Optimization of the navigated TMS mapping algorithm for accurate detection of plasticity and abnormalities in cortical muscle representations

Abstract

Navigated TMS mapping of cortical muscle representations allows noninvasive assessment of the 11 state of a healthy or diseased motor system and monitoring its change with time. These applications are 12 hampered by the heterogeneity of existing mapping algorithms and the lack of detailed information about their 13 accuracy. We aimed to find an optimal motor evoked potential (MEP) sampling scheme in the grid-based 14 mapping algorithm in terms of the accuracy of muscle representation parameters. The APB muscles of eight 15 healthy subjects were mapped three times on consecutive days using a seven-by-seven grid with ten stimuli 16 per cell. The effect of the MEP variability on the parameter accuracy was assessed using bootstrapping. The 17 accuracy of representation parameters increased with the number of stimuli without saturation up to at least 18 ten stimuli per cell. The detailed sampling showed that the between-session representation area changes in the 19 absence of interventions were significantly larger than the within-session fluctuations and thus could not be 20 explained solely by the trial-to-trial variability of MEPs. The results demonstrate that the number of stimuli 21 has no universally optimal value and must be chosen by balancing the accuracy requirements with the mapping 22 time constraints in a given problem. 23