Full-Angle Rotating-Field TMS Stimulation and Initial Human Motor-Threshold Evaluation
DOI: Pending DOI
Synopsis
Rotating-field transcranial magnetic stimulation (rfTMS) was developed to reduce the strong dependence of conventional TMS on coil orientation by dynamically changing the direction of the induced field during a single stimulus. Our previously described implementation used two orthogonal stimulation channels with a controlled temporal phase offset to generate a rotating field spanning approximately 270°, thereby sampling multiple effective stimulation directions within one pulse and addressing orientation-specific constraints in cortical and experimental preparations. We have now developed an improved rfTMS approach that extends the rotating field trajectory to the full 360° plane. To assess the efficacy of this expanded angular coverage, we are now conducting an initial human pilot comparison between the established 270° rfTMS method and the new 360° implementation, using motor stimulation threshold as the primary readout of stimulation efficacy. Current results will be presented.
Background
Transcranial magnetic stimulation (TMS) excites neurons through current induced along axonal processes, making it inherently sensitive to the orientation of the induced electric field relative to axon geometry. We previously showed that rotating the induced field — generated by superposing two orthogonal, temporally phase-shifted coil pulses — relieves this orientation dependence and reliably excites systems that are difficult to stimulate with fixed-orientation coils, including 2D neuronal cultures and rat motor cortex (Rotem et al., PLOS ONE 2014). That implementation swept only 270° of a full rotation, leaving a residual directional asymmetry and excluding cortical regions where axons have no preferred orientation.
Methods
By adding precisely timed sequential excitation pulses, the resultant magnetic field vector is extended through the previously unsampled quadrant, producing full 360° planar field rotation. To evaluate physiological performance, we are conducting a within-subject pilot study in human motor cortex comparing the 270° and 360° rotating-field approaches. Motor stimulation threshold was selected as the primary physiological endpoint as it provides a quantitative measure of stimulation efficiency.
Results
Current results will be presented and discussed.
Discussion
Current results will be presented and discussed.
Disclosures
EM is an inventor of the original rfTMS.
All three authors are inventors of the extended rfTMS.
BrainsWay Ltd. is a licensee of the original rfTMS patent.
References
Rotem et al., PLOS ONE 2014 - https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0086794