This is a study of the functional and neuroanatomical architecture of language processes based on the reversible impairments produced by direct electrical cortical stimulation. Current neuropsychologic and neuroanatomic models all posit that language abilities are mediated by smaller, distinct processing components with specific interconnections. Some of these models specify the neuroanatomic loci of these components. The bulk of their evidence has been derived from studies of patients with fixed lesions and stable language impairments. However, this source has been part of the reason why these models have proven to be difficult to test adequately: Accidentally placed, relatively large, irreversible lesions make it difficult to fractionate the deficits that are actually present, or the true role that is played by those functions that remain. Direct, focal, electrical cortical stimulation has demonstrated the potential for overcoming some of these difficulties by being able to induce multiple, selective impairments of functions with complete reversibility. Accordingly, we will investigate the structure of reading, visual confrontation naming, and auditory comprehension through stimulation-induced deficits. Studies of static deficits on these tasks have proven to be very productive despite their limitations, and therefore should be particularly informative when deficits can be induced reversibly, and when different patterns of deficits can be produced in the same subject at different sites. Subjects will be patients with subdural electrode arrays implanted over the peri-Sylvian language regions, for clinical localization purposes prior to cortical resection for epilepsy or tumor. The first part of this study will seek to determine the nature of the deficit caused by stimulation, and establish optimal stimulation parameters. The second part will be single case studies of deficits found on clinical testing, to establish: (1) what components subserving task performance are impaired, (2) how these components are interrelated and (3) whether these relationships are the ones predicted by current theory or whether alternative representational or processing models are necessary. The third part of this proposal will relate the data on component impairments at specific cortical stimulation sites to cortical maps, by patient and by patient group. These data will therefore make a unique contribution to scientific and medical knowledge of language processes and of their cortical representations.
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