Dissociable effects of psilocybin and escitalopram for depression on processing of musical surprises

Psilocybin therapy reduces anhedonia more than the SSRI escitalopram in major depressive disorder, yet escitalopram dampens emotional responses to musical surprises while psilocybin therapy preserves them. Escitalopram increases brain activity in memory and emotion regions during musical surprises, whereas psilocybin therapy decreases activity in the ventromedial prefrontal cortex and angular gyrus and increases sensory region activation. These contrasting neural and behavioral effects suggest fundamentally different treatment mechanisms: psilocybin may maintain subjective responses by reducing the salience of prediction errors or strengthening hedonic expectations, while escitalopram may weaken hedonic priors.

Study at a glance

Abstract

Abstract Psilocybin therapy (PT) is emerging as an effective intervention for Major Depressive Disorder (MDD), offering comparable efficacy to conventional treatments like selective serotonin reuptake inhibitors (SSRIs). Music, an emotionally evocative stimulus, provides a valuable tool to explore changes in hedonic and predictive processing mechanisms via expectancy violations, or ‘surprises’. This study sought to compare behavioural and functional magnetic resonance imaging (fMRI) responses to musical surprises in MDD patients treated with either PT or the SSRI, escitalopram. In this secondary analysis of a trial, 41 MDD patients (with usable fMRI data) were randomly assigned to either PT ( n = 22) or escitalopram ( n = 19) treatment groups. Participants listened to music during fMRI and tracked their emotional experience, both before and after a 6-week intervention. Surprise-related valence and arousal indices were calculated. Musical surprises were entered as regressors for whole-brain and region of interest fMRI analyses. PT caused a greater decrease in anhedonia scores compared with escitalopram. While escitalopram led to reductions in surprise-related affective responses, PT showed no significant change. Escitalopram was associated with increased activation in memory and emotional processing areas during musical surprises (versus control events) when compared with PT. Following PT, there was decreased activation in the ventromedial prefrontal cortex and angular gyrus, and greater activation in sensory regions. PT may allow for the subjective response to musical surprises to be maintained through a lasting reduction in the salience of prediction errors, or, alternatively, by increasing hedonic priors. Contrastingly, escitalopram may diminish hedonic priors, highlighting fundamental differences in treatment mechanisms.