Inclusion Criteria:  Age 18-60 Physically healthy Willing and able to provide informed consent  5. Diagnosis of MDD or No history of mental illness  Exclusion Criteria:  Pregnancy or lactation (women of reproductive potential must have a negative urine pregnancy screen) Post-partum state (being within 2 months of delivery or miscarriage) Homicide risk as determined by clinical interview A lifetime history of psychotic disorder Any history of dissociation or dissociative disorder Bipolar disorder Pervasive developmental disorder Cognitive disorder Cluster A personality disorder Borderline personality disorder Anorexia nervosa Alcohol or drug dependence (except nicotine and caffeine) within the last month or the use of any hallucinogen (except cannabis), including phencyclidine in the last month (NOTE that a positive UDS is not exclusionary except for hallucinogens, methamphetamine, or cocaine. People presenting intoxicated with alcohol may be included when a Breathalyzer test (Alco-Sensor IV) is negative as long as there is no history of recent dependence. Recent myocardial infarction Unstable angina Active neoplasm in the past 6 months Immunosuppressive or corticosteroid therapy within the last month, with the following exceptions: any inhaled, intranasal, topical or vaginal corticosteroids are allowed. Chemotherapy Head injury with loss of consciousness in the past 6 months