Translated from our German original by AI. The German text was researched, written, and edited by the Psychedelia Foundation team and remains the authoritative version.
The search for a reliable biological marker of psychedelic states of consciousness could be more complicated than assumed so far. A new review questions the widespread assumption that increased brain entropy (the entropic brain hypothesis) can already count as a robust biomarker of the effects of serotonergic psychedelics.
The Entropic Brain Hypothesis has been one of the most influential models in psychedelic research for years. It assumes that substances such as LSD and psilocybin increase the diversity and unpredictability of neural activity patterns, measurable as increased entropy in the brain. Numerous neuroimaging studies have described such changes, which is why brain entropy has become established in parts of the field as a promising candidate for an objective marker of the psychedelic state.
The authors of the newly published review warn, however, against an overly simplified interpretation. There are still indications that entropy measurements can provide valuable information about altered states of consciousness, they write. The evidence available so far is not sufficient, though, to regard brain entropy as a reliable or specific biomarker of the psychedelic state.
In their analysis, the researchers identify four central challenges. First, changes in brain entropy can be observed not only under psychedelics but also outside such states. Second, existing entropy models do too little justice to the fact that consciousness is not a one-dimensional phenomenon but comprises several dimensions of subjective experience. Third, there are various entropy metrics that capture different aspects of neural dynamics and do not always deliver consistent results. Fourth, the direct link between elevated entropy values in the brain and a consciousness experienced subjectively as “richer” or “expanded” has so far only been empirically supported to a limited degree.
Despite this criticism, the researchers do not discard the concept. Instead they argue for more precise methodological approaches, standardized measurement procedures, and a closer link between neurobiological data and systematically collected subjective reports of experience.
