Neural correlates of the psychedelic state as determined by fMRI studies with psilocybin
Proceedings of the National Academy of Sciences – January 23, 2012
Source: OpenAlex
Summary
Psilocybin, a psychedelic compound from magic mushrooms, significantly alters consciousness by decreasing cerebral blood flow and brain activity, particularly in key regions like the anterior and posterior cingulate cortex (ACC and PCC). In a study with 30 healthy volunteers, those receiving psilocybin exhibited reduced connectivity between the medial prefrontal cortex (mPFC) and PCC. Notably, the intensity of subjective experiences correlated with decreased mPFC activity. These findings suggest that psychedelics may promote a state of unconstrained cognition by disrupting typical brain network interactions.
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 flow 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 flow 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 finding 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 significant 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.