The investigators will be comparing brain (neural) activation of depressed adolescent patients before, during and after a course of Behavioral Activation (BA) therapy using functional magnetic resonance imaging (fMRI). In particular, the project seeks to determine whether BA targets different neural mechanisms for behavioral avoidance associated with low motivation as compared to threat avoidance. A group of healthy controls will also be scanned as a comparator group for behavioral and imaging measures.

The primary aim of this study is to investigate the behavioral and neurobiological factors predicting response to Behavior Activation (BA), a psychosocial treatment for Major Depressive Disorder (MDD), in adolescents.

The recruitment age pool will be adolescents ages 15-17. The investigators plan to recruit 40 healthy controls and 96 treatment-seeking adolescents for an overall sample of ~136 participants, Individuals who reach the age of majority (18) during the study will be re-consented as adults and allowed to continue participating in the study.

A healthy control group will be included to assess stability in behavioral and neuroimaging measures over the course of participation in the study.

The fMRI scan schedule will include three task-based sessions (baseline, after session 7, and after endpoint) and two (sessions 3 & 9). "behavioral-scheduling-in-the-scanner" sessions Primary results will focus on symptom change within patients and their association to measures of low motivation and threat avoidance.

Inclusion Criteria:

• Male and female adolescents ages 15-17;
• current MDD diagnosis as determined by K-SADS-PL,
• CDRS-R raw score > 45 (T-score > 65) at baseline;
• estimated full scale IQ > 80 as determined by the WASI-II;
• able to receive outpatient care;
• willing to not partake in other psychosocial treatments;
• not taking psychotropic medications in the two weeks (four weeks for fluoxetine) prior to consent, with the exception of psychostimulant medication prescribed for the treatment of ADHD.
• Additionally, depressed patients must have access to required technology (e.g. smart phone, tablet, or desktop computer) to complete the EMA portion of the study.
• Healthy controls cannot not meet criteria for MDD and their CDRS-R raw score must be below 28; T-score < 52).

Exclusion Criteria:

• Current or past diagnosis of bipolar, schizophrenia, schizophreniform, schizoaffective disorders, or psychosis NOS;
• current diagnosis of developmental disorder, severe conduct disorder, life-threatening anorexia, OCD, or autism-spectrum disorders;
• taking psychotropic medications prior to entry;
• estimated IQ < 80; alcohol/drug dependence or abuse within the last 3 months;
• potential/confirmed neurological disorder or epilepsy;
• claustrophobia;
• presence of a medical condition that precludes fMRI;
• endorsement of imminent and serious suicidality;
• medical conditions that take precedence over the presence of MDD;
• pregnancy;
• substance use (excluding nicotine) within two weeks of the fMRI scan;
• left-handedness;
• nicotine use within 3 hours of the fMRI scan;
• history of traumatic brain injury or of being unconscious for more than 30 minutes;
• a stimulant regime for ADHD which has changed within 30 days of the fMRI scan.
• Non-compliance (i.e. <70% completion) or inability (i.e. lack of smartphone device) to complete the 3 assessment periods of EMA.

De-identified data (including access and additional documents) will be shared through the NIMH NDA and in accordance with NIMH NDA data-sharing policy.

As soon as possible after data collection.

In accordance with NIMH NDA data-sharing policy.