Neural correlates of the psychedelic state as determined by fMRI studies with psilocybin
π Original studyPlain English Summary
Here's a result that surprised almost everyone: when researchers gave volunteers psilocybin (the active ingredient in magic mushrooms) and watched their brains in a scanner, brain activity went down, not up. Every single region showed decreases β not a single area lit up more. The biggest drops hit the same default mode network hubs that quiet down during meditation β the thalamus, the cingulate cortex, and the medial prefrontal cortex. Even more telling, the stronger someone's brain activity dropped in one key region, the more intense their psychedelic experience felt. The connections between major DMN hubs also loosened up significantly. The researchers argue this supports a beautifully old idea from Aldous Huxley: that the brain normally acts as a "reducing valve," filtering the flood of possible consciousness down to a manageable trickle, and psychedelics work by opening that valve wider. This finding created a fascinating bridge to meditation research β both practices seem to quiet the brain's bossy default network, potentially unlocking less constrained ways of thinking. The paper became a landmark in psychedelic neuroscience and remains central to debates about whether consciousness might be broader than our everyday brain filtering allows.
Abstract
Psychedelic drugs have a long history of use in healing ceremonies, but despite renewed interest in their therapeutic potential, we continue to know very little about how they work in the brain. Here we used psilocybin, a classic psychedelic found in magic mushrooms, and a task-free functional MRI (fMRI) protocol designed to capture the transition from normal waking consciousness to the psychedelic state. Arterial spin labeling perfusion and blood-oxygen level-dependent (BOLD) fMRI were used to map cerebral blood ο¬ow and changes in venous oxygenation before and after intravenous infusions of placebo and psilocybin. Fifteen healthy volunteers were scanned with arterial spin labeling and a separate 15 with BOLD. As predicted, profound changes in consciousness were observed after psilocybin, but surprisingly, only decreases in cerebral blood ο¬ow and BOLD signal were seen, and these were maximal in hub regions, such as the thalamus and anterior and posterior cingulate cortex (ACC and PCC). Decreased activity in the ACC/medial prefrontal cortex (mPFC) was a consistent ο¬nding and the magnitude of this decrease predicted the intensity of the subjective effects. Based on these results, a seed-based pharmaco-physiological interaction/functional connectivity analysis was performed using a medial prefrontal seed. Psilocybin caused a signiο¬cant decrease in the positive coupling between the mPFC and PCC. These results strongly imply that the subjective effects of psychedelic drugs are caused by decreased activity and connectivity in the brain's key connector hubs, enabling a state of unconstrained cognition.
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π Cite this paper
Carhart-Harris, Robin L, Erritzoe, David, Williams, Tim, Stone, James M, Reed, Laurence J, Colasanti, Alessandro, Tyacke, Robin J, Leech, Robert, Malizia, Andrea L, Murphy, Kevin, Hobden, Peter, Evans, John, Feilding, Amanda, Wise, Richard G, Nutt, David J (2012). Neural correlates of the psychedelic state as determined by fMRI studies with psilocybin. Proceedings of the National Academy of Sciences. https://doi.org/10.1073/pnas.1119598109
@article{carhart_harris_2012_psilocybin_neural,
title = {Neural correlates of the psychedelic state as determined by fMRI studies with psilocybin},
author = {Carhart-Harris, Robin L and Erritzoe, David and Williams, Tim and Stone, James M and Reed, Laurence J and Colasanti, Alessandro and Tyacke, Robin J and Leech, Robert and Malizia, Andrea L and Murphy, Kevin and Hobden, Peter and Evans, John and Feilding, Amanda and Wise, Richard G and Nutt, David J},
year = {2012},
journal = {Proceedings of the National Academy of Sciences},
doi = {10.1073/pnas.1119598109},
}