TMS motor evoked potential input-output curves predict the neuroplasticity effects of continuous theta burst stimulation

Abstract

Objective: Continuous theta burst stimulation (cTBS), a form of repetitive transcranial magnetic stimulation (rTMS) known for its inhibitory effects, shows variable responses between individuals, potentially due to differences in neuroplasticity. This study explores whether motor evoked potential (MEP) input–output (IO) parameters measured prior to neuromodulation can predict responses to cTBS. Methods: IO curves were sampled from healthy adults by recording MEPs over a range of single-pulse TMS intensities to obtain parameters including MEPmax and S50 (midpoint intensity). Subjects later received cTBS (80% AMT, low intensity) over the same location of motor cortex, and their MEPs before and after stimulation were compared. Results: Both MEPmax and S50 predicted responses, significantly correlating (p < 0.05, R2 > 0.25) with individuals’ MEP changes from 10 to 30 min after cTBS. We also validated an easily implementable biomarker not requiring time-consuming sampling of full IO curve: MEP130RMT (median of 10 MEPs at 130 % RMT), which strongly predicted cTBS response (p < 0.005, R2 > 0.3). Head-to-head comparison against a genetic biomarker of rTMS responses (BDNF polymorphism) showed that IO based predictors had superior performance in explaining response variability. Conclusion: IO curves derived prior to neuromodulation quickly, reliably predict cTBS-induced changes in cortical excitability. Significance: This work provides an accessible strategy for stratifying responders in diagnostic and therapeutic applications of rTMS; potentially boosting response rates to brain stimulation.