🫠 Psychonaut POV

[5-min read] Q&A with Robin Carhart-Harris, Researcher & Professor

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Robin Carhart-Harris is widely recognized as one of the leading psychedelic scientists and thinkers in the world. And even he has changed his mind about—and with—these substances.

We asked Robin how he fell into psychedelic research, what his most popular psychedelic theories tell us about the human mind, and what unanswered questions he’d like to investigate next.

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Robin Carhart-Harris Psychonaut POV
What initially drew you to studying psychedelics?

In my early 20s, while studying for my master's at Brunel University in West London, I became deeply fascinated by the field of psychoanalysis. I admired it for its guts, for its bravery. It takes courage to look deeply into one’s soul, explore one’s hidden thoughts, and try to uncover the truth. We can critique psychoanalysis all we want, but there’s a beautiful honesty about it that has always resonated with me.

During that period, though, I began questioning whether psychoanalysis was the best tool to understand the unconscious mind. It’s such a slippery and abstract thing, but I had a feeling the unconscious was real. Maybe there were better methods to get a hold of it. In a seminar, I raised the question of whether drugs could serve as a more direct route to the unconscious. This inquiry led me to discover the work of Stanislav Grof on the human unconscious and the role of psychedelics. That discovery profoundly influenced my career direction and sparked what I might call a lifelong passion.

Now, looking back over the past 20 years, it's clear that this moment was a turning point for me. Ever since, I’ve been exploring the depths of the human mind.

Since you began your psychedelic research career, is there anything significant that you've changed your mind about?

Initially, I was quite skeptical of psychedelic therapy. My personal experiences with psychedelics weren't entirely positive, and the prevailing cultural and scientific attitudes two decades ago were largely dismissive, if not outright negative, towards these substances. My interest was purely academic. At that time, I saw psychedelics as tools for consciousness research, not as medicines.

However, my perspective began to shift once I was involved in brain imaging research with psychedelics. Seeing the changes in brain function, particularly reductions in blood flow to areas typically overactive in depression, prompted me to reconsider their therapeutic value. We already knew that other depression treatments—from psychotherapy to SSRIs to deep-brain stimulation—similarly reduced activity in these regions. This evidence, alongside participants' subjective reports of feeling lighter and unburdened after sessions, suggested psychedelics had real therapeutic potential.

Over time, my stance evolved from skepticism to cautious optimism, as a result of direct observation and scientific inquiry. The publication of pivotal studies in the early 2000s from the likes of Roland Griffiths and Charlie Grob further solidified my belief in the potential of psychedelics for mental health treatment. By the turn of the 2010s, having witnessed the profound effects of psilocybin therapy firsthand, I became a proponent.

Today, my conviction is rooted in rigorous research and patient outcomes. But of course, I can admit it’s a little silly to have dismissed the longstanding traditional use of psilocybin mushrooms in visionary healing practices. In the West, we were late to jump on that. In fact, we used psychedelics as models of psychosis.

Can you explain your “overlearning hypothesis”? What does it say about the root cause of psychiatric conditions, and what are the implications for psychedelic therapy?

Yes, it’s the idea that much of psychopathology may stem from problematic learning and repetition. For instance, addiction involves a form of overlearning where individuals become attached to objects of relief. Depression is characterized by repetitive, exhaustive thoughts, while anxiety involves a feedback loop of increasing worry. This repetitive nature is also evident in conditions like OCD with its intrusive thoughts, which spill into compulsive behaviors.

The idea of canalization, introduced to me by Karl Friston, provided a framework for understanding these phenomena. Canalization refers to the development of deeply ingrained paths in our mental and behavioral responses, much like water carving deeper channels in a landscape. This concept suggests that our responses can become overly rigid and resistant to change.

Psychedelic therapy is especially interesting to me because it can disrupt these entrenched patterns. My work explores how these substances might offer a means to reset or loosen these deeply carved mental channels. I believe psychedelics can help us understand and potentially reverse some of the problematic learning underlying many mental health issues.

Setting psychedelics aside for a moment, the overlearning hypothesis also offers us a more empathetic perspective on why certain maladaptive behaviors or thought patterns develop in the first place. When we recognize these symptoms for what they are—defense mechanisms against underlying negative emotions or experiences—it challenges the conventional, biological-centric view of mental illness. It should also steer therapists and providers toward a compassionate approach that acknowledges individuals' experiences and the functional role their symptoms may serve.

Another of your major contributions to psychedelic theory is the REBUS model. Can you elaborate on this concept and any insights it might offer into the nature of consciousness?

The REBUS model, which stands for Relaxed Beliefs Under Psychedelics, is informed by the Bayesian brain hypothesis and hierarchical predictive processing, primarily influenced by Karl Friston's work. This model suggests that the brain operates through internal predictive models or assumptions, which significantly shape our perception of the world. These assumptions are mostly implicit, and we're often unaware of their influence on our sensory experience. Psychedelics, according to this model, modulate the precision weighting of these assumptions, essentially altering how strongly they influence us.

You can think of precision weighting as the confidence level in our assumptions. Under psychedelics, there's an increase in variance, meaning our assumptions become less rigid and our minds more open to alternative interpretations of sensory input. The data points scatter away from a tight correlation line, so to speak. This entropic effect under psychedelics seems to lead to a more fluid and less constrained consciousness.

In terms of consciousness, the REBUS model offers insights and raises interesting questions about how the mind and brain interact. It aligns with the idea that consciousness emerges from internal assumptions and their interplay with sensory input. Psychedelics disrupt this interaction, loosening the grip of entrenched patterns of thought and behavior. As we already discussed, these especially fluid mental states may be what underlie psychedelics' therapeutic benefits in psychiatry and beyond.

If you could empirically answer any question about psychedelics that has remained a mystery so far, what would it be?

I do wonder, could psychedelics be useful in the treatment of disorders of consciousness? The underlying hypothesis hinges on the entropic brain principle. If psychedelics increase the entropy—or the variance and complexity—of brain activity, then perhaps they could enhance the richness of conscious experience in conditions where brain activity is significantly diminished, such as in comas and vegetative states.

However, the use of psychedelics in this context raises some serious ethical and practical questions. The primary goal for many families and caregivers, of course, is the full recovery of their loved ones. Psychedelics might give the patient an enrichment of phenomenal consciousness, but it may not necessarily bring back their cognitive functions or self-awareness. We simply don’t know, and that’s one of the reasons these situations are so sensitive.

Despite these challenges, the interest in researching psychedelics for disorders of consciousness is growing. These conditions are currently beyond the reach of conventional medicine, and there’s a chance psychedelics could break through. We assume patients want to come back as who they were beforehand, and certainly families want their loved one back. To me, it’s a very interesting philosophical and scientific question whether that’s possible.

Want more from Robin?

Dig into his papers, past interviews, and harm reduction resources on the Carhart-Harris Lab website.

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DISCLAIMER: This newsletter is for educational and informational purposes only and is not intended as a substitute for professional medical advice. The use, possession, and distribution of psychedelic drugs are illegal in most countries and may result in criminal prosecution.

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