Inclusion Criteria

• Ages aged 50-85 
• Diagnosis of unipolar major depressive disorder without psychotic features, determined by the SCID
• Montgomery-Åsberg Depression Rating Scale (MADRS) score ≥ 20
• Mini Mental Status Exam (MMSE) ≤ 1 SD below the mean score for patient's age and education
• Off antidepressants or on a stable dose of an antidepressant for 8 weeks and do not intend to change the dose in the next 10 weeks
• Capacity to provide written consent for research assessment and treatment

Exclusion Criteria

• Intent or plan to attempt suicide in the near future
• History or presence of psychiatric diagnoses other than major depressive disorder without psychotic features, generalized anxiety disorder, or specific phobia
• Use of psychotropic drugs or cholinesterase inhibitors other than use of ≤ 0.5 mg of lorazepam daily up to seven times per week
• Neurological disorders (dementias, history of stroke, multiple sclerosis, Parkinson's disease, epilepsy, etc.); cardiac, renal, or respiratory failure; severe chronic obstructive pulmonary disease; metastatic cancer; or debilitated states or less common medical illnesses that may either influence brain systems of interest or ability to participate in the study. Dr. Alexopoulos or another research psychiatrist will review any medical illnesses that does not appear in the list above and determine whether it interferes with the study of positive valence system functions in depression.
• Contraindications to MRI scanning including cardiac pacemaker, heart valve replacement, vascular stent, insulin pump, cochlear implant, any other metallic biomedical implant contraindicating to MRI, and claustrophobia