Temporal interference for dual site transcranial magnetic stimulation

Abstract

Dual-site Transcranial Magnetic Stimulation (ds-TMS) is a TMS protocol that involves stimulating two areas of the brain in close succession. This method is useful for studying the connections between two physical parts of the brain. TMS coils are generally designed for use on a single target area in the brain. When ds-TMS targets are in close proximity to one another, using traditional coils in a limited space increases the possibility of errors associated with positioning, resulting in inconsistent pulse strength and trajectory. We developed a single TMS coil that uses temporal interference (TI) to stimulate multiple targets within close proximity without compromising the ideal positioning of either location. TI TMS operates based on the frequency difference of two magnetic fields delivered simultaneously. The frequency difference between the two fields results in an envelope which can be steered to target a different location without moving the coil. We designed a TI-TMS coil and show that the peak induced electric field can be steered 4 cm in either direction (8 cm range) from the center point of the coil while delivering a peak field of 120 V/m, which is above the minimum 100 V/m needed to activate neurons. An experimental model was built using the same dimensions as the simulation model and validated that the physical model is able to steer the magnetic pulse using TI.