Neurobiological Effects of Psilocybin in Treatment Resistant Bipolar Depression

This study is an open-label, single-arm, proof-of-concept study, wherein treatment resistant bipolar depression (TRBD) participants will receive one 25 mg dose of oral psilocybin accompanied by preparatory, monitoring, and integration psychotherapy sessions (psilocybin-assisted psychotherapy, or PAP). Using fMRI (functional magnetic resonance imaging), the findings of this study will provide data on the neurobiological mechanism of psilocybin in TRBD. The primary objective is to understand the dynamic role of amygdala activity by evaluating the neurobiological effects of a single psychedelic dose (25 mg) of oral psilocybin in individuals with a moderate to severe major depressive episode and a primary diagnosis of Bipolar II Disorder, with 2 or more failed treatment trials (i.e., treatment resistant bipolar depression \[TRBD\]). Neurobiological effects will be determined by evaluating the association between post-treatment right amygdala activity during the facial affect task (determined by fMRI one day after the psilocybin dose) and antidepressant effects (determined by changes in the Montgomery-Åsberg Depression Rating Scale \[MADRS\] scores over time, during the one-week period post-psilocybin dose). This is a single-arm, open-label clinical trial wherein all participants will receive the same study intervention. Hypothesis: Increased right amygdala activity on fMRI with emotional stimuli one day after psilocybin treatment will be associated with greater antidepressant effects in the one-week period post-treatment in individuals with TRBD.