Accelerated Theta Burst in Treatment-Resistant Depression: A Dose Finding and Biomarker Study

Inclusion Criteria: * Male or female, 18 to 75 years of age. * Able to provide informed consent. * Diagnosed with Major Depressive Disorder (MDD) or bipolar affective disorder 2 and currently experiencing a Major Depressive Episode (MDE). * prior exposure to rTMS * Participants must qualify as "moderate or severe treatment refractory" using the Maudsley staging method. * Participants may continue antidepressant regimen, but must be stable for 6 weeks prior to enrollment in the study. They must maintain that same antidepressant regimen throughout the study duration. * Participants are required to have a stable psychiatrist for the duration of study enrollment. Exclusion Criteria: * History of MI, CABG, CHF, or other cardiac history * Any neurological conditions * History of epilepsy * OCD * Independent sleep disorder * Autism Spectrum Disorder