Relationships between essential cortical language sites and subcortical pathways

Abstract

Maps produced using either electrical stimulation or functional imaging have demonstrated a distributed network of cortical regions involved in expressive and receptive language tasks. The pattern of connectivity among components of this network has begun to be explored with diffusion tensor (DT) imaging, but has yet to be completely characterized. In this study the authors used DT imaging-based tractography to examine the interrelationship between cortical areas found to be essential for language by intraoperative electrical stimulation. The authors localized the arcuate fasciculus (AF), a white matter fiber system connecting frontal and parietotemporal areas in 10 patients, 9 of whom subsequently underwent left hemispheric language mapping. The authors found that 81 (79%) of 102 essential language sites (ELSs) were closely related to the AF. Of all ELSs, 59% were located within 7.5 mm of AF fiber pathway terminations, and another 20% contained pathways terminating closer to the AF than would be expected by chance (p < 0.05). Additionally, direct subcortical stimulation of the AF following focal cerebral resections produced transient language deficits. The close spatial relationship found between ELSs and the AF suggests that tractography data alone may be used for localization of ELSs. The deficits evoked by subcortical stimulation validate and demonstrate the utility of this AF localization technique, and provide further evidence that the AF is an important pathway for fluent language. Taken together, these results demonstrate that DT imaging of the AF may be used to predict the location of brain areas that will be eloquent by the standards of stimulation mapping.