The Entropic Brain: A Theory of Conscious States Informed by Neuroimaging Research with Psychedelic Drugs

The Default Mode Network Is Not a Brain Region but a Neuroimaging Portrait of the Ego

Robin Carhart-Harris’s 2014 paper, “The Entropic Brain,” accomplishes something rare in neuroscience: it offers a theoretical framework capacious enough to hold both empirical data and the phenomenological traditions it implicitly invokes. The central proposition is deceptively simple. Normal waking consciousness, governed by the default mode network (DMN), operates in a state of relatively low entropy — high predictability, tight integration, constrained repertoire of neural states. Psychedelic compounds, by agonizing 5-HT2A serotonin receptors, dramatically increase cortical entropy, desynchronize the DMN, and push the brain into a state of richer, less predictable activity. What makes this more than pharmacology is the interpretive frame Carhart-Harris builds around it. The DMN, he argues, functions as the neural substrate of the narrative self — the autobiographical “I” that maintains temporal continuity, self-referential rumination, and the boundary between self and world. Greg Mahr, writing from within Jungian scholarship, captures the implication directly: “We can think of the DMN metaphorically as a neurophysiological correlate of the ego.” DMN suppression under psilocybin thus becomes, in depth-psychological terms, ego dissolution — not as metaphor but as measurable neural event. The entropic brain hypothesis gives imaging-grounded specificity to what Jung called abaissement du niveau mental, the depotentiation of conscious personality that opens access to collective unconscious material. Jung recognized that fever, fasting, religious fervor, and (reluctantly) psychedelic drugs could induce this state. Carhart-Harris shows what it looks like on an fMRI scan.

Entropy Is Not Chaos but the Psyche’s Native Multiplicity Reasserting Itself

The deepest contribution of the entropic brain model is its revaluation of disorder. In standard psychiatric nosology, increased neural entropy reads as pathology — the loosening of associative structure seen in early psychosis, the fragmentation of identity in dissociative states. Carhart-Harris does not deny these parallels; he maps psychedelic states and psychotic onset onto the same high-entropy end of his spectrum. But he insists on a critical distinction: the psychedelic state is transient and occurs within a container of set and setting, whereas psychosis is entropy without return. This distinction carries enormous weight for depth psychology. James Hillman’s entire project in The Dream and the Underworld rests on the claim that the dayworld ego’s grip on phenomena must be loosened — that “pathologizing” is the soul’s native movement toward depth, not a failure to be corrected. Hillman’s critique of ego psychology’s drive to normalize finds unexpected empirical support in Carhart-Harris’s data: the most therapeutically efficacious psychedelic sessions correlate with the most profound ego dissolution, the greatest subjective entropy. The rigid, low-entropy brain is not the healthy brain; it is the depressed brain, the addicted brain, the brain caught in what Mahr identifies as the “negative, judgmental ruminations” of hyperactive DMN function. Hillman wrote that “the pervading, though masked, depression in our civilization is partly a response of the soul to its lost underworld.” Carhart-Harris’s neuroimaging data put a startling empirical edge on that claim: depression correlates with increased DMN connectivity, with the ego’s stranglehold on neural real estate tightening rather than relaxing.

The Reducing Valve Returns — Now with Neuroimaging Evidence

Carhart-Harris explicitly invokes Aldous Huxley’s “reducing valve” theory of consciousness, itself drawn from Henri Bergson. The brain, on this account, does not generate consciousness so much as constrain it — filtering the overwhelming totality of potential experience into the narrow stream useful for biological survival. Joseph Campbell, discussing Stanislav Grof’s LSD research, quoted Huxley at length on this point: “The function of the brain and nervous system is to protect us from being overwhelmed and confused by this mass of largely useless and irrelevant knowledge.” Carhart-Harris transforms this philosophical speculation into a testable neuroscientific hypothesis. Under psilocybin, the reducing valve opens. The brain’s entropic state increases, cross-modal communication expands (visual cortex talking to emotional processing centers, for instance), and the subject experiences what the paper frames as a broadened state space — more possible configurations of consciousness available per unit time. The therapeutic implications are immediate: treatment-resistant depression, addiction, end-of-life anxiety all involve pathological narrowing of the state space, a collapse of possibility into repetitive, self-referential loops. The psychedelic intervention does not add new content; it removes the filter that prevents existing neural capacities from communicating. This is not a metaphor borrowed from mysticism. It is a prediction derived from information theory and confirmed by blood-oxygen-level-dependent imaging. Yet it converges with astonishing precision on what Richard Tarnas described as the depth-psychological project of “moving beyond the narrow concerns and limitations of its illusory separateness, and opening awareness to the larger realities and claims of the collective psyche.”

Why This Paper Remains Essential to Any Serious Encounter with Depth Psychology and Neuroscience

Jung’s wariness about psychedelics — expressed in his letters to Victor White and A. M. Hubbard — rested on legitimate concerns about premature exposure to collective unconscious material and the ego’s inability to integrate what it encounters. Carhart-Harris does not dismiss these concerns; his model implicitly validates them by showing that the therapeutic benefit of high-entropy states depends entirely on the capacity for re-integration — the return to a reorganized, slightly less rigid low-entropy state afterward. The entropic brain is not a celebration of dissolution for its own sake. It is a formal account of why controlled, temporary dissolution — what Mahr calls the psychedelic experience conducted with “careful protocols, with extensive pre- and post-trip psychotherapy” — produces lasting psychological reorganization. For anyone navigating between the phenomenological richness of depth psychology and the empirical demands of contemporary neuroscience, this paper is the single most important theoretical bridge. It does not reduce Jung to neuroscience or inflate neuroscience into mysticism. It demonstrates that the psyche’s movement between constraint and release, ego and Self, surface and depth, has a measurable thermodynamic signature — and that healing lives in the oscillation, not at either pole.