Measurement and Modeling of the Effects of Transcranial Magnetic Stimulation on the Brain

Transcranial magnetic stimulation (TMS) is a method of noninvasively modulating the excitability of the brain. TMS relies on the principle of electromagnetic induction in producing an electric field that stimulates neurons. Measuring the effect of TMS in real time and being able to determine its spatiotemporal resolution increase its potential in both research and clinical applications. In this article, the authors model the electric fields of three TMS coils: quadruple butterfly coil (QBC), triple halo coil (THC), and the magventure B65 coils, by performing computational finite-element (FE) analysis using the Sim4life software. To evaluate the accuracy of the electromagnetic models, we devised a novel experimental protocol that compares the maximum field intensity stimulated using modeling with the induced voltage experimentally measured within a phantom brain in response to TMS.