Who Is Robin Carhart-Harris

Robin Carhart-Harris is a British neuroscientist and psychologist who has become one of the most prominent and influential psychedelic researchers of the twenty-first century. Trained at Bournemouth University, Brunel University, and the University of Bristol, he completed his PhD in psychopharmacology at Bristol before joining Imperial College London, where he founded and directed the Centre for Psychedelic Research—the first academic center dedicated to psychedelic research in a major university. In 2021, he moved to the University of California, San Francisco, to direct the Neuroscape Psychedelics Division. His work combines functional neuroimaging (fMRI), clinical trials, and theoretical neuroscience to investigate how psychedelics alter brain function and why these alterations can produce lasting therapeutic benefits.

Carhart-Harris’s relevance to IMHU’s mission is both scientific and theoretical. His brain-imaging studies have produced some of the most important empirical findings in the field: showing that psychedelics reduce activity in the brain’s default mode network (DMN)—the neural circuitry associated with self-referential thinking and the sense of a stable ego—and that they increase connectivity between brain regions that don’t normally communicate. These findings provide a neurobiological basis for the subjective experience of ego dissolution, expanded awareness, and novel perception that psychedelic users report. His "entropic brain hypothesis" offers a theoretical framework for understanding these effects: psychedelics increase the entropy (disorder, flexibility) of brain activity, temporarily disrupting rigid patterns and allowing the system to reorganize in potentially healthier configurations. This theory has become one of the most widely discussed models in consciousness research.

Core Concepts

1. The default mode network (DMN) and ego dissolution: Carhart-Harris’s early imaging studies showed that psilocybin and LSD decrease activity in the DMN—a network of brain regions active during self-referential thought, mind-wandering, and narrative self-construction. The degree of DMN suppression correlated with the intensity of reported ego dissolution. This finding provided a neural correlate for what meditators and mystics have described for millennia: the experience of the self dropping away. It also suggested a mechanism for therapeutic change: by temporarily quieting the brain’s self-referential machinery, psychedelics may allow people to step outside rigid patterns of self-related thinking—including the ruminative loops characteristic of depression and anxiety.
2. The entropic brain hypothesis: Carhart-Harris proposed that psychedelics increase the entropy (informational complexity and randomness) of brain activity. In normal waking consciousness, the brain operates in a relatively constrained, ordered state; under psychedelics, this order loosens, allowing greater flexibility, novel connections, and access to a wider range of mental states. He suggested that both ends of the entropy spectrum can be pathological: too little entropy produces rigid, repetitive mental states (depression, addiction, OCD), while too much produces chaotic, disorganized states (psychosis). Psychedelics may be therapeutic precisely because they temporarily increase entropy in people whose brain activity has become pathologically rigid.
3. The REBUS model (Relaxed Beliefs Under Psychedelics): Building on the entropic brain hypothesis, Carhart-Harris and Karl Friston proposed that psychedelics work by "relaxing" the brain’s high-level predictive models—the prior beliefs and assumptions that normally constrain perception and thought. When these priors are relaxed, bottom-up sensory and emotional information flows more freely, allowing the system to revise deeply held beliefs and assumptions. This model provides a neuroscientific account of why psychedelic experiences can produce lasting changes in worldview, self-concept, and emotional patterns—and why the experiences are often described as "revealing" rather than "creating" new perspectives.
4. Psilocybin for depression — clinical evidence: Carhart-Harris led the first clinical trials of psilocybin for treatment-resistant depression at Imperial College, with striking results: patients who had not responded to conventional antidepressants showed rapid and sustained improvement after just one or two psilocybin sessions. Follow-up trials compared psilocybin to escitalopram (a standard SSRI) and found comparable efficacy with fewer side effects. These trials have been central to building the clinical evidence base for psilocybin therapy.
5. Connectedness as a mechanism of therapeutic change: Carhart-Harris has proposed that the therapeutic effects of psychedelics may be mediated by increased "connectedness"—both neurologically (greater connectivity between brain regions) and psychologically (greater feelings of connection to self, others, and the world). This framework links the neuroscience of psychedelics to broader themes in positive psychology, attachment theory, and contemplative practice.

Essential Writings

• "The Entropic Brain: A Theory of Conscious States Informed by Neuroimaging Research with Psychedelic Drugs" (Frontiers in Human Neuroscience, 2014): The paper that introduced the entropic brain hypothesis—one of the most cited and discussed theoretical papers in psychedelic science. Best use: the foundational theoretical text for understanding Carhart-Harris’s framework.
• "REBUS and the Anarchic Brain: Toward a Unified Model of the Brain Action of Psychedelics" (with Karl Friston, Pharmacological Reviews, 2019): The most comprehensive statement of the REBUS model, integrating free energy theory with psychedelic neuroscience. Best use: the essential paper for understanding the current leading theory of how psychedelics work in the brain.
• "Neural Correlates of the Psychedelic State as Determined by fMRI Studies with Psilocybin" (PNAS, 2012): The landmark imaging study showing DMN suppression under psilocybin. Best use: the original data behind the DMN-ego dissolution connection.
• "Trial of Psilocybin versus Escitalopram for Depression" (New England Journal of Medicine, 2021): The head-to-head comparison of psilocybin and a standard antidepressant. Best use: the most clinically significant trial for understanding psilocybin’s potential as a treatment for depression.

Image Attribution

Robin Carhart-Harris during meeting at the Centre for Psychedelic Research. Imperial Centre for Psychedelic Research, London. Photograph by Thomas Angus, Imperial College London, 23 July 2019, 18:01:53. Source: Sent by Thomas Angus, College Photographer and Image Manager, Imperial College London Images have been resized to 600pixels in accordance to Imperial College London Wikipedia image policy here: https://www.imperial.ac.uk/communications/photography/consent-and-permissions/