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

Introduction

Classic psychedelics (for example LSD, psilocybin, mescaline, DMT) produce acute alterations in perception, emotion and self-consciousness that have prompted renewed scientific interest. Prior controlled clinical and healthy-participant studies link supervised psychedelic use with sustained improvements in well-being and reductions in symptoms such as depression and anxiety. Alterations in the processing of self-related information, and reductions in maladaptive self-focused thinking such as rumination, have been proposed as one potential mechanism for these therapeutic effects. However, much of the evidence comes from laboratory-based or questionnaire studies; comparatively little work has examined behavioural and physiological correlates of self-related processing in naturalistic, experienced psychedelic users outside clinical trials. Ruban and colleagues set out to fill this gap by comparing experienced, naturalistic users of classic psychedelics with matched non-users on behavioural and electrophysiological responses during an experimental induction of self-related thoughts. The investigators focused on cortical oscillatory activity in alpha (7–12 Hz) and beta (14–30 Hz) bands within source-localised regions, reasoning that prior work has implicated these bands and the default mode network (DMN) in self-related processing and in acute psychedelic effects. They preregistered confirmatory hypotheses that users would show lower rumination and greater reflection on questionnaire measures, that SRT (self-related thoughts) induction would increase alpha and beta power in DMN regions, and that these increases would be smaller in users than non-users; exploratory analyses probed effects outside the predefined regions and controlled for potential confounders such as meditation and cannabis use.