Major Depressive Disorder (MDD) is common in Veterans and is the leading cause of disability worldwide. Unfortunately, many Veterans with MDD do not respond to conventional pharmacological interventions. TMS offers a noninvasive, nonpharmacological treatment option that is effective for treatment- resistant MDD. This therapeutic approach uses repetitive pulsed magnetic fields to induce depolarization in brain regions that, in turn, modulate neural networks and alter pathological patterns of brain activity seen in depression. TMS lacks the systematic side effects associated with pharmacological treatments for MDD and is generally well-tolerated and safe. Furthermore, there is emerging literature supporting the use of TMS for a wide range of neuropsychiatric disorders for which pharmacotherapy offers limited efficacy. Despite this therapeutic promise, TMS remains an underutilized psychiatric treatment. Challenges limiting more widespread adoption of TMS include the time commitment for patients and clinicians and variable responses to treatment. Understanding this variability in treatment response would help optimize the delivery of TMS to Veterans, increase the percentage of successful treatments, and provide a starting point for integrating measurement-based care approaches with TMS protocols. This CDA2 proposes an approach to understand this variability in TMS treatment response and optimize TMS treatments in Veterans inexpensively. This project will utilize clinical data from several hundred Veterans who have received and will receive TMS for the treatment of depression as part of the nationwide “VA TMS Pilot Program”. This multisite VA effort was designed to both deliver clinical TMS to Veterans with MDD and provide a mechanism for VA scientists to investigate TMS outcomes and predictors of treatment response. A key feature of this program is the implementation of a standardized REDCap database that is used to collect data from clinical questionnaires as part of the VHA Measurement-Based Care initiative. These instruments measure various aspects of psychiatric symptomology. Over 1000 Veterans have begun TMS through this program. This project will use this clinical longitudinal data to replicate and expand a nonlinear modeling approach of the TMS treatment response that we have developed using clinical data from our lab (n=97) as well as published group-level data from multiple large clinical trials of TMS. This nonlinear modeling approach uses an exponential decay function to quantify the magnitude, speed, and outcome of TMS treatment response that utilizes all of the time points of symptom ratings before, during, and after TMS treatment. This provides a comprehensive estimate of the total TMS treatment course as well as an approach to predict treatment response. This CDA2 will replicate and expand this work using the largest dataset of TMS response in Veterans to date and will potentially yield precision psychiatry tools that would be widel...