gms | German Medical Science

Objective: The examination of neuropsychological cortical function by transcranial magnetic stimulation (TMS) was used as a non-invasive technique in healthy subjects before. Especially for face recognition, categorization, calculation, and line bisection, bihemispheric parietal localization was shown. Yet, this study was designed to investigate the precision and applicability of navigated repetitive TMS (rTMS) for mapping of these four neuropsychological cortical functions in order to establish this technique for preoperative mapping in brain tumor patients.

Method: 20 healthy, purely right-handed subjects (11 female, 9 male) underwent rTMS language mapping using 5Hz/10impulses (0 ms delay). Both hemispheres were investigated in a randomized way with two weeks delay between mappings of each hemisphere. 52 previously determined cortical spots of the whole hemisphere were stimulated on both sides. In every mapping the subjects were instructed to perform the four different tasks (face recognition, categorization, calculation, line bisection) while rTMS pulses were applied. The rTMS induced errors were categorized into 6 to 13 different error types, depending on the task, respectively. Error rates (subjects with induced errors per number of stimulated subjects) were calculated for each task and stimulation point.

Results: The highest error rates (for all errors without hesitation) in face recognition were observed in the left frontal lobe (triangular inferior frontal gyrus (trIFG): left 40%, right 35%). In the categorization task the highest error rates were located mostly in the right parietal lobe (middle post-central gyrus (mPoG): 20%, angular gyrus (AnG): 20%) and the left frontal lobe (posterior middle frontal gyrus (pMFG): 20%). The calculation task showed its highest error rate in left hemisphere frontal lobe (middle middle frontal gyrus (mMFG): 30%, parietal lobe (AnG: 30%), and right hemisphere frontal lobe (middle pre-central gyrus (mPrG): 30%). The line bisection task showed the highest error rates bilateral in every lobe with 10% error rates, (conspicuous accumulated in the right AnG: 10%, right dorsal lateral occipital gyrus (dLOG): 10%, and right ventral lateral occipital gyrus (vLOG): 10%).

Conclusions: rTMS seems feasible to locate distinctive neuropsychological functions. Clinical usefulness for preoperative mapping in brain tumor patients has to be evaluated as the upcoming step.