The Use of nrTMS Data for Tractography of Language Networks
The prevention of permanent neurological deficits is of prime importance in the surgical treatment of lesions arising in or near eloquent brain regions. In an attempt to minimize the risks, fMRI and diffusion tensor imaging fiber tracking (DTI FT) are routinely used in preoperative assessment. These techniques however rely heavily on mathematical algorithms to interpret and model underlying magnetic resonance datasets, resulting only in an indirect representation of neural activity and interconnections. Transcranial magnetic stimulation (TMS) on the other hand can be used to assess cortical function directly. Navigated repetitive TMS (nrTMS) has already shown promising results in the cortical mapping of language functions. The use of truly functional nrTMS that generated language-specific stimulation points as seed points in DTI FT of language networks, instead of calculated fMRI activation clusters, enhances the spatial resolution of the resulting tractography, providing new insights in the already complex organization of the language system. This information in turn can be integrated into the preoperative workup.
Our gratitude goes to our patients and volunteers, and we thank Sascha Freigang and Dr. Shane Matsune Fresnoza for performing the nrTMS language mappings and Mag. Karla Zaar for the language evaluations. All examinations were performed according to good clinical practice (GCP) guidelines, following protocol approval by the local ethics committee (reference # 28-144 ex 15/16).
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