gms | German Medical Science

Objective: Non-invasive language mapping is commonly facilitated via two different approaches, functional magnet resonance tomography (fMRI) and navigated transcranial magnetic stimulation (nTMS). The aim of our examination was to further highlight similarities and differences of both methods in regard to hemispheric dominance and the anatomical areas evoked during language mapping.

Methods: Since 2015, 23 patients received both, fMRI and nTMS language mapping in our facility. fMRI was performed using a 3 tesla MRI scanner and a blood oxygenation desaturation (BOLD) protocol applying a word pairing task. nTMS was performed with 100-130% of resting motor threshold (RMT) while using a picture naming task for language mapping. Hemispheric dominance for fMRI and nTMS was defined according to activation/response predominance between hemispheres. We compared the results using sign test. For a detailed comparison, we used a cortical parcellation and correlated activation of each gyrus. Statistical analysis was performed using Spearman's rank correlation coefficient.

Results: 15 male and 8 female patients were enrolled in this study. The calculated error rate (ER, evoked error per stimulation trail) was 10,0% (± 0.09) for the left and 10.1% (± 0.10) for the right hemisphere.In 66.7% of examinations, fMRI and nTMS predicted the same hemispheric dominance, this is confirmed by the sign test (p=0.63). However, correlation of anatomical areas with speech relevance between the two methods was poor. The best correlation between fMRI an nTMS for the right hemisphere was found for anterior superior temporal gyrus (aSTG) with a correlation coefficient of 0.57 (p=0.04). Best correlation on the left hemisphere was found in superior parietal lobe (SPL) with a correlation coefficient of 0.41 (p=0.06).

Conclusion: Our findings suggest that fMRI and nTMS lead to comparable results in determining hemisphereic dominance, however they do not deliver the same results in predicting language relevant areas in detail. This might be due to the fundamentally different functional principles of both examinations. Literature suggests that both methods can help surgeons get an idea of the patient’s language function and positively influence eloquent tumor resection when used for preoperative planning. We recommend relying on the method you are most accustomed to.