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NBS reveals language shift from the left to right hemisphere in patients with language-eloquent brain tumors

30 September 2013

Two separate studies recently published

HELSINKI, Finland—Sept. 30, 2013--Clinicians at the Department of Neurosurgery; Klinikum rechts der Isar, Technische Universität München, Germany, have shown that if regions of the brain involved in language in the language-dominant hemisphere are damaged, language processing can shift to the opposite hemisphere. 

15 patients who had undergone brain surgery for tumor participated in the study that used the NBS System with the NexSpeech module. NBS speech mapping works by using rTMS to create temporary, highly-localized virtual lesions which can interfere with language function. Because the 15 patients had undergone direct cortical mapping during awake surgery, they were all confirmed to have had language lateralization on the left-side. After recovery from surgery, the clinicians used the NBS System to identify cortical regions that are essential in language and not only in speech processing. In these 15 patients they were able to show that NBS mapping of corresponding right cortical regions caused a range of errors, especially no response and performance errors. The clinicians concluded that lesions within language-eloquent brain had induced plasticity, which resulted in a shift of language function to the non-dominant right hemisphere. 

These findings support earlier data from fMRI-based investigations. However, this study is the first lesion-based study that actually proves language plasticity as a shift to the non-dominant hemisphere by an anatomically traceable method. The clinical implications of these findings may be significant. If NBS is able to reliably measure the degree of language shift in brain tumor patients, it may be able to perform more extensive tumor resection within perisylvian language regions - relying on brain plasticity to preserve language function. A surgical technique which exploits plasticity to preserve motor function has already been shown to be feasible in the treatment of low-grade gliomas. 

In a separate paper, clinicians at the Department of Neurosurgery, Charité University Hospital, Berlin studied 15 right-handed healthy volunteers and 50 right-handed consecutive patients with left-sided gliomas using the NBS system with rTMS. In healthy subjects, language disturbances were almost exclusively induced in the left hemisphere, as expected. However, in the brain tumor patients language errors were not only more frequent, but also induced at a similar ratio over both left and right hemispheres. The authors conclude that the increased sensitivity of the right hemisphere to rTMS disturbance, suggests reorganization of language representation in brain tumor patients.

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