Introduction

The 40 Hz ASSRs is a key measure of the brain's rhythmic entrainment to auditory stimuli, with disruptions linked to schizophrenia. While glutamatergic models have shown similar disturbances, the role of serotonergic 5-HT2A receptors remains unclear. This study examines the impact of psilocybin, a serotoninergic psychedelic inducing psychosis-like cognitive effects, on the 40 Hz ASSR in healthy volunteers.

Goal

Focusing on the nexus between serotonin receptor modulation and neural mechanisms governing auditory responses, our work contributes to understanding the complex interplay in cognitive disruptions observed in psychosis and psychedelic experience. We expected to observe decreased phase-locking and amplitude of 40 Hz ASSR.

Methods and Analysis

Twenty healthy volunteers (10M/10F) were given psilocybin orally in ratio 0.26mg/kg. Design of the study is crossover, double blind and placebo controlled. Auditory steady-state responses were recorded using 256 channel EEG four times – before ingestion and in the peak of intoxication.

Main Findings

To assess the effect of psilocybin on auditory steady-state responses three indexes were used: evoked amplitude, event-related spectral perturbation and index of phase coherence between epochs (phase locking index). 175 channels with focus on fronto-central electrodes were used for analysis. The results show that psilocybin reduced the phase synchronization and amplitude of 40 Hz auditory steady-state response compared with placebo in the peak of intoxication. 

Conclusion

Study showed that psilocybin lowered the synchronization level and the amplitude of 40 Hz auditory steady-state responses. The result yields further support for the role of gamma oscillations in cognitive processing and its disturbance.