The Entropic Brain: Dr. Robin Carhart-Harris’s Theory of Consciousness

What the Entropic Brain Hypothesis Says

Why does five minutes on 5-MeO-DMT feel less like watching a movie and more like being unmade? One of the most cited answers in psychedelic science comes from Dr. Robin Carhart-Harris, who introduced the entropic brain hypothesis in 2014 with Dr. David Nutt at Imperial College London. The idea borrows a concept from thermodynamics: entropy, the measure of disorder within a system. Carhart-Harris proposed that the richness of a conscious state can be indexed by the entropy of spontaneous brain activity — too little, and consciousness narrows into rigid, repetitive patterns, as seen in depression or addiction; too much, and the sense of a coherent self can dissolve altogether, which is where classic psychedelics and 5-MeO-DMT in particular come in.

Under normal waking consciousness, the brain runs on a set of well-worn predictive pathways. Sensory information flows up from the senses while expectations flow down from higher-order brain regions, a process rooted in what’s known as the Bayesian brain model. Layer 5 pyramidal neurons, dense with serotonin 5-HT2A receptors, sit at the center of this balancing act. Psychedelics bind directly to these receptors, and in doing so, push the brain away from its habitual grooves.

Entropy, the Default Mode Network, and the 5-MeO-DMT Parallel

Using fMRI and MEG, Carhart-Harris’s team found that psilocybin reduced activity and connectivity in the Default Mode Network (DMN) — the network most associated with self-referential thought, memory, and rumination. Its key hub, the posterior cingulate cortex, quiets down considerably. Since DMN hyperactivity is linked to depression and rigid self-narratives, this induced disorder appears to loosen the grip of overly rehearsed thought patterns, giving the mind room to reorganize.

5-MeO-DMT research shows a related but distinct signature: EEG studies report a global reduction in alpha power alongside decreases in posterior beta waves, consistent with the disruption of top-down models like self-perception. Where psilocybin unfolds gradually over hours, 5-MeO-DMT compresses a similar entropic spike into fifteen to twenty minutes, which may explain why the experience is often described less in visual terms and more as a total, if brief, dissolution of the subject-object divide — what Carhart-Harris and Karl Friston later formalized as the REBUS model, or “relaxed beliefs under psychedelics.”

Final Thoughts

Carhart-Harris’s framework doesn’t claim to resolve what consciousness ultimately is, but it does give researchers a measurable proxy — entropy — for something that was previously only described in first-person terms. It also reframes the psychedelic state itself: not as noise, but as a temporary widening of the brain’s repertoire, with real implications for how rigid patterns of thought might be interrupted therapeutically. Debate continues over how far the analogy between thermodynamic entropy and subjective experience can be pushed. If you’re curious about this territory, approach it thoughtfully, and speak with a qualified professional before taking any exploratory steps.