Accelerated Intermittent Theta Burst in Treatment-Naive Adolescents

Inclusion Criteria: 1. Male or Female, between the ages of 13 and 20 at the time of screening. 2. Able to read, understand, and provide written, dated assent and/or consent prior to screening. Proficiency in English sufficient to complete questionnaires and follow instructions during aiTBS interventions. Stated willingness to comply with all study procedures, including availability for the duration of the study, and to communicate with study personnel about adverse events and other clinically important information. 3. Diagnosed with Major Depressive Disorder (MDD) with a current Major Depressive Episode (MDE), according to the criteria defined in the Diagnosis and Statistical Manual of Mental Disorders, Fifth Edition, Text Revision (DSM-5). 4. No prior major depressive episodes (MDEs) as determined by MINI-KID 5. CDRS-R score of ≥40 at screening (Visit 1). 6. Treatment-naive as determined by the ATHF (no adequate antidepressant trials prior to screening defined as fewer than 12 weeks of antidepressant medication in the past 2 years and fewer than 10 psychotherapy sessions for depression in the past year; willingness to taper medications and stop psychotherapy if recently started and within the window defined above.) 7. TMS naive. 8. Access to ongoing psychiatric care before and after completion of the study. 9. In good general health, as evidenced by medical history. 10. Agreement to adhere to Lifestyle Considerations throughout study duration. Exclusion Criteria: 1. Pregnancy 2. High-risk for suicide or active suicidal ideation as determined by clinical interview 3. The presence or diagnosis of prominent anxiety disorder, or dysthymia (\>4 on SAPAS; \>16 on GAD-7) 4. Current severe insomnia (must sleep a minimum of 5 hours each night before stimulation) 5. Current mania or psychosis 6. Bipolar Affective Disorder and/or primary psychotic disorders. 7. Autism Spectrum disorder or Intellectual Disability 8. A diagnosis of obsessive-compulsive disorder (OCD) 9. Current moderate or severe substance use disorder or demonstrating signs of acute substance withdrawal. 10. Urine screening test positive for illicit substances. 11. Any history of ECT (greater than 8 sessions) without meeting responder criteria 12. Recent (during the current depressive episode) or concurrent use of a rapid acting antidepressant agent (i.e., ketamine or a course of ECT). 13. History of significant neurologic disease, including dementia, Parkinson's or Huntington's disease, brain tumor, unexpected seizure/epilepsy disorder, subdural hematoma, multiple sclerosis, or history of significant head trauma. 14. Untreated or insufficiently treated endocrine disorder. 15. Contraindications to receiving rTMS (e.g., metal in head, history of seizure, known brain lesion) 16. Contraindications to MRI (ferromagnetic metal in their body). 17. Any current or past history of any physical condition which in the investigator's opinion might put the subject at risk or interfere with study results interpretation. 18. Depth-adjusted aiTBS treatment dose \> 65% maximum stimulator output (MSO) 19. Treatment with another investigational drug or other intervention within the study period. 20. Any other condition deemed by the PI to interfere with the study or increase risk to the participant.