Callosal pathways associated with reading and phonological awareness in children
RF Dougherty, GK Deutsch, M Ben-Shachar, P Potanina,
R Bammer and BA Wandell
Methods: We used DTI to measure fractional anisotropy (FA) in 54 children aged 7 to 12. We also measured reading, phonological awareness (PA), and Full-Scale IQ. These scores were compared to FA in four callosal segments: the splenium, isthmus, body and genu/rostrum. These segments were created by manual selection of the corpus callosum in the mid-sagittal plane followed by automated fiber tracking to identify callosal tracts up to 10mm from the mid-sagittal plane.
Results: Of the four callosal segments, only the splenium showed a significant correlation between FA and behavioral measures. Mean FA in the splenium was negatively correlated with all the reading measures and with PA, but not with IQ. Of the reading measures, passage comprehension (r=-0.35, p<0.01) and PA (r=-0.46, p<0.001) were the most strongly correlated with FA. The correlations were strongest near the mid-sagittal plane, but also present in the splenial pathways 10mm to either side.
Conclusion: FA increases with myelination, axon density, axon size and directional coherence. While we cannot disentangle these causes, the results suggest increased hemispheric connectivity between posterior cortical regions in poor readers, perhaps due to a failure to prune these long-range connections. Such an anatomical difference is consistent with imaging results that suggest a less lateralized language system in poor readers.
Support Contributed By: NIH EY-015000