Biomarkers of Depression and Treatment Response

This study uses brain imaging and biological tests to understand why some people with major depression respond to treatment and others don't. Participants will receive non-invasive brain stimulation therapy and have brain scans taken before and after treatment to identify markers of response. **You may be eligible if...** - You are 18–70 years old - You have been diagnosed with major depressive disorder (MDD) and are currently in a depressive episode without psychotic features - Your depression is moderate-to-severe (MADRS score above 19) - You have tried 1–4 antidepressant medications in this episode without full relief - You are willing to undergo non-invasive brain stimulation and attend visits for about 8 weeks - You can read and speak English **You may NOT be eligible if...** - You have a current psychotic disorder (e.g., schizophrenia) - You have a neurological condition such as epilepsy, dementia, or a history of significant head trauma - You have a metal implant in or near your head (e.g., pacemaker, aneurysm clips) - You have a primary diagnosis of generalized anxiety disorder during this episode - You have had a seizure - You have a current substance use disorder (within the past 6 months) Talk to your doctor to see if this trial is right for you.