The entropic brain hypothesis was set out in 2014 by Robin Carhart-Harris and colleagues. Based on psilocybin imaging data, it argues that the psychedelic state shows elevated entropy, a measure of disorder or unpredictability, in aspects of brain activity, and that normal waking consciousness sits just below a “critical” point between order and disorder (Carhart-Harris et al., 2014).
In 2019 the idea was folded into REBUS, “relaxed beliefs under psychedelics”, which proposes that psychedelics loosen the weight the brain gives to its high-level assumptions so that bottom-up information flows more freely (Carhart-Harris and Friston, 2019). Both are presented as models to be tested.
The tests are mixed. A 2026 study of psilocybin fMRI data found that 8 of 14 published entropy measures showed no consistent effect and that the measures correlated poorly with each other (McCulloch et al., 2026). A 2026 pooled DMT EEG analysis found brain rhythms moved away from criticality toward the more ordered side, against the hypothesis’s prediction (Irrmischer et al., 2026). The framework is influential but unproven.
Sources
- Carhart-Harris et al., 2014, Frontiers in Human Neuroscience: The entropic brain
- Carhart-Harris and Friston, 2019, Pharmacological Reviews: REBUS
- McCulloch et al., 2026, Nature Communications: entropy measures
- Irrmischer et al., 2026, Journal of Neuroscience: DMT and criticality
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