Psychedelics, entropic brain theory, and the taxonomy of conscious states: a summary of debates and perspectives

Psychedelics, entropic brain theory, and the taxonomy of conscious states: a summary of debates and perspectives Sidath Rankaduwa1,2,3,* and Adrian M. Owen2,4,5,† Abstract Given their recent success in counseling and psychiatry, the dialogue around psychedelics has mainly focused on their applications for mental health. Insights from psychedelic research, however, are not limited to treating mental health, but also have much to offer our current understanding of consciousness. The investigation of psychedelic states has offered new perspectives on how different aspects of conscious experience are mediated by brain activity; as such, much more has been learned about consciousness in terms of its phenomenology and potential mechanisms. One theory that describes how psychedelics influence brain activity is the “entropic brain theory” (EBT), which attempts to understand conscious states—normal and psychedelic—in terms of “brain entropy.” Given its wide explanatory reach, this theory has several implications for current debates in consciousness research, namely the issue of whether consciousness exists in levels vs. dimensions; whether the psychedelic state is itself a “higher” level of consciousness; and if so, whether psychedelics could be used to treat disorders of consciousness. To understand how psychedelics could possibly treat a minimally conscious or vegetative patient, one must first understand EBT and how this theory intersects with these ongoing debates. Thus, this article offers a formal summary of EBT, distilling its core principles and their implications for a theoretical model of consciousness. In response to their proposed use in treating disorders of consciousness, we emphasize the importance of “set” and “setting” in ascertaining the therapeutic value of psychedelics for vegetative and/or minimally conscious patients. Keywords: disorders of consciousness; states of consciousness; entropic brain theory; psilocybin; theories and models; psychedelic states Introduction Psychedelic research has recently become a prominent field of inquiry in psychiatry, psychotherapy, neuroscience, and other disciplines. Formal investigations on classical psychedelics—such as psilocybin and lysergic acid diethylamide (LSD)—have touted a range of applications for these peculiar drugs; most impressively, perhaps, is their relevance in treating a variety of psychiatric disorders (Johnson and Griffiths 2017; Fuentes et al. 2020). For instance, various studies on psilocybin have indicated high therapeutic potential in treating a range of mental health disorders, including anxiety and depression, in both terminal cancer patients and the general population (Griffiths et al. 2016; Carhart-Harris et al. 2016a; De Gregorio et al. 2018; Johnson et al. 2019). Further research has illuminated its utility in treating addiction, with unprecedented results (Johnson et al. 2017). Setting aside their therapeutic value, the study of psychedelics has offered a variety of new perspectives for the general study of consciousness. Through these drugs, researchers have found reliable ways of safely inducing psychedelic states in both clinical and healthy populations, in hopes of better understanding their various perceptual and cognitive effects. By observing how psychedelics alter neural activity and correlating these effects with changes in conscious experience, researchers can discern how various aspects of consciousness are mediated by brain activity and how changes in specific neural systems affect conscious states (Carhart-Harris et al. 2012, 2016b). For instance, changes in the default mode network (DMN)—a network of brain regions thought to be involved in constraining and maintaining regular conscious experience (Carhart-Harris and Friston 2010)—have been associated with various perceptual shifts induced by © The Author(s) 2023. Published by Oxford University Press. This is an Open Access article distributed under the terms of the Creative Commons Attribution-NonCommercial License (https://creativecommons.org/ licenses/by-nc/4.0/), which permits non-commercial re-use, distribution, and reproduction in any medium, provided the original work is properly cited. For commercial re-use, please contact 1 Graduate Program in Neuroscience, Schulich School of Medicine & Dentistry, Western University, London, ON, Canada; 2 Western Institute for Neuroscience, Western University, London, ON, Canada; 3 Rotman Institute of Philosophy, Western University, London, ON, Canada; 4 Department of Physiology and Pharmacology, Schulich School of Medicine & Dentistry, Western University, London, ON, Canada; 5 Department of Psychology, Faculty of Social Science, Western University, London, ON, Canada † Adrian M. Owen, https://orcid.org/0000-0002-5738-3765 *Correspondence address. Department of Physiology and Pharmacology and Department of Psychology, Western University, Western Interdisciplinary Research Building, Room 6156, London, ON N6A 5B7, Canada. Fax: +519-661-3613: E-mail: 2 Rankaduwa and Owen The EBT In their initial paper, Carhart-Harris et al. (2014) put forth their EBT by weaving together findings from various brain imaging and neuropharmacological studies, which have all investigated psychedelic drugs and their effects on brain communication (within and between specific brain networks). These processes are believed to be involved in maintaining our day-to-day conscious experience. EBT attempts to understand psychedelic states in terms of their underlying neural changes—more specifically, how they rank in terms of brain entropy. By “entropy,” the authors essentially mean “disorder” or “randomness.” To say that conscious states are a function of brain entropy is to say that the level of entropy (or disordered activity) in the brain can serve as an index for one’s “level” of conscious experience. In exploring this view, EBT addresses entropy as it applies to normal waking consciousness and contrasts this with how entropy differs in the psychedelic state. From this comparison, Carhart-Harris et al. (2014) distinguish two kinds of conscious states: “primary states,” which are conscious states that most closely resemble (but are not limited to) the psychedelic experience, and “secondary states,” which are more akin to experiences in normal waking consciousness. It is worth mentioning here that the terms “primary” and “secondary” are borrowed from the psychoanalytic theory of Freud, who elaborated concepts of primary and secondary processes within the human psyche. Freud is perhaps most well known for his concepts of the “ego” and the “id” as competing processes within an individual: the id is the primary process that represents the “primitive” aspects of a person, driven by instinctual desires and tendencies; the ego is the secondary process that uses reason to negotiate these desires, representing the part of the individual that has been shaped by culture. Although these concepts refer strictly to (...truncated)