The study focuses on understanding how Behavioral Activation (BA) therapy affects the brain of depressed teenagers using a special type of scan called fMRI (functional magnetic resonance imaging). This scan helps see which parts of the brain are active during different tasks. The study aims to find out if BA therapy changes brain activity related to avoiding activities because of low motivation or fear. Healthy teens will also participate for comparison.

The study will include adolescents aged 15-17. There will be 136 participants, including 96 with depression and 40 healthy ones. During the study, teenagers will have several fMRI scans to see changes in brain activity and behavior.

• Participants will have several fMRI scans over time.
• Only adolescents aged 15-17 with specific health criteria can join.
• Participants can't take certain medications before and during the study.

Depressed teens must have technology like a smartphone or computer to complete some parts of the study. Teens with certain health issues, like severe mental disorders or a history of substance abuse, cannot join. It's a chance to help scientists understand how therapy might help improve depression in teens.