Intracranial Recording During TMS: A Practical Guide

Transcranial magnetic stimulation (TMS) has emerged as a powerful clinical tool for treating neuropsychiatric conditions, yet our understanding of how TMS modulates neural circuits in the human brain remains limited. While decades of research have established the therapeutic efficacy of TMS, fundamental questions persist about the spatial and temporal dynamics of TMS effects, including which brain regions are activated and modulated, how long neural changes persist, and the mechanisms underlying the antidepressant effect. Combining transcranial magnetic stimulation and intracranial electroencephalography (TMS-iEEG) can fill this gap by providing important insights into how the human brain responds to non-invasive stimulation. TMS-iEEG enables investigation of both local cortical responses and network-level propagation with millisecond temporal resolution and precise spatial localization. This chapter provides an overview for conducting TMS-iEEG experiments. We first detail phantom validation procedures for evaluating potential heating, electrode displacement, and induced currents. We then outline safety monitoring protocols for human participants, including continuous electrophysiological monitoring for epileptiform activity. Finally, we outline procedures to perform TMS-iEEG experiments – from equipment setup through data collection and analysis. When properly implemented, TMS-iEEG can reveal both immediate local effects and network-level responses to TMS that are not accessible through conventional recording approaches, providing critical insights into the mechanisms of brain stimulation.