Abstract and Keywords
Epilepsy is a neurological condition that enables systematic study of language organization and reorganization. Although the vast majority of healthy individuals are left-hemisphere dominant for language, people with epilepsy are more likely to have atypical language organization. This chapter reviews two general mechanisms of language plasticity, including reorganization due to chronic functional disruption giving rise to slowly progressive structural disturbances from ongoing epileptic activity, as well as acute changes that occur after epilepsy surgery. Evidence is presented from classic “disruption” techniques, such as Wada testing and electrocortical stimulation mapping (ESM), and alternative “activation” techniques, such as functional magnetic resonance imaging (fMRI). Additional findings are is also reviewed from more advanced imaging, specifically diffusion tensor imaging (DTI), reflecting changes in the structure of language circuits pre- and postoperatively. These methods have been used to investigate clinical factors that influence the lateralization and localization of language regions in epilepsy—including but not limited to the location of seizure foci, age of seizure onset, presence of lesions, and extent of abnormal EEG activity between seizures—all of which may be associated with both inter- and intra-hemispheric changes in language networks. The process of language organization and reorganization is complex and heterogeneous, and there are multiple patient variables that can affect results from these different, yet complementary, techniques. For this reason, it is important to understand these issues to optimize clinical care, especially when definitive identification of language cortex is required for surgical planning among patients with refractory epilepsy.
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