LSD-induced increases in social adaptation to opinions similar to one's own are associated with stimulation of serotonin receptors

Introduction

Adapting one's attitudes and behaviours to group norms is central to social interaction, yet the neuropharmacology underpinning social influence processing in humans is poorly understood. Previous neuroimaging work has implicated frontal regions and reward circuitry, including the medial prefrontal cortex (mPFC) and ventral striatum, in responses to mismatches between personal and group opinions. While dopamine and oxytocin have been linked to aspects of social adaptation, the role of the serotonin (5-HT) system—particularly the 5-HT2A receptor—remains unclear. Classic psychedelic lysergic acid diethylamide (LSD) acts at multiple serotonin and dopamine receptor subtypes and is known to alter social cognition and brain connectivity, offering a pharmacological tool to probe 5-HT2A contributions to social influence. Duerler and colleagues set out to test whether LSD modulates behavioural adaptation to group opinion and the neural processes that support it, and whether any LSD effects depend on 5-HT2A receptor stimulation. They used a double-blind, randomised, placebo-controlled, within-subject crossover design to compare placebo, LSD (100 µg), and ketanserin (40 mg, a selective 5-HT2A antagonist) pre-treatment followed by LSD. The main behavioural metric was the Weight of Advice (WOA) score, which quantifies change toward a presented group norm; functional MRI (fMRI) was used to identify brain regions whose activity during social feedback and decision-making was altered by LSD and by ketanserin pre-treatment.