Temporal-callosal pathway diffusivity predicts phonological skills in children

Abstract

The development of skilled reading requires efficient communication between distributed brain regions. By using diffusion tensor imaging, we assessed the interhemispheric connections in a group of children with a wide range of reading abilities. We segmented the callosal fibers into regions based on their likely cortical projection zones, and we measured diffusion properties in these segmented regions. Phonological awareness (a key factor in reading acquisition) was positively correlated with diffusivity perpendicular to the main axis of the callosal fibers that connect the temporal lobes. These results could be explained by several physiological properties. For example, good readers may have fewer but larger axons connecting left and right temporal lobes, or their axon membranes in these regions may be more permeable than the membranes of poor readers. These measurements are consistent with previous work suggesting that good readers have reduced interhemispheric connectivity and are better at processing rapidly changing visual and auditory stimuli.corpus callosum ͉ diffusion tensor imaging ͉ magnetic resonance imaging ͉ reading R eading is a crucial skill in modern industrialized societies. Therefore, it is important to understand how people learn, or fail to learn, this skill. A substantial behavioral and neuroscience literature characterizes the neural basis of reading in both children and adults. Functional neuroimaging studies of reading have identified a distributed functional network where neural activity correlates with reading skill (1-5).Such a distributed network of cortical regions requires a set of long-range white matter tracts to communicate essential signals. Structural neuroimaging studies using diffusion tensor imaging (DTI) have identified white matter properties that vary with reading skill. Klingberg et al. (6) were the first to apply DTI in the study of reading disabilities. They compared fractional anisotropy (FA) (a measure of the diffusion anisotropy within the white matter) in reading-impaired and normal-reading adults. They found a statistically significant difference primarily in a left temporal-parietal region of the white matter. This basic result has been replicated and extended to children by three independent groups (7-9).In addition to these recent measurements of the white matter using DTI, there is also a long history of measurements and theories arguing for a relationship between interhemispheric communication and reading (10-15). Orton (10) proposed that the lack of lefthemisphere language dominance was the cause of dyslexia. Geschwind and colleagues (11, 16) also argued that reduced left-hemisphere dominance was a cause of dyslexia. More recent measurements using structural MRI suggest that the corpus callosum has a different shape in dyslexic adults compared with those with normal reading development (17-19). Other research on the callosum supports the basic idea that increased functional (20) and structural (21) hemispheric asymmetry is associated with sparser interhemis...

Brain Volume Reductions within Multiple Cognitive Systems in Male Preterm Children at Age Twelve

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Distinguishing cause from effect – many deficits associated with developmental dyslexia may be a consequence of reduced and suboptimal reading experience

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The impact of asymmetrical light input on cerebral hemispheric specialization and interhemispheric cooperation

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