P221 Psilocybin Accelerates EEG Microstate Transitions and Elevates Approximate Entropy
Filip Novický1*, Adeel Razi2,3,4, Fleur Zeldenrust1
1Donders Institute for Brain, Cognition and Behaviour, Radboud University, Heyendaalseweg 135, Nijmegen, 6525 AJ, Netherlands 2Turner Institute for Brain and Mental Health, Monash University, Clayton, 3168, Victoria, Australia 3Wellcome Centre for Human Neuroimaging, University College London, London, WC1N 3AR, UK 4CIFAR Azrieli Global Scholars Program, CIFAR, Toronto, Canada
*Email: filip.novicky@donders.ru.nl Introduction
While psilocybin’s therapeutic potential is well-documented, its effects on brain function remain incompletely understood. The relaxed beliefs under psychedelics (REBUS) theory proposes that psychedelics weaken the brain's rigid thought patterns by reducing the influence of existing mental frameworks and hence increasing neural entropy [1]. This study investigated how psilocybin affects the brain’s spatiotemporal dynamics at the millisecond scale using EEG. In addition, this study examined whether its effects are modulated by mindfulness training and different cognitive states.
Methods We analyzed EEG data from 63 participants (33 with mindfulness training, 30 without) during four conditions: video watching, resting state, meditation, and music listening, both before and after the consumption of psilocybin (19mg). Using EEG microstate analysis, we examined the temporal characteristics of four canonical brain states [2]. We complemented this with approximate entropy analysis to quantify signal complexity [3]. Statistical comparisons were performed across conditions, groups, and drug states with FDR correction.
Results Psilocybin significantly altered brain dynamics during the eyes-closed conditions, increasing microstates’ occurrences rates while decreasing their duration. Mindfulness training showed no significant effect on these changes. Approximate entropy analysis revealed increased signal complexity, particularly during the eyes-closed states. While brain activity patterns primarily differed between eyes-open and eyes-closed states, psilocybin notably diminished the typical neural activity differences between passive rest and attentional states (meditation and music).
Discussion Our findings support the REBUS theory’s prediction of an increased entropy of the neuronal activity under psychedelics, particularly during the eyes-closed states. The combination of increased microstate transition rates and elevated signal complexity suggests psilocybin creates a more dynamic and less constrained brain state, in agreement with previous studies [4]. Thus, the results of this study suggests that psychedelics can temporarily alter the brain’s typical processing patterns.
Acknowledgements This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No. 953327. This work benefited from the guidance of Adeel Razi's lab regarding the PsiConnect dataset. References 1. https://doi.org/10.1124/pr.118.017160 2.https://doi.org/10.1016/j.neuroimage.2017.11.062 3.https://doi.org/10.1073/pnas.88.6.2297 4. https://doi.org/10.1038/srep46421
