Novel TMS-derived metrics enable machine learning classification of major depressive disorder

No validated biomarker currently exists for early detection or personalized treatment of major depressive disorder (MDD). Transcranial magnetic stimulation (TMS) is widely used in clinical and research settings and holds promise for biomarker discovery. We assessed two novel TMS-derived cortical excitability metrics, $\delta$ and $\varrho$ , for distinguishing individuals with MDD from healthy controls. Motor-evoked potentials (MEPs) were recorded from the left abductor pollicis brevis during TMS of the right primary motor cortex in twenty-six unmedicated MDD patients and seventeen never-depressed controls. $\delta$ and $\varrho$ were computed from peak-to-peak MEP amplitudes. A Gradient Boosting classifier predicted diagnostic status using raw MEPs, $\delta$ and $\varrho$ , or their combination. While MEPs alone were non-predictive, $\delta$ and $\varrho$ significantly improved accuracy. Combining MEPs with $\delta$ and $\varrho$ yielded 83.3% accuracy and 82.3% balanced accuracy. These results suggest $\delta$ and $\varrho$ effectively capture neurophysiological alterations in MDD and support their potential as candidate biomarkers for MDD.