The relation between naturalistic use of psychedelics and perception of emotional stimuli: An event-related potential study comparing non-users and experienced users of classic psychedelics

Introduction

Psychedelics such as psilocybin, LSD, mescaline and DMT produce robust alterations of perception and consciousness, and a growing body of laboratory and clinical research has examined their acute neurophysiological and subjective effects. Earlier experimental studies report that psychedelics can acutely alter behavioural and neural responses to emotional stimuli: for example, reduced recognition of sad and fearful faces, lowered amplitude of face-selective ERP components (N170) to negative faces, reduced P300 responses to negatively valenced words, and decreased amygdala reactivity and connectivity when processing negative emotional cues. Some longitudinal and cross-sectional work further suggests longer-lasting increases in positive affect and decreases in negative affect after psychedelic sessions, but these findings derive mostly from controlled clinical or laboratory settings and self-report measures that are vulnerable to bias. Orłowski and colleagues set out to test whether similar alterations in emotional reactivity are associated with naturalistic use of classic psychedelics (i.e. use outside supervised clinical or lab contexts). The present pre-registered cross-sectional EEG study compared experienced naturalistic psychedelic users (≥15 lifetime experiences) with non-users while participants performed a gender discrimination task on faces showing neutral, angry, fearful or happy expressions. The main hypotheses concerned two pre-registered ERP indices of emotional processing (N170 and P300): users were expected to show attenuated N170 and P300 amplitudes to negative expressions (fear, anger) relative to non-users. Exploratory analyses targeted earlier attention/perception-related components (N200 and P200) to provide a fuller picture of processing from early perceptual stages to later cognitive evaluation.