TMS-EEG Reliability: Bridging the Gap to Clinical Use

Concurrent transcranial magnetic stimulation (TMS) and electroencephalography (EEG), or TMS-EEG, holds the potential to broaden the clinical applications of TMS beyond its traditional role in evaluating the cortico-spinal tract and motor cortices. TMS-evoked potentials (TEPs) have emerged as valuable tools in clinical research, enabling the assessment of cortical excitability and effective connectivity between cortical regions in various psychiatric and neurological disorders and are increasingly recognized as a promising candidate biomarker for aiding in diagnosis and prognosis. Despite the well-established diagnostic utility of TMS, the clinical implementation of TMS-EEG has yet to meet the necessary standards. One critical aspect that often remains unaddressed is the reliability of TEP measurements. In this context, we outline the crucial reliability assessments required to determine the clinical applicability of TEPs. Firstly, we conduct a comprehensive review of the existing literature on reliability, encompassing both theoretical and statistical considerations. Subsequently, we present the current state of knowledge on TEP reliability. We emphasize the specific elements of reliability that must be incorporated to facilitate a unified, evidence-derived assessment of TMS-EEG as a clinical tool.