Abstract
While serotonin reuptake inhibitors are sometimes used in clinical practice to treat acute bipolar depression, the neurophysiological substrates underlying their efficacy are little studied. In the context of a larger clinical efficacy trial, the present study explored neural mechanisms associated with citalopram versus placebo treatment for bipolar depression. FDG-PET imaging examined whole-brain metabolic changes before and after treatment. Clinical efficacy was similar for citalopram versus placebo. Neuroimaging results demonstrated greater glucose metabolism in the left orbitofrontal cortex (OFC) before treatment (combined citalopram and placebo subjects) relative to after treatment, but did not correlate with clinical recovery. Glucose metabolism in the left OFC was also a predictor of depression severity when baseline scans were regressed with baseline MADRS scores. Despite of our small sample size and possibly underpowered whole-brain analysis approach, these preliminary results suggest the OFC, a key region involved in reward circuity, may be a neural substrate for depressive symptom improvement in bipolar depression, regardless of whether due to active treatment or placebo.