Presurgical localization of language regions and their networks

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Book Chapter

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MEG language-evoked fields (LEFs) are reliably used for detecting the dominant hemisphere of language processing. This laterality measure is based on the accurate localization of Broca’s and Wernicke’s activated areas during language processing. There are several tasks ranging from semantic decision-making, verb generation, and picture naming to auditory word presentation that have been used with success. These tasks can be expressive (where Broca’s activity is strongly activated) or receptive (where Wernicke’s is strongly activated). In the general population, most right-handed individuals are left hemispheric dominant for language. Patients requiring surgical resection will have language mapping performed, so the surgeon can be aware that there may be displacement of either or both Broca’s and Wernicke’s language processing areas near the planned resection site. Since epilepsy may disrupt only Broca’s or only Wernicke’s networks, it is wise to map both expressive and receptive language processing. The use of MEG neuroimaging techniques is needed to reliably predict altered language networks in patients and to provide definitive identification of language eloquent cortices for localization and lateralization necessary for clinical care.

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