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Timothy M. Ellmore, Michael S. Beauchamp, Thomas J. O'Neill, Stephen Dreyer and Nitin Tandon

Object

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.

Methods

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.

Results

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.

Conclusions

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.

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Mario F. Dulay, Dona K. Murphey, Ping Sun, Yadin B. David, John H. R. Maunsell, Michael S. Beauchamp and Daniel Yoshor

Cortical mapping with electrical stimulation (ES) in neurosurgical patients typically involves the manually controlled delivery of suprathreshold electrical current to a discrete area of the brain. Limited numbers of trials and imprecise current delivery methods increase the variability of the behavioral response and make it difficult to collect quantitative mapping data, which is especially important in research studies of human cortical function.

To overcome these limitations, the authors developed a method for computer-controlled delivery of defined electrical current to implanted intracranial electrodes. They demonstrate that stimulation can be time locked to a behavioral task to rapidly and systematically measure the detection threshold for ES in human visual cortex over many trials.

Computer-controlled ES is well suited for the systematic and quantitative study of the function of virtually any region of cerebral cortex. It may be especially useful for studying human cortical regions that are not well characterized and for verifying the presence of stimulation-evoked percepts that are difficult to objectively confirm.