REBUS and the Anarchic Brain: Toward a Unified Model of the Brain Action of Psychedelics

Summary & key facts

This paper proposes a clear model for how classic psychedelics change the brain and experience. The authors call the model REBUS, short for relaxed beliefs under psychedelics, and the idea is that psychedelics make the brain's spontaneous activity more variable. That variability loosens the brain's high-level expectations or beliefs, so lower-level signals from emotions and memory can get through more easily. The model helps explain many features of the psychedelic experience and suggests why, with the right care and setting, psychedelics such as psilocybin might help people revise deeply stuck beliefs that underlie some mental health problems.

Key facts:

• The authors built a single model called REBUS that merges two earlier ideas: one about how the whole brain predicts the world and another about how psychedelics increase brain signal variability.
• REBUS says psychedelics reduce the brain's confidence in its high-level expectations or beliefs, which the paper explains as making those beliefs more open to new information.
• This change happens because psychedelics increase the entropy of spontaneous brain activity, meaning the brain's activity becomes more variable and less tightly controlled.
• The paper suggests that opening up high-level beliefs lets bottom-up signals from emotion and memory have more influence, which can permit revision of entrenched, problematic beliefs.
• The authors say this process could help explain many features of psychedelic experiences and why, when combined with careful therapeutic support, psychedelics might produce lasting psychological change.
• The paper notes that psilocybin therapy is moving through mid-stage clinical trials and that some people expect regulated access to psilocybin within about ten years, but it presents REBUS as a theoretical model that needs ongoing testing.

Abstract

This paper formulates the action of psychedelics by integrating the free-energy principle and entropic brain hypothesis. We call this formulation relaxed beliefs under psychedelics (REBUS) and the anarchic brain, founded on the principle that—via their entropic effect on spontaneous cortical activity—psychedelics work to relax the precision of high-level priors or beliefs, thereby liberating bottom-up information flow, particularly via intrinsic sources such as the limbic system. We assemble evidence for this model and show how it can explain a broad range of phenomena associated with the psychedelic experience. With regard to their potential therapeutic use, we propose that psychedelics work to relax the precision weighting of pathologically overweighted priors underpinning various expressions of mental illness. We propose that this process entails an increased sensitization of high-level priors to bottom-up signaling (stemming from intrinsic sources), and that this heightened sensitivity enables the potential revision and deweighting of overweighted priors. We end by discussing further implications of the model, such as that psychedelics can bring about the revision of other heavily weighted high-level priors, not directly related to mental health, such as those underlying partisan and/or overly-confident political, religious, and/or philosophical perspectives. Significance Statement Psychedelics are capturing interest, with efforts underway to bring psilocybin therapy to marketing authorisation and legal access within a decade, spearheaded by the findings of a series of phase 2 trials. In this climate, a compelling unified model of how psychedelics alter brain function to alter consciousness would have appeal. Towards this end, we have sought to integrate a leading model of global brain function, hierarchical predictive coding, with an often-cited model of the acute action of psychedelics, the entropic brain hypothesis. The resulting synthesis states that psychedelics work to relax high-level priors, sensitising them to liberated bottom-up information flow, which, with the right intention, care provision and context, can help guide and cultivate the revision of entrenched pathological priors.

Topics

Biochemical Analysis and Sensing Techniques Neurotransmitter Receptor Influence on Behavior Psychedelics and Drug Studies

Categories

Clinical Psychology Psychology Social Sciences

Tags

Action (physics) Artificial intelligence Bayesian probability Cognitive psychology Computer science Consciousness Epistemology Hallucinogen Neuroscience Philosophy Physics Prior probability Psilocybin Psychiatry Psychology Quantum mechanics

Substances

Psilocybin

Conditions & symptoms

Depression PTSD Sadness or low mood