Fiber-Specific Structural Properties Relate to Reading Skills in Children and Adolescents

Abstract

Recent studies suggest that the cross-sectional relationship between reading skills and white matter microstructure, as indexed by fractional anisotropy, is not as robust as previously thought. Fixel-based analyses yield fiber-specific micro- and macrostructural measures, overcoming several shortcomings of traditional DTI approaches. We ran a whole-brain analysis investigating whether fixel-derived metrics related to single-word reading skills in a large, open, quality-controlled data set of 983 children and adolescents ages 6-18. We also compared fixel metrics between participants with (n = 102) and without (n = 570) reading disabilities. We found that the product of fiber density (FD) and cross-section (FC), or FDC, positively related to reading skills throughout the brain, especially in left temporoparietal and cerebellar white matter, but did not differ between groups. Exploratory analyses revealed that among metrics from other diffusion models - DTI, DKI, and NODDI - only orientation dispersion index (ODI) from NODDI was associated (inversely) with reading skills. Our findings further support the importance of left-hemisphere dorsal temporoparietal white matter tracts in reading. Additionally, our results suggest future DWI studies of reading should be designed to benefit from advanced diffusion models, include cerebellar coverage, and consider continuous analyses that account for individual differences in reading skill.