[Language mapping with direct electrical stimulation].

Language mapping with electrical stimulation in patients with lesions close to the language area aids surgery by identifying the language area in each individual. This method is quite important in a clinical setting, and is the most reliable for preventing persistent language deficits after resection. Furthermore, language mapping with electrical stimulation has revealed that the functional organization of the language area is more complex than previously suggested by functional MRI and other methods. The language-related sites where electrical stimulation induced abnormality during language tasks were spatially distinct and surprisingly varied amona patients. In addition, electrical stimulation revealed a mosaic of language function, in which sites even 5-10 mm apart were functionally distinct. Cortical sites specifically related to a language function e.g., repetition, were surrounded by sites related to another language function but not to repetition. These findings suggested that the "language area" is not spatially homogeneous over centimeters of the cortex, but consists of functional sub-regions of the cortex. Findings obtained using intraoperative electrical stimulation of the subcortical white matter have supported the dual language pathways-the dorsal and ventral pathways. Electrical stimulation of the arcuate fasciculus induced phonological paraphasia and that of the inferior occipitofrontal fasciculus induced semantic paraphasia. However, no language deficits were induced by stimulation of the inferior longitudinal fasciculus, thereby indicating the indirect role of this bundle in language function. Our current models of human language organization can be modified on the basis of language mapping with electrical stimulation.