Inclusion Criteria:  Good general health DSM-5 diagnosis of major depressive disorder (MDD)  Exclusion Criteria:  General Exclusion Criteria:  Pregnancy  Medical Conditions:  Moderate to severe traumatic brain injury (>30 min. loss of consciousness or >24 hours posttraumatic amnesia) or other neurocognitive disorder with evidence of neurological deficits. Presence of co-morbid medical conditions not limited to but including cardiovascular (e.g., history of acute coronary event, stroke) and neurological diseases (e.g., Parkinson's disease), as well as pain disorders. Presence of an uncontrolled medical condition that is deemed by the investigators to interfere with the proposed study procedures, or to put the study participant at undue risk.  Psychiatric Disorders:  Current severe suicidal ideation or attempt within the past 12 months. Psychosis Bipolar disorder Substance abuse or dependence within the previous 6 months  Contraindications for MRI:  Bodily implants of unsafe paramagnetic materials such as pace-makers and aneurysm clips. Claustrophobia that is severe enough to preclude MRI scanning.  Medications:  Evidence of recreational drug use from a urine test.