Shannon entropy of brain functional complex networks under the influence of the psychedelic Ayahuasca

The entropic brain hypothesis suggests that psychedelic experiences arise from increased randomness in the brain's functional connectivity. Analyzing resting-state fMRI data from human subjects before and after ingesting ayahuasca, a psychedelic beverage used in Amazonian religious and scientific contexts, researchers found that the Shannon entropy of the brain's degree distribution increased, indicating greater disorder in network connections. Local integration within brain networks increased while global integration decreased. These findings align with the entropic brain hypothesis and relate to users' reports of 'mind-expansion.'

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Abstract

The entropic brain hypothesis holds that the key facts concerning psychedelics are partially explained in terms of increased entropy of the brain's functional connectivity. Ayahuasca is a psychedelic beverage of Amazonian indigenous origin with legal status in Brazil in religious and scientific settings. In this context, we use tools and concepts from the theory of complex networks to analyze resting state fMRI data of the brains of human subjects under two distinct conditions: (i) under ordinary waking state and (ii) in an altered state of consciousness induced by ingestion of Ayahuasca. We report an increase in the Shannon entropy of the degree distribution of the networks subsequent to Ayahuasca ingestion. We also find increased local and decreased global network integration. Our results are broadly consistent with the entropic brain hypothesis. Finally, we discuss our findings in the context of descriptions of "mind-expansion" frequently seen in self-reports of users of psychedelic drugs.