Electrocorticographic Analysis of Phonological and Lexical Processing

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DESCRIPTION (provided by applicant): The spatiotemporal dynamics of cortical activity underlying speech perception and production are not well delineated. Current neuroimaging techniques such as fMRI and PET provide high spatial resolution but lack sufficient temporal resolution to address the temporal dynamics of language. In contrast, electrophysiological techniques such as EEG and MEG offer high temporal resolution but lack the spatial resolution needed to ascertain what cortical networks are critically involved in speech perception and production. This proposal aims to address this gap in the literature by analyzing electrical signals with both high temporal resolution and excellent spatial resolution acquired during language processing tasks. The experiments involve recording electrocorticogrpahic activity (ECoG) directly from the cortex of patients undergoing treatment for refractory epilepsy. Multiple electrode grids are neurosurgically placed on the surface of the brain providing extensive coverage of left perisylvian language cortices. The high fidelity ECoG signal contains a rich spectrum of information. In addition to classical event related potential (ERP) analysis, time- frequency analysis techniques offer a window into local and global network connectivity. We will use the recently described high gamma oscillatory response (HG: 60-200 Hz) together with other frequency bands and ERPs as cortical markers for neural activity. We will employ two tasks aimed at elucidating the spatiotemporal dynamics of basic phonological and lexical processing. One task will consist of hearing auditorily-presented phonemes and then re-producing them while the other will use words in the same experimental structure. Comparing the two tasks will serve as a basis for ascertaining the timing dynamics of cortical regions involved in phonological and lexical processing. Furthermore, we will examine the role of the inferior frontal gyrus (IFG) in receptive processing. Specifically, we will address the controversial role of IFG in phonological processing. In addition to providing data relevant to linguistic theory, determining the spatial and temporal dynamics of language processing may lead to advances in public health. New brain mapping techniques may permit shorter and safer procedures during neurosurgery for several disorders (i.e. epilepsy, tumor resection) replacing the traditional cortical stimulation mapping with its associated morbidity related to seizure induction and length of the mapping procedure. PUBLIC HEALTH RELEVANCE: This proposal will help create a cortical map of where and when different brain regions are active during comprehension and production of language. This will expand current theories of how the brain processes language as well provides new brain mapping techniques. Such mapping techniques may permit shorter and safer procedures during neurosurgery for several disorders (i.e. epilepsy, tumor resection) replacing the traditional cortical stimulation mapping with its associated morbidity related to seizure induction and length of the mapping procedure.