Neural Development of Lexical Processing

Northwestern University, Evanston IL

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Abstract

[unreadable] DESCRIPTION (provided by applicant): Over the past several years, we have formulated a developmental neuro-cognitive model of lexical processing in normal readers based on cross-sectional functional magnetic resonance imaging (fMRI) data and we have collected our first longitudinal data on these children 2 years after their initial assessment. The proposed grant will longitudinally follow normal children (7- to 17-year-olds) and children with reading disorders (11- to 15-year-olds) when they perform a variety of lexical tasks. These tasks will include orthographic (spelling), phonological (rhyming) and semantic (meaning) judgments in the visual and auditory modalities. Not only is this proposal innovative because we use a variety of lexical tasks, but we also have multiple perceptual controls and multiple parametric manipulations of difficulty so we can more effectively examine developmental and group effects specific to lexical processing. The aim of this study is to determine whether different groups have different developmental trajectories. A longitudinal design is crucial to rule out cohort effects and to examine the predictability of the individual's subsequent brain development from their earlier reading skill and brain activation patterns. To our knowledge, only two studies have used a longitudinal design to examine neural changes over development. In addition to examining whether higher and lower skill normal readers have different developmental trajectories, we will examine whether dyslexic children with specific deficits in decoding orthographic stimuli have different developmental trajectories from language-impaired children with deficits in decoding orthographic stimuli in addition to general language processing deficit. We will also compare the children with disorders to age-match versus reading-match normal readers to address the question of developmental delay versus deviance. Our general hypothesis is that individual differences in brain activation between readers will increase with age. This will be tested using hierarchical linear modeling to examine growth curves in the rate of change (e.g. slope) and in the shape of change (e.g. acceleration). We will use this technique to look at developmental changes in signal intensity in our critical regions of interest, but also for changes in effective connectivity using Dynamic Causal Modeling. This analysis procedure allows the assessment of the directional influence of one brain region on another. This proposal will give us basic information about how the brain changes throughout childhood and adolescence, but also how the brains of children with reading disorders differ in their development. This grant has implications for diagnosis and intervention in children with reading and language problems [unreadable] [unreadable] [unreadable]