The overall objective of this project is to examine the neural substrate of normal and aberrent language development using noninvasive electrophysiologic and neuroimaging methods for dynamic localization of brain activity associated with auditory and linguistic processing. These studies will examine the temporal sequencing of electrical activity within the brain structures involved in normal language processes during early development. These normative data provide a basis for examining deviant language development in children with central auditory processing impairment. To delineate the brain regions involved in specific auditory and linguistic processes in individual subjects we combine detailed Laplacian mapping of surface recorded event related brain potentials (ERPs) with noninvasive localization of their intracerebral generators, using Brain Electrical Source Analysis (BESA) in conjunction with magnetic resonance imaging (MRI). The BESA/MRI colocalization technique has been developed during the current project period to complement the Laplacian topographic analyses. Our major concern is with the receptive processing of human speech sounds in children with normal language development and in language-impaired children with normal peripheral and subcortical auditory function, since the adequate processing of complex acoustic stimuli is a necessary condition for the normal development of language, including phonology, lexical and semantic competance. The project period will (1) define normative patterns of brain electrical source localization and temporal patterns of cortical activation in children between the ages of six and ten years using Laplacian topographic analyses and the BESA/MRI colocalization method. These studies will employ a chronometric approach, in which the acoustic cues in auditory and linguistic tasks will be carefully timed. This will enable us to maximize the possibilities for identifying the cerebral substrate of specific linquistic processes, by examining both the temporal and spatial differentiation of brain activity associated with acoustic, phonological, lexical and semantic processing tasks, and (2) identify aberrent patterns of brain activity in individual children who exhibit specific central auditory and receptive language deficits, including children with impairment of phonemic and/or verbal processing alone or in combination with other language deficits.
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