Enhanced repertoire of brain dynamical states during the psychedelic experience

TL;DR

This study investigates how psilocybin alters brain dynamics and connectivity, revealing increased variability and a broader range of connectivity states, which may explain the unconstrained consciousness experienced during the psychedelic state.

Contribution

The paper introduces a novel framework to track brain connectivity states, demonstrating increased repertoire of states during psilocybin-induced altered consciousness.

Findings

Increased BOLD signal variability in hippocampi and anterior cingulate cortex.

Alterations in spectral behavior in default mode, executive control, and dorsal attention networks.

Wider repertoire of connectivity states post-psilocybin.

Abstract

The study of rapid changes in brain dynamics and functional connectivity (FC) is of increasing interest in neuroimaging. Brain states departing from normal waking consciousness are expected to be accompanied by alterations in the aforementioned dynamics. In particular, the psychedelic experience produced by psilocybin (a substance found in `magic mushrooms`) is characterized by unconstrained cognition and profound alterations in the perception of time, space and selfhood. Considering the spontaneous and subjective manifestation of these effects, we hypothesize that neural correlates of the psychedelic experience can be found in the dynamics and variability of spontaneous brain activity fluctuations and connectivity, measurable with functional Magnetic Resonance Imaging (fMRI). Fifteen healthy subjects were scanned before, during and after intravenous infusion of psilocybin and an inert placebo. Blood-Oxygen Level Dependent (BOLD) temporal variability was assessed computing the variance and total spectral power, resulting in increased signal variability bilaterally in the hippocampi and anterior cingulate cortex. Changes in BOLD signal spectral behavior (including spectral scaling exponents) affected exclusively higher brain systems such as the default mode, executive control and dorsal attention networks. A novel framework enabled us to track different connectivity states explored by the brain during rest. This approach revealed a wider repertoire of connectivity states post-psilocybin than during control conditions. Together, the present results provide a comprehensive account of the effects of psilocybin on dynamical behaviour in the human brain at a macroscopic level and may have implications for our understanding of the unconstrained, hyper-associative quality of consciousness in the psychedelic state.