REBUS Model (Relaxed Beliefs Under Psychedelics)
Developed by Robin Carhart-Harris, integrating predictive processing and Bayesian brain frameworks. · Carhart-Harris, R.L., & Friston, K.J. (2019). REBUS and the Anarchic Brain: Toward a Unified Model of the Brain Action of Psychedelics. (2019)
A neurocomputational model proposing that psychedelics reduce the precision of high-level priors (beliefs), allowing bottom-up sensory information to dominate and enabling a more unconstrained, flexible mode of cognition.
Core Concepts
The Problem
How do psychedelics produce such radical and varied changes in consciousness, from perceptual alterations to ego dissolution, in a mechanistically coherent way?
The Claim
Psychedelics act primarily by relaxing the influence of the brain's top-down predictions, particularly those encoded by the default mode and limbic networks, leading to a state where the brain is more open to new patterns and less constrained by prior knowledge.
Key Evidence
- •Functional MRI studies showing decreased connectivity and power in the default mode network under psilocybin and LSD.
- •MEG studies demonstrating increased signal diversity and entropy.
- •Correlations between DMN disintegration and ego-dissolution reports.
- •Consistency with predictive processing accounts of perception and belief.
Practical Implication
The model provides a framework for understanding therapeutic effects: by relaxing entrenched negative beliefs (maladaptive priors), psychedelics may allow for more adaptive re-weighting of experience, particularly in depression and addiction.
Nuance & Limits
REBUS emhasizes belief relaxation at multiple hierarchical levels, not just the DMN; and it does not claim that all effects are explained by this mechanism, as peripheral receptor actions also play a role.
Source Material
Citation Density
moderate
Gaps
- ⚠ Need for direct causal tests (e.g., perturbation studies) to show that belief relaxation is necessary for therapeutic effects.
- ⚠ How REBUS interacts with specific therapeutic modalities (e.g., cognitive behavioral therapy) post-session.
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