A new protocol for multiple muscle mapping using nTMS

Abstract

AbstractBackgroundSingle-pulse transcranial magnetic stimulation is a safe and non-invasive tool for investigating cortical representation of muscles in the primary motor cortex. While non-navigated TMS has been successfully applied to simultaneously induce motor-evoked potentials (MEPs) in multiple muscles, a more rigorous assessment of the corresponding cortical representation can greatly benefit from navigated transcranial magnetic stimulation (nTMS).ObjectiveWe designed a protocol to map the entire precentral gyrus using neural navigation while recording responses of eight muscles simultaneously. Here, we evaluated the feasibility, validity, and reliability of this protocol.MethodTwenty participants underwent conventional (i.e., muscle-based, grid-constrained) and gyrus-based nTMS mapping. For both protocols, we investigated three different stimulation intensities during two consecutive sessions.ResultsThe gyrus-based nTMS mapping was received well by all participants and was less time consuming than the grid-constrained standard. On average, MEP amplitudes, latencies, and centre-of-gravity and size of the active areas largely agreed across protocols supporting validity. Intraclass coefficients between sessions unscored the reliability of our protocol.ConclusionWe designed an nTMS protocol for the simultaneous mapping multiple muscles on the cortex. The protocol takes only about ten minutes per participant when including as many as eight muscles. Our assessments revealed that the cortical representation of multiple muscles can be determined with high validity and reliability.