Transcranial magnetic stimulation: Language function

Studies of language using transcranial magnetic stimulation (TMS) have focu sed both on identification of language areas and on elucidation of function . TMS may result in either inhibition or facilitation of language processes and may operate directly at a presumptive site of language cortex or indir ectly through intracortical networks. TMS has been used to create reversibl e "temporary lesions," similar to those produced by Wada tests and direct c ortical electrical stimulation, in cerebral cortical areas subserving langu age function. Rapid-rate TMS over the left inferior frontal region blocks s peech output in most subjects. However, the results are not those predicted from classic models of language organization. Speech arrest is obtained mo st easily over facial motor cortex, and true aphasia is rare, whereas right hemisphere or bilateral lateralization is unexpectedly prominent. A clinic al role for these techniques is not yet fully established. Interfering with language comprehension and verbal memory is currently more difficult than blocking speech output, but numerous TMS studies have demonstrated facilita tion of language-related tasks, including oral word association, story reca ll, digit span, and picture naming. Conversely, speech output also facilita tes motor responses to TMS in the dominant hemisphere. Such new and often-u nexpected findings may provide important insights into the organization of language.