Study of Brain Response to Emotional Pictures Using a Magnetic Resonance Imaging (fMRI) While on Escitalopram

Inclusion Criteria: * Ages 18-50 years and able to give voluntary informed consent. * Satisfy criteria for Major Depressive Disorder (MDD) and current depressed episode using the Mini International Neuropsychiatric Interview (M.I.N.I.). * 17-item Hamilton Depression Rating Scale (HDRS) score \> 18. * Satisfy criteria to undergo an MRI scan based on MRI screening questionnaire. * Able to be managed as outpatients for initial assessment and during treatment as ascertained by the following - * Symptoms not worsening by more than 10 points on the HDRS during the course of the study. * No danger to self or others. Exclusion Criteria: * Meeting DSM-IV criteria for schizophrenia, schizophreniform disorder, schizoaffective disorder, bipolar disorder, atypical psychosis, mental retardation, or organic mental (including organic mood) disorder. * On monoamine oxidase inhibitors in the past 2 weeks. * History of narrow angle glaucoma. * Lack of response of the current episode of depression to two or more adequate courses of antidepressant therapy at a clinically appropriate dose for a minimum of 4 weeks or, in the judgment of the investigator, the patient meets criteria for treatment-resistant depression. * Use of neuroleptic in the past 2 weeks. * Use of antidepressants in the past 2 weeks. If on fluoxetine in the past, then should not have been on this medication for 4 weeks. * Use of mood stabilizers in the past 2 weeks. * Use of benzodiazepines in the past 2 weeks. * Acutely suicidal or homicidal or requiring inpatient treatment. * Meeting DSM-IV criteria for other substance dependence within the past year, except caffeine or nicotine. The criteria will be evaluated by interview and urinary toxicology screening initially and on test days. * Use of alcohol in the past 1 week. * No serious medical or neurological illness as assessed by physical examination and laboratory examination including CBC and blood chemistry. * Current pregnancy or breast-feeding. * Metallic implants. * Previously known positive HIV blood test as reported by the subject.