gms | German Medical Science

Objective: Over the past years navigated transcranial magnetic stimulation (rTMS) had become increasingly important for the preoperative examination and mapping of eloquent brain areas. Among other things it was demonstrated that the detection of neuropsychological function, like calculation or face recognition, seems feasible with rTMS. Since the avoidance of postoperative impairment are of broad interest in neurosurgery and neuroscience this study now aims on the investigation of the cortical mapping of categorization function via rTMS.

Methods: 20 volunteers (11 female, 9 male) purely right-handed and without any medical deficiency underwent rTMS mapping for cortical categorization function using 5 Hz/10 pulses. 52 cortical spots spread over the whole hemispheres were stimulated. Both hemispheres were examined randomly with 2 weeks delay between both mappings. The task consisted of 80 pictures of living and non-living images, which the volunteers were instructed to categorize while rTMS pulses were applied.

Results: The highest error rates for all errors of all subjects were observed in the left hemisphere´s posterior middle frontal gyrus (pMFG) with an error rate of 60%, as well as in the right hemisphere´s pMFG and posterior supramarginal gyrus with a 45% error rate each. In total the categorization of non-living objects elicited more errors over both hemispheres than the recognition of living objects.

Conclusion: rTMS seems feasible for the detection of categorization function. Moreover, the observed bihemispheric representation, as well as the higher error incidence for the categorization of non-living objects is well in accordance with current literature. Clinical applicability for preoperative mapping in brain tumor patients has to be evaluated as the next step.