• Joan Francesc Alonso, Sergio Romero, Miquel Àngel Mañanas, and Jordi Riba.
• Biomedical Engineering Research Centre, Department of Automatic Control (Drs Alonso, Romero, and Mañanas), and Barcelona College of Industrial Engineering (Drs Alonso and Mañanas), Universitat Politècnica de Catalunya, Barcelona, Spain; CIBER de Bioingeniería, Biomateriales y Nanomedicina, Spain (Drs Romero and Mañanas); Human Neuropsychopharmacology Group, Sant Pau Institute of Biomedical Research, Barcelona, Spain (Dr Riba); Department of Pharmacology and Therapeutics, Universitat Autònoma de Barcelona, Barcelona, Spain (Dr Riba); Centro de Investigación Biomédica en Red de Salud Mental, CIBERSAM, Spain (Dr Riba).
• Int. J. Neuropsychopharmacol. 2015 Mar 28; 18 (8).

BackgroundPsychedelics induce intense modifications in the sensorium, the sense of "self," and the experience of reality. Despite advances in our understanding of the molecular and cellular level mechanisms of these drugs, knowledge of their actions on global brain dynamics is still incomplete. Recent imaging studies have found changes in functional coupling between frontal and parietal brain structures, suggesting a modification in information flow between brain regions during acute effects.MethodsHere we assessed the psychedelic-induced changes in directionality of information flow during the acute effects of a psychedelic in humans. We measured modifications in connectivity of brain oscillations using transfer entropy, a nonlinear measure of directed functional connectivity based on information theory. Ten healthy male volunteers with prior experience with psychedelics participated in 2 experimental sessions. They received a placebo or a dose of ayahuasca, a psychedelic preparation containing the serotonergic 5-HT2A agonist N,N-dimethyltryptamine.ResultsThe analysis showed significant changes in the coupling of brain oscillations between anterior and posterior recording sites. Transfer entropy analysis showed that frontal sources decreased their influence over central, parietal, and occipital sites. Conversely, sources in posterior locations increased their influence over signals measured at anterior locations. Exploratory correlations found that anterior-to-posterior transfer entropy decreases were correlated with the intensity of subjective effects, while the imbalance between anterior-to-posterior and posterior-to-anterior transfer entropy correlated with the degree of incapacitation experienced.ConclusionsThese results suggest that psychedelics induce a temporary disruption of neural hierarchies by reducing top-down control and increasing bottom-up information transfer in the human brain.© The Author 2015. Published by Oxford University Press on behalf of CINP.

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