TMS motor mapping: method overview, research and clinical application

Cortical representations of muscles can be probed non‑invasively using transcranial magnetic stimulation (TMS) motor mapping. TMS mapping can be applied both in research and clinical settings to assess motor cortex reorganization under the influence of various factors, to clarify pathophysiological mechanisms of motor system damage in various diseases, and to develop novel biomarkers of this damage. The article discusses the main methodological aspects of TMS motor mapping: choosing stimulation intensity and interstimulus interval, using of grid, neuronavigation and robotic systems, determining of a target muscle, etc. Special attention is paid to the cortical motor representation parameters such as the “hot spot” and center of gravity localization, area, etc. and their reproducibility under various mapping protocols. A review of publications on the use of TMS motor mapping application in brain tumors, stroke and amyotrophic lateral sclerosis is presented. The most significant practical impact of TMS motor mapping of the cortex is seen in brain tumors when used for presurgical localization of eloquent motor areas, as it is associated with the improvement of functional outcomes and progression‑free survival.