Development of white matter and reading skills

White matter tissue properties are highly correlated with reading proficiency;wewould like to have amodel that relates the dynamics of an individual's white matter development to their acquisition of skilled reading. The development of cerebral white matter involves multiple biological processes, and the balance between these processes differs between individuals. Cross-sectionalmeasures ofwhite matter mask the interplay between these processes and their connection to an individual's cognitive development. Hence, we performed a longitudinal study to measure white-matter development (diffusion-weighted imaging) and reading development (behavioral testing) in individual children (age 7-15 y). The pattern ofwhite-matter development differed significantly among children. In the left arcuate and left inferior longitudinal fasciculus, children with above-average reading skills initially had low fractional anisotropy (FA) that increased over the 3-y period,whereas children with belowaverage reading skills had higher initial FA that declined over time. We describe a dual-processmodel ofwhitematter development comprising biological processes with opposing effects on FA, such as axonal myelination and pruning, to explain the pattern of results.