Title & Introduction
- Paper Title: Psilocybin Alters Visual-Contextual Computations
- Published In: bioRxiv (Preprint)
- Publish Date: February 8, 2025
- Authors: Marco Aqil, Gilles de Hollander, Nina Vreugdenhil, Tomas Knapen, Serge O. Dumoulin
- Objective: To investigate the effects of psilocybin on visual contextual perception and brain responses using psychophysics, ultra-high field fMRI, and computational modeling.
- Importance: Understanding how psilocybin alters contextual computations in the brain may provide insights into its broader cognitive and perceptual effects, including potential therapeutic applications.
Summary & Takeaways
Key Takeaway: Psilocybin significantly alters visual contextual processing, increasing susceptibility to the Ebbinghaus illusion and reducing surround suppression in early visual cortex, indicating fundamental changes in perceptual organization.
Practical Application: These findings suggest that psilocybin may alter brain computations in a way that enhances sensitivity to context, which could have implications for both therapeutic interventions and understanding the neural mechanisms underlying altered states of consciousness.
Key Background Information
- Context: Psychedelics like psilocybin are known to alter perception, but the computational mechanisms behind these changes remain unclear. Vision provides a measurable framework for studying these effects.
- Hypothesis: Psilocybin alters visual-contextual computations by modulating neural responses in the visual cortex, particularly through mechanisms such as surround suppression.
Methodology
- Study Design: Randomized, double-blind, placebo-controlled, crossover design.
- Participants: 18 healthy adults (data from 12 included in final analysis).
- Intervention/Exposure: Participants received placebo, 5mg, or 10mg psilocybin in separate sessions.
- Controls: Placebo condition served as the control.
- Duration: Sessions spaced at least two weeks apart, with behavioral and neuroimaging assessments conducted in each session.
Key Findings
Primary Outcomes:
- Psilocybin increased susceptibility to the Ebbinghaus illusion by 39% (5mg) and 59% (10mg) compared to placebo.
- Visual perception of size in the illusion was altered in a dose-dependent manner, with psilocybin increasing contextual modulation.
- Psilocybin reduced surround suppression in early visual cortex (V1-V3), as measured by ultra-high-field fMRI.
Secondary Outcomes:
- Computational modeling indicated that psilocybin’s effects were best explained by a reduction in a specific neural activation parameter linked to contextual processing.
- Changes in visual-contextual computations correlated with participants’ subjective visual experiences under psilocybin.
- Results were consistent across multiple analytical approaches, ruling out confounding effects of noise or hemodynamic changes.
Interpretation & Implications
- Conclusion: Psilocybin fundamentally alters visual contextual computations, reducing suppression mechanisms that normally regulate perception.
- Implications: The findings suggest that altered contextual processing may be a core mechanism underlying psychedelic effects, with potential relevance for understanding altered states of consciousness and clinical applications in disorders involving perceptual rigidity.
- Limitations: Small sample size, use of only moderate doses (5mg and 10mg), and focus on visual perception limit generalizability to other cognitive domains.
Researchers & Publication
- Researchers: Marco Aqil, Gilles de Hollander, Nina Vreugdenhil, Tomas Knapen, Serge O. Dumoulin
- Publication Name: bioRxiv (Preprint)
- Study URL: Link to preprint
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