Processing of self-related thoughts in experienced users of classic psychedelics : a source localisation EEG study

Background: Psychedelics have gained increasing interest in scientific research due to their ability to induce profound alterations in perception, emotional processing and self-consciousness. However, the research regarding the functioning of individuals who use psychedelics in naturalistic contexts remains limited.bAims: Here we aim to explore psychological and neurophysiological differences between naturalistic psychedelics users and non-users in terms of processing of self-related thoughts.bMethods: We use behavioural testing combined with electroencephalography (EEG) with source localisation. To mitigate potential confounding effects of personality traits and personal history which makes one willing to take psychedelics, we compared users to individuals who did not take psychedelics, but are intending to do so in the future. To ensure robustness of our results, we included two datasets collected at two different laboratories.bResults: The results from Dataset I (N = 70) suggest that during self-related thoughts psychedelics users exhibit weaker increases in alpha and beta power in comparison to non-users, primarily in brain regions linked to processing of self-related information and memory (such as posterior cingulate cortex). However, analysis of Dataset II (N = 38) did not replicate the between-group effects, possibly due to the smaller sample size and spatial resolution limitations.bConclusions: While non-replicability restricts interpretation of our findings, our research expands the ongoing discussion on strength and duration of the psychedelic effects, specifically in brain circuits associated with self-related processing, and its relationship to well-being. Our results fit into growing scepticism about the specificity of the role of default-mode network hubs in changes associated with psychedelics experience.