Current medical therapies for depression take weeks to achieve full efficacy, and are ineffective in many patients or cause intolerable side effects, emphasizing the need for a deeper understanding of depression and its treatment. Identifying early brain biomarkers of treatments responses seems necessary to improve antidepressant treatment outcome. In this study we aim to detect early brain responses to a fast acting antidepressant-like treatment administered intravenously during a Real-Time Neurofeedback functional magnetic resonance imaging (MRI) Task to predict antidepressant treatment outcome in depression. At completion of the neuroimaging task, participants will enter a placebo-controlled clinical trial with a selective serotonin reuptake inhibitor (SSRI).