Inclusion Criteria 

• At least 60 years old 
• Major depressive disorder without psychotic features 
• Not on antidepressants or on a stable does for the past 12 weeks 
• Montgomery-Asberg Depression Rating Scale score ≥ 20 
• Mini-Mental State Examination score ≥ 24 
• Off antidepressants or on a stable dose for 12 weeks without intent to change dose 
• Capacity to consent 

Exclusion Criteria 

• Intent or plan to attempt suicide 
• Current psychiatric diagnosis other than Major Depressive Disorder, Persistent Depressive Disorder, Generalized Anxiety Disorder, or specific phobia
• History of past psychiatric diagnoses other than MDD, PDD, or anxiety disorders (separation, specific phobia, social phobia, panic, agoraphobia, GAD) 
• Use of psychotropic drugs or cholinesterase inhibitors (other than a stable dose of an antidepressant or benzodiazepines ≤ 0.5mg, ≤ 5x/week) 
• Serious medical conditions such as neurological disorders, severe COPD, metastatic cancer, cardiac/renal/respiratory failure, other condition that influences neural systems