Psilocybin links binocular rivalry switch rate to attention and subjective arousal levels in humans
This double-blind, placebo-controlled crossover study (n=10) investigated the effects of psilocybin (215 μg/kg) with and without the 5-HT2A antagonist ketanserin on binocular rivalry. It finds that psilocybin reduced the rate of perceptual switching, an effect that was not blocked by ketanserin despite the antagonist preventing other positive psychotic-like symptoms.
Authors
- Franz Vollenweider
Published
Abstract
Rationale
Binocular rivalry occurs when different images are simultaneously presented to each eye. During continual viewing of this stimulus, the observer will experience repeated switches between visual awareness of the two images. Previous studies have suggested that a slow rate of perceptual switching may be associated with clinical and drug-induced psychosis.
Objectives
The objective of the study was to explore the proposed relationship between binocular rivalry switch rate and subjective changes in psychological state associated with 5-HT2A receptor activation.Materials and methods: This study used psilocybin, the hallucinogen found naturally in Psilocybe mushrooms that had previously been found to induce psychosis-like symptoms via the 5-HT2A receptor. The effects of psilocybin (215 μg/kg) were considered alone and after pretreatment with the selective 5-HT2A antagonist ketanserin (50 mg) in ten healthy human subjects.
Results
Psilocybin significantly reduced the rate of binocular rivalry switching and increased the proportion of transitional/mixed percept experience. Pretreatment with ketanserin blocked the majority of psilocybin’s “positive” psychosis-like hallucinogenic symptoms. However, ketanserin had no influence on either the psilocybin-induced slowing of binocular rivalry or the drug’s “negative-type symptoms” associated with reduced arousal and vigilance.
Conclusions
Together, these findings link changes in binocular rivalry switching rate to subjective levels of arousal and attention. In addition, it suggests that psilocybin’s effect on binocular rivalry is unlikely to be mediated by the 5-HT2A receptor.
Research Summary of 'Psilocybin links binocular rivalry switch rate to attention and subjective arousal levels in humans'
Introduction
Binocular rivalry is a visual phenomenon in which two different images presented separately to each eye produce alternating conscious percepts: observers typically report seeing one image at a time, with intermittent mixed or transitional percepts. Earlier research has used rivalry to probe neural correlates of consciousness and perceptual grouping, and several studies have reported associations between rivalry switch rate and global changes in conscious state such as clinical psychosis, drug-induced altered states, and meditation. Standard mutual-inhibition models explain switching by local cortical interactions and neural fatigue, but they do not account well for links between switch rate and broader state variables such as arousal or attention. An alternative model posits that large fluctuations in brainstem nuclei (raphe, ventral tegmental area, locus coeruleus) and their neuromodulator release (serotonin, dopamine, noradrenaline) drive perceptual alternations. This study used the serotonergic hallucinogen psilocybin to test whether pharmacologically altering serotonin-mediated brain states changes binocular rivalry dynamics and whether those changes depend on 5-HT2A receptor activation. Carter and colleagues administered psilocybin (215 μg/kg) alone and after pretreatment with the selective 5-HT2A antagonist ketanserin (50 mg) in ten healthy volunteers, and compared these conditions with ketanserin alone and placebo. Binocular rivalry switching, the proportion of mixed percepts, and subjective measures of mood, arousal and altered states were measured at multiple time points to test whether psilocybin would slow switching and whether ketanserin would block that effect.
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Study Details
- Study Typeindividual
- Journal
- Compounds
- Topics
- Author
- APA Citation
Carter, O. L., Hasler, F., Pettigrew, J. D., Wallis, G. M., Liu, G. B., & Vollenweider, F. X. (2007). Psilocybin links binocular rivalry switch rate to attention and subjective arousal levels in humans. Psychopharmacology, 195(3), 415-424. https://doi.org/10.1007/s00213-007-0930-9
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