Research library / Brain imaging study
Neural correlates of the psychedelic state as determined by fMRI studies with psilocybin
Carhart-Harris RL, Erritzoe D, Williams T, et al. Proceedings of the National Academy of Sciences of the United States of America 2012;109(6):2138-43
Researchers scanned 30 healthy volunteers while they received intravenous psilocybin or placebo, to see how the brain changes as the psychedelic state begins. Half were scanned with a method measuring blood flow and half with standard fMRI. Contrary to the team's expectation, psilocybin only reduced activity, and the largest drops were in major connecting hubs such as the thalamus and the cingulate cortex. The bigger the drop in a frontal region, the stronger people rated the drug's effects. Psilocybin also loosened the normal link between two core parts of the brain's default mode network. The authors suggest psychedelic effects come from reduced activity in these hubs. This is a short-term imaging study in healthy people and does not test therapeutic use.
What it found
- Psilocybin produced only decreases in cerebral blood flow and BOLD signal, largest in hub regions such as the thalamus and anterior and posterior cingulate cortex
- Reduced activity in the anterior cingulate and medial prefrontal cortex predicted how intense the subjective effects were
- Psilocybin significantly weakened coupling between the medial prefrontal cortex and posterior cingulate cortex