats a psilocybin mushroom, the body converts psilocybin into psilocin. Psilocin binds to serotonin receptors, especially the 5-HT2A receptor, which is found in high concentrations in the cortex, the outer layer of the brain involved in perception, thought and mood. Serotonin is a chemical messenger. Psilocin resembles it closely enough to activate those receptors.
What brain scans have shown
One of the first modern imaging studies of psilocybin came from a research group at Imperial College London led by Robin Carhart-Harris. In a 2012 study published in PNAS, 15 healthy volunteers received psilocybin intravenously while being scanned. Researchers found decreased blood flow and activity in some central “hub” regions of the brain, including the thalamus and the anterior and posterior cingulate cortex. The drop in the medial prefrontal cortex was linked to how intense people said the experience was.
These regions are part of the default mode network, a set of areas that tends to be active when the mind wanders or reflects on itself. Reduced activity in this network under psilocybin became one of the best-known findings in the field.
Later work found a second pattern. Under psilocybin, brain regions that are usually kept separate showed more communication with each other, and overall brain activity looked less predictable. Some researchers describe this as the brain being in a more “flexible” state.
What researchers think this might mean
One idea is that psychedelics temporarily loosen the brain’s usual patterns, which may help explain the vivid changes in perception and the shifts in how people see themselves that volunteers report. Another idea is that this flexibility could make it easier for people to change entrenched patterns of thinking, which is one reason psilocybin is being studied for depression and other conditions. This is a hypothesis, not a proven mechanism.
Important limits
- Small studies. Many imaging studies, including the 2012 study above, include only a few dozen participants or fewer, mostly healthy volunteers.
- Correlation is not explanation. A change on a brain scan does not by itself explain an experience or a therapeutic effect.
- Active research. Findings are being refined, and some earlier results have been challenged or revised by larger studies.
The takeaway
Imaging research suggests psilocybin changes the way large brain networks work together, particularly the default mode network. Scientists are still early in understanding what this means for the mind and for health.
This article is for education only and is not medical advice. Psilocybin is illegal in many places, and legal status varies by country. Talk to a qualified health professional about any health decision.