Article
Language fiber tracking using repetitive navigated transcranial magnetic stimulation combined with a hemispheric dominance ratio
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Published: | June 2, 2015 |
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Objective: Cortical stimulation by repetitive navigated transcranial magnetic stimulation (rTMS) can be used for bihemispheric language mapping in brain tumor patients. When regions of interests (ROIs) are created based on the corresponding mapping results of both hemispheres, fiber tracking using these individual rTMS language maps principally allows for detection of interhemispheric connectivity.
Method: We enrolled 36 patients with left-sided language eloquently located brain lesions, who underwent preoperative language mapping by rTMS of both hemispheres combined with an object naming task. Naming errors due to stimulation were identified, and the corresponding cortical spots were used to create ROIs. Then, fibers connecting the rTMS-based ROIs of both hemispheres were tracked (fiber length: 40 mm, fractional anisotropy: 0.01) in the preoperative diffusion tensor imaging (DTI) sequences. In addition naming error rates were used to calculate individual hemispheric dominance ratios (= HDRs: left-hemispheric naming error rate divided by the right-hemispheric error rate) for patients with and without interhemispheric connectivity separately.
Results: In summary fibers connecting rTMS-based ROIs of both hemispheres were detectable in 12 patients (33%). Concerning the group of patients in which interhemispheric connectivity was found, the HDR was 1.5 ± 0.7 (range: 0.6 - 2.9), while it was 1.7 ± 1.4 (range: 0.1 - 6.0) in patients without any detectable interhemispheric fibers. Comparing the mean HDR values of both groups, there was no statistically significant difference (p>0.05).
Conclusions: In general, cortical language spots identified by rTMS can be used for the identification of interhemispheric connectivity in brain tumor patients. However, we were not able to find any correlation between cortical language dominance and subcortical interhemispheric connectivity.