Age: 18 - 65
Healthy Volunteers: Not accepted
3.2 Inclusion Criteria
Depressed Participants:
1. Between the ages of 18 and 65 years old.
2. Capable of giving voluntary and informed consent.
3. Fluent in English.
4. Meet DSM-5 criteria for single or recurrent Major Depressive Disorder (current major depressive episode), confirmed via the Mini-International Neuropsychiatric Interview (MINI 6.086).
5. Moderate to severe depression severity, defined as a 17-item Hamilton Depression Rating Scale87 score ≥ 17.
6. Have had no initiation or dose change in any psychotropic medication in the four weeks prior to screening, as confirmed by the Antidepressant Treatment History Form (ATHF88).
7. If participating in psychotherapy, must have been in stable treatment for at least 3 months prior to entry into the study, with no anticipation of change in the frequency of therapeutic sessions, or the therapeutic focus over the duration of the study.
8. Can adhere to the study schedule.
9. Either a history of or no lifetime history of suicide attempt, confirmed via the Mini-International Neuropsychiatric Interview (MINI 6.086).
Nondepressed Participants:
1. Between the ages of 18 and 65 years old.
2. Capable of giving voluntary and informed consent.
3. Fluent in English.
4. No current or lifetime history of psychiatric diagnoses or suicidality, confirmed via the MINI 6.086.
5. Absent/non-clinical depression severity, defined as a 17-item Hamilton Depression Rating Scale87 < 8.
6. No history of antidepressant use, as measured by the ATHF88.
3.3 Exclusion Criteria
All Participants:
1. Are pregnant/lactating.
2. A MINI-confirmed diagnosis of major depressive disorder in people with bipolar disorder.
3. Other major medical comorbidities requiring immediate investigation or treatment, cardiac pacemaker, or implanted medication pump.
4. Lifetime history of psychosis, confirmed by the MINI 6.086, including schizophrenia, schizoaffective disorder, delusional disorder, or current psychotic symptoms.
5. Drug abuse or dependence within the last 6 months, excluding caffeine and nicotine.
6. Presence of contraindications for MRI, including metallic implants.
7. Have any significant neurological disorder or insult including, but not limited to: any condition likely to be associated with increased intracranial pressure, space occupying brain lesion, any history of seizure except those therapeutically induced by ECT, cerebral aneurysm, Parkinson's disease, Huntington's chorea, multiple sclerosis, dementia, significant head trauma with loss of consciousness for greater than or equal to 5 minutes.