P299 Motor mapping with navigated transcranial magnetic stimulation: Does more stimuli increase the accuracy?

Abstract

Objectives Motor mapping with navigated transcranial magnetic stimulation (nTMS) is widespread technique that is used both in the preoperative planning and as a sign of neuroplasticity changes. But there is no generally accepted mapping protocol. The aim of our study was to estimate the relation between mapping parameters accuracy and the number of stimuli. Methods nTMS with flexor digitorum superficialis and extensor digitorum communis muscles cortical representation mapping was performed in 19 healthy volunteers, mean age 27. Total number of stimuli was not less than 200 in every session. We assessed the dependence of Center of Gravity (CoG) position, Area and Weighted Area on the number of stimuli by comparing the results while deleting randomly stimulation points except the Hot Spot. After determining of the number of analysing stimuli, the remaining ones were deleted randomly. First, we included in the analysis all stimulation points, then - only non-zero points. Results Standart deviations of the investigated parameters are different for different maps. For example, when 150 points were left, the mean value of Area’s SD was 27.77 mm2, and its dispersion was 13.46 mm2. The investigated relation when varying only non-zero points is close to linear, while it’s nonlinear with all points. Thus, precise mapping of the area’s borders seems to be more important than stimulation in its center. At least 80 border’s stimuli should be applied for correct estimation. Conclusions Evaluation of the accuracy of map’s integrated parameters is crucial for the control of studies based on these parameters. The proposed estimation methods and their use on real data allows to identify qualitative and quantitative patterns of accuracy and to optimize the mapping protocol.