Which direction should I go? A quest for understanding the effect of TMS stimulus orientation on evoked responses

The orientation of the electric field (E-field) induced by transcranial magnetic stimulation (TMS) plays a significant role in determining the magnitude of motor evoked potentials (MEP) and TMS-evoked potentials (TEP). However, fundamental mechanisms explaining the interaction of the induced E-field and the underlying neuronal populations are still largely unknown. We recently entered a quest to understand and describe neurophysiological and physical factors affecting the effect of the E-field orientation on the MEP and TEP. We developed a dual-coil TMS transducer capable of fast and accurate electronic control of the induced E-field orientation. With this transducer, we could scan the effe…