Recurrence Markers, Cognitive Burden and Neurobiological Homeostasis in Late-Life Depression

Inclusion Criteria: * Currently depressed participants (who will enter the treatment algorithm): 1) Age \> 60 years; 2) diagnosis of major depressive disorder, recurrent episode (DSM5); 3) severity: Montgomery Asberg Depression Rating Scale (MADRS) (67) ≥ 15; 4) cognition: Montreal Cognitive Assessment (MoCA) \>24 or Montreal Cognitive Assessment (MoCA) - BLIND ≥ 18; 5) fluent in English. * Remitted depressed participants (who will directly enter the longitudinal study): 1) Age \> 60 years; 2) diagnosis of major depressive disorder, recurrent, in partial or full remission (DSM5); 3) severity: MADRS \< 10; 4) cognition: MoCA \>24 or Montreal Cognitive Assessment (MoCA) - BLIND ≥ 18; 5) fluent in English. * Never- depressed elders: 1) Age \> 60 years; 2) severity: MADRS \< 8; 3) cognition: MoCA \>24 or MoCA - BLIND ≥ 18; 4) fluent in English. Exclusion Criteria: * Currently depressed participants (who will enter the treatment algorithm): 1) Other Axis I psychiatric disorders, except for simple phobia or anxiety disorders present during the depressive episode (e.g., generalized anxiety disorder (GAD) or panic disorder symptoms); 2) History of alcohol or drug dependence or abuse (other than nicotine) in the last year; 3) History of a developmental disorder or history of IQ \< 70; 4) Acute suicidality within 3 months of study entry; 5) Acute grief (\<1 month); 6) Current or past psychosis; 7) Primary neurological disorder, including dementia, clinical stroke, brain tumor, epile…