Sackler Centre for Consciousness Science

Neural correlates of the psychedelic state

In a recent study we analysed state-of-the-art new magnetoencephalography (MEG) recordings from healthy volunteers who had received LSD, ketamine or psilocybin, a compound found in magic mushrooms. We found increased neural dynamical complexity during the psychedelic state, as measured by the Lempel-Ziv index. The complexity index captures the degree of randomness and diversity of patterns in the data and correlates with the more “fluid” phenomenology experienced in the psychedelic state. The finding is interesting because it is the first demonstration that there exists a brain state with higher complexity than the wakeful resting state. In parallel research (see Theory and Modelling) we are studying in detail the decreases in complexity observed during anaesthesia and non-rapid eye movement sleep.

Professor Anil Seth: “What we find is that under each of these psychedelic compounds, this specific measure of global conscious level goes up, so it moves in the other direction. The neural activity becomes more unpredictable”. “Until now, we’ve only ever seen decreases compared to the baseline of the normal waking state.”

We are also analysing functional connectivity, including Granger causality on these data, and exploring the correlation of multiple neural dynamical features with individual reports of altered experience. In this way we aim to further enhance our understanding of the neurophysiological, cognitive and experiential changes underlying the psychedelic state. There is also potential clinical application for these psychoactive substances, as they are currently being trialled as treatment for depression and anxiety.


Michael Schartner, Adam Barrett, Lionel Barnett, Anil Seth (in collaboration with Robin Carhart-Harris, Imperial College London and Suresh Muthukumaraswamy, University of Auckland, New Zealand)

Related Publications:

Schartner, M.M., Carhart-Harris, R.L., Barrett, A.B., Seth, A.K., Muthukumaraswamy, S.D.(2017) Increased spontaneous MEG signal diversity for psychoactivef ketamine, LSD and psilocybin.Scientific Reports 7: 46421

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