The growth pattern of white-matter tracts in the brain is highly correlated with reading ability. Literacy requires the integration of activity in brain areas involved in vision, hearing and language. Efficient communication between these areas is essential for proficient reading.
In this report, white matter development (diffusion-weighted imaging) and reading development were studied in children (ages 7 to 12 years) over a three-year period. There were big differences in reading ability between the children which persisted over time. Children who were weak readers relative to peers at the beginning of the study were still weak three years later.
Differences in the growth of the arcuate fasciculus and inferior longitudinal fasciculus white-matter tracts could predict the variations in reading ability. Strong readers started off with a low fractional anisotropy signal in both tracts on the left side of the brain, which got stronger over the three year study period. Weaker readers exhibited the opposite pattern.
The authors propose a model of white matter development influenced by axonal myelination and pruning, to explain the results. Pruning and myelination of nerve fiber connections are both influenced by experience. Underused fibers are pruned, whereas others are myelinated. These processes occur at different rates and times in different people. In poor readers, the two processes may be out of sync, compared to the situation in good readers where both processes may develop together at an even rate. Individual children may benefit from reading lessons that are tailored to their patterns of brain development. For example, it is hypothesized that children may find it easiest to learn to read at certain stages of brain development, when there is greater potential for remodeling in the brain.
Yeatman JD, Dougherty RF, Ben-Shachar M and Wandell BA: Development of white matter and reading skills. Proc. Natl. Acad. Sci. USA [Epub ahead of print, October 8, 2012; doi: 10.1073/pnas.1206792109 ].