BRAIN ASYMMETRY AND LANGUAGE DEVELOPMENT

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The human brain is functionally and anatomically lateralized. In most adults, language is localized in the left hemisphere while spatial and emotional functions are localized in the right hemisphere. Leftward asymmetry of the planum temporale (Wernicke's area) and pars triangularis (Broca's area) are believed to be the neurobiological substrate of this functional lateralization. During childhood, functional lateralization becomes irreversible. Pilot data in 40 normal children suggest that developmental changes in cerebral asymmetry occur during this period. This project seeks to confirm those changes and to explore the relation between asymmetry and the development of language skills. The study will provide a data base of measurements of normal cerebral morphology as visualized in the magnetic resonance imaging (MRI) scans of children between the ages of 5 and 10. The major objectives are to determine whether (1) volumetric asymmetries of the anterior and posterior language regions change during this period; (2) planar asymmetry predicts skill in phonemic awareness, reading and spelling; and (3) pars triangularis asymmetry predicts skills in expressive oral language and fluency. In addition, volumetric changes in structures not thought to be primarily involved in language development -- the corpus callosum, caudate nucleus and the hippocampus, will be measured to examine the specificity of the findings. A group of 100 subjects, aged 5 years 6 months to 7 years 6 months, with normal IQs, will be given a language history questionnaire and a neurolinguistic battery including tests of phonemic awareness, reading and oral language. The subject group will be balanced for sex and handedness. The subjects will receive MRI scan of the head that provides a gapless series of thin sagittal sections. Computer based volumetric measurements will be made of the planum temporale in Wernicke's area, pars triangularis in Broca's area, the hippocampus, and the caudate nucleus. The cross- sectional area of the genu, body, isthmus, and splenium of the corpus callosum and the total intracranial volume will also be measured. The children will be tested and scanned again two years later. Based on previous work as well as pilot data it is predicted (1) that increases in leftward asymmetry of the planum temporale will accompany developmental improvements in phonemic awareness, reading and spelling; (2) dextral children will have greater leftward asymmetry of pars triangularis than adextrals; (3) children with good expressive skills will have greater asymmetry of pars triangularis. The results should shed light on the neuronal substrate of normal language development in childhood and provide a normal database from which comparisons to brain structures in language and learning impaired children can be made. The data will also enable the accurate mapping of language areas for correlation with EEG and other functional studies in children.