Functional differentiation between the left and right hemisphere for a sub-region of Wernicke's area is revealed with fMRI-guided, single-pulse TMS

During the past two decades, studies of neural organization have been bolstered by the addition of functional and structural brain-imaging techniques capable of localizing and correlating brain activity to cognitive functions. With potential clinical applications abound, localizing language-related activity prior to neurosurgery is an interest shared by both neuroscientists and neuroradiologists who are interested in protecting essential language regions in neurosurgery candidates. Since imaging is correlative, however, it does not distinguish essential brain activity from supporting and associated activity and therefore cannot be used independently to determine hemispheric language dominance. Transcranial magnetic stimulation (TMS), on the other hand, is a non-invasive technique that stimulates targeted brain regions directly and can therefore inform causative structure/function relationships.;The goal of this study is to develop non-invasive techniques that definitively identify hemispheric language dominance. Functional Magnetic Resonance Imaging (fMRI) was used to locate language-related regions in 36 right-handed participants. In most participants, there were two clusters of activation within classic Wernicke's territory. We termed these dorsal and ventral Wernicke's areas. On a separate day, fourteen of the thirty-six participants returned to participate in a single-pulse TMS experiment which targeted dorsal and ventral Wernicke's areas and their right-sided homologues. Picture naming latency was decreased following TMS of left-sided dorsal and ventral Wernicke's areas as well as right-sided ventral Wernicke's homologue. No effect was observed following TMS of dorsal Wernicke's homologue.;These results highlight the advantages of using cross-modal imaging techniques by providing direct evidence in support of modern theories of neural language organization that propose a bilateral sub-region of Wernicke's area involved in phonological processing, and a unilateral left-sided component involved in integration and relay of semantic information to other cortical regions.