Fernando Rosas, PhD

Imperial College London

Tripping is easier with eyes closed: effects of external stimuli on brain dynamics under the psychedelic state


The Entropic Brain Hypothesis (EBH) is a simple yet powerful theory of consciousness that posits that richness of psychological experience is correlated with neural signal diversity [1]. Empirical support for EBH includes results that brain entropy (measured via Lempel-Ziv complexity, LZ [2]) decreases under anaesthesia and sleep, and increases under REM sleep, music improvisation and psychedelics. Following the EBH, we study how external stimulation affects brain dynamics and phenomenological reports under the psychedelic state. Specifically, we analysed MEG recordings and subjective experience ratings from 17 subjects under the effects of LSD and placebo in four experimental conditions: eyes closed, with and without music, and eyes open, with and without video. We find a strong interaction effect between drug and stimulus. This interaction is negative, meaning that the effect of LSD is reduced with more complex stimuli -- i.e. the effect of LSD is smaller when the subject is watching a video than when they rest with eyes closed. We also find that LZ increases with external stimuli, being lowest for eyes closed without music and highest for eyes open with video. When examining the in-scanner phenomenological reports, we observe a significant interaction effect between drug and stimulus in reported intensity of experience, positive mood, and emotional arousal. Among the four conditions, eyes closed with music was significantly above average in these three categories. As therapeutic mechanisms of psychedelics are thought to depend on their acute entropy-enhancing effects [3], these findings support the principle of closing one's eyes during a psychedelic experience.


Fernando Rosas received the B.A. degree in music composition and philosophy (Minor), the B.Sc. degree in mathematics, and the M.S. and Ph.D. degree in engineering sciences from the Pontificia Universidad Católica de Chile, Santiago, Chile, in 2003, 2007, and 2012, respectively. He worked as Postdoctoral Research Assistant with the Departement Elektrotechniek (ESAT) of KU Leuven, as Postdoctoral Fellow wih the Graduate Institute of Communication Engineering of the National Taiwan University, and as Marie Curie Reseaerch Fellow with the Department of Mathematics and the Department of Electrical and Electronic Engineering at Imperial College London. He is now a Postdoctoral Researcher at the Centre for Psychedelic Research and the Data Science Institute at Imperial College London, being also affiliated at the Centre for Complexity Science. His research interests lay in the interface between Complexity Science and Neuroscience of Consciousness.



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