Influences of the early family environment and long-term vocabulary development on the structure of white matter pathways: A longitudinal investigation

In the present longitudinal study, we investigated the joint effect of early family factors and long-term vocabulary development on the structure of reading-related white matter pathways in adolescents. Seventy-nine children participated in this study. Family environment was measured via parental questionnaire between age 1 and age 3. From age 4 to age 10, children's vocabulary skills were tested annually. At age 14, diffusion tensor imaging data of the children were collected. Using individual-based tractography, 10 reading-related tracts of the two hemispheres were delineated. Different family factors were found to be correlated with different pathways: Age of literacy exposure was correlated with fractional anisotropy of the direct segment of the left arcuate fasciculus, while an association trend was found between early family socioeconomic status and fractional anisotropy of the left inferior frontal occipital fasciculus. Further regression analyses showed that the age of literacy exposure modulated the relationships between vocabulary development and the structure of the left arcuate fasciculus. Specifically, in the earlier literacy exposure group, no association was found between vocabulary development and the strength of the arcuate fasciculus, whereas in the later literacy exposure group, significant associations were found between vocabulary development and the strength of the arcuate fasciculus.