The use of Psilocybin in scientific and experimental clinical contexts has triggered renewed interest in the mechanism of action of psychedelics. However, its time-dependent systems-level neurobiology remains sparsely investigated in humans.
We therefore conducted a double-blind, randomized, counterbalanced, cross-over study during which 23 healthy human participants received placebo and 0.2 mg/kg of psilocybin p.o. on two different test days. Participants underwent MRI scanning at three time points between administration and peak effects: 20 mins, 40 mins, and 70 mins after administration. Resting-state functional connectivity was quantified via a data-driven global brain connectivity method and compared to cortical gene expression maps.
Psilocybin reduced associative, but concurrently increased sensory brain-wide connectivity. This pattern emerged over time from administration to peak-effects. Furthermore, we show that baseline connectivity is associated with the extent of Psilocybin-induced changes in functional connectivity. Lastly, Psilocybin induced changes correlated time-dependently with spatial gene expression patterns of the 5-HTR2A and 5-HTR1A.
These results suggest that the integration of functional connectivity in sensory and the disintegration in associative regions may underlie the psychedelic state and pinpoint the critical role of the serotonin 2A and 1A receptor systems. Furthermore, baseline connectivity may represent a predictive marker of the magnitude of changes induced by psilocybin and may therefore contribute to a personalized medicine approach within the potential framework of psychedelic treatment.