Results on the spatial resolution of repetitive transcranial magnetic stimulation for cortical language mapping during object naming in healthy subjects

Background: The spatial resolution of repetitive navigated transcranial magnetic stimulation (rTMS) for language mapping is largely unknown. Thus, to determine a minimum spatial resolution of rTMS for language mapping, we evaluated the mapping sessions derived from 19 healthy volunteers for cortical hotspots of no-response errors. Then, the distances between hotspots (stimulation points with a high error rate) and adjacent mapping points (stimulation points with low error rates) were evaluated. Results: Mean distance values of 13.8 +/- 6.4 mm (from hotspots to ventral points, range 0.7-30.7 mm), 10.8 +/- 4.8 mm (from hotspots to dorsal points, range 2.0-26.5 mm), 16.6 +/- 4.8 mm (from hotspots to apical points, range 0.9-27.5 mm), and 13.8 +/- 4.3 mm (from hotspots to caudal points, range 2.0-24.2 mm) were measured. Conclusions: According to the results, the minimum spatial resolution of rTMS should principally allow for the identification of a particular gyrus, and according to the literature, it is in good accordance with the spatial resolution of direct cortical stimulation (DCS). Since measurement was performed between hotspots and adjacent mapping points and not on a finer-grained basis, we only refer to a minimum spatial resolution. Furthermore, refinement of our results within the scope of a prospective study combining rTMS and DCS for resolution measurement during language mapping should be the next step.