A new study shows that mapping language centers via navigated repetitive transcranial magnetic stimulation (nrTMS) before brain surgery could help improve surgical planning.

Researchers at Nagoya University School of Medicine (Japan) conducted a prospective, non-randomized study involving 61 adult patients (39 men, 22 women; mean age 41.1 years), which included 42 low-grade gliomas and 19 high-grade gliomas. Inclusion criteria included the presence of left- or right-side brain tumors in the vicinity of or inside areas anatomically associated with language functions, and scheduled awake brain surgery. Prior to surgery, rapid nrTMS was applied while the patient named images; when they failed, the language center was detected.

The results showed that the tumor was located in the left hemisphere in 50 (82%) of the patients, and in the right hemisphere in 11 (18%). In the 50 patients with left-side gliomas, the factor that significantly impacted nrTMS mapping accuracy in the language center was tumor involvement; otherwise, nrTMS showed a good degree of reliability. The scientists also successfully used nrTMS to determine the side of the brain where the language center is mainly located in each patient. The study was published on June 3, 2020, in Scientific Reports.

“Subgroup analysis showed that the non-involvement of language-related regions afforded significantly better the area under the curve values than the involvement of language-related regions,” concluded lead author neurosurgeon Kazuya Motomura, MD. “Our findings suggest that nrTMS language mapping could be a reliable method, particularly in obtaining responses for cases without tumor-involvement of classical perisylvian language areas.”

Transcranial magnetic stimulation is a noninvasive method to cause depolarization or hyperpolarization in the neurons of the brain via electromagnetic induction to induce weak electric currents using a rapidly changing magnetic field.

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