Cortical Localization in Temporal Lobe Epilepsy

Columbia University Health Sciences, New York NY

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Abstract

DESCRIPTION (provided by applicant): Temporal lobe resection offers the best hope of cure for patients who suffer from refractory temporal lobe epilepsy. Unfortunately, this surgery often comes with a cost to naming ability, which is typically already compromised before surgery. Identification of naming deficits prior to surgery provides valuable information that can lateralize seizure onset. Furthermore, sparing of naming cortex identified via stimulation mapping helps prevent naming decline postoperatively. Historically, visual object naming has been the sole method both for assessing naming and for stimulation mapping to identify essential language cortex. However, visual naming has failed to reliably identify true naming deficits and has failed to consistently protect postoperative naming. The recent addition of auditory description naming has enhanced our ability to lateralize and localize cortical dysfunction associated with epileptogenic cortex. In stimulation mapping, auditory naming has improved mapping efficacy by identifying clinically relevant language cortex that otherwise would have remained undetected. Despite these considerable advances, two problems persist. First, some patients still exhibit postoperative naming decline and second, the work in auditory naming has not been extended to children. These two issues will be addressed in the two subcomponents of the proposed project: Adult Mapping and Child Naming. Regarding Adult Mapping, preliminary studies suggest two new potential sources of naming decline: 1) Hippocampal removal (the hippocampus is generally considered a memory structure without language involvement, but recent postoperative and imaging data implicate it in naming decline) and 2) Surgical disruption of lateral temporal areas that support naming-related linguistic functions (pilot mapping results reveal anatomically distinct sites that mediate semantic and phonological access, both of which are necessary for naming). To address these two possibilities, the linguistic processes that comprise naming will be tested during direct stimulation of hippocampal and lateral temporal sites to establish the role and clinical relevance of these brain areas in naming. Project goals for Adult Mapping are to determine: a) Which aspects of naming are mediated by the hippocampus, b) Whether "non-naming" lateral temporal sites mediate critical naming sub-processes, and c) Whether the nature and severity of naming decline are related to the location, type, or number of naming sites disrupted by surgery. Regarding Child Naming, we will address the absence of age appropriate naming measures for children with epilepsy. Project goals for this component of the project are to: a) Develop and standardize analogous pediatric versions of the adult auditory and visual naming tests via normative study and patient testing, and b) Determine whether auditory naming performance predicts hemispheric lateralization of seizure onset in children with lateralized epilepsy, as it does in adults. Results from the overall project promise new insights into temporal lobe organization of language, better prediction and prevention of postoperative deficits, and improvements in pediatric epilepsy care. PUBLIC HEALTH RELEVANCE: This work will lead to better understanding of temporal lobe language organization, which will improve our ability to preserve language abilities in individuals who require temporal lobe epilepsy surgery. This work will also provide a means for assessing and understanding word finding ability in children.