Reduced brain responsiveness to emotional stimuli with escitalopram but not psilocybin therapy for depression

Psilocybin therapy is an emerging intervention for depression that may be at least as effective as standard first-line treatments i.e., Selective Serotonin Reuptake Inhibitors (SSRIs). Here we assess neural responses to emotional faces (fear, happy, and neutral) using Blood Oxygen-Level Dependent (BOLD) functional Magnetic Resonance Imaging (fMRI) in two groups with major depressive disorder: 1) a ‘psilocybin group’ that received two dosing sessions with 25mg plus six weeks of daily placebo, and 2) an ‘escitalopram group’ that received six weeks of the SSRI escitalopram, plus two dosing sessions with an inactive/placebo dose of 1mg psilocybin. Both groups had an equal amount of psychological support throughout. An emotional face fMRI paradigm was completed at baseline (pre-treatment) and at the six-week post-treatment primary endpoint (three weeks following psilocybin dosing sessions). An analysis examining the interaction between patient group (psilocybin vs. escitalopram) and time-point (pre-vs. post-treatment) showed a robust effect in a distributed network of cortical brain regions. Follow-up analyses showed that post-treatment BOLD responses to emotional faces of all types were significantly reduced in the escitalopram group, with no change, or even a slight increase, in the psilocybin group. Specific analyses of the amygdala showed a reduction of response to fear faces in the escitalopram group, but no effects for the psilocybin group. Despite large improvements in depressive symptoms in the psilocybin group, psilocybin-therapy had only a minor effect on brain responsiveness to emotional stimuli. We suggest that reduced emotional responsiveness may be a biomarker of SSRIs’ antidepressant action that is not shared by psilocybin-therapy.