Age and reading ability shape white matter development across the lifespan: A cross-sectional study.

Reading is supported by neural systems that change across the lifespan, yet the development of reading-related white matter remains underexplored, particularly in non-alphabetic writing systems. This cross-sectional study examined white matter-reading associations in 126 Mandarin Chinese readers aged 7 to 77 years. Diffusion tensor imaging quantified fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD), and radial diffusivity (RD) in seven pairs of bilateral reading-related tracts: the arcuate fasciculus (AF), superior longitudinal fasciculus (SLF I, II, and III), inferior fronto-occipital fasciculus (IFOF), inferior longitudinal fasciculus (ILF), and uncinate fasciculus (UF). Most tracts showed nonlinear age-related trajectories, with FA generally following an inverted U-shaped pattern and MD, AD, and RD showing opposite U-shaped patterns; by contrast, FA in the left ILF and right UF increased linearly with age. In addition, word reading efficiency was positively associated with FA in the bilateral AF, bilateral SLF III, and right SLF II. These FA effects were accompanied by lower RD across all significant tracts and lower MD in the right-hemisphere tracts. Sentence reading fluency showed a more limited association with FA, mainly involving the right AF. Further, age moderated the association between word reading efficiency and FA in the right AF and right SLF II: better word reading fluency predicted higher FA at younger ages, whereas the association became weak in adulthood and negative at older ages. These findings reveal heterogeneous maturation of reading-related white matter pathways and highlight both stable and age-dependent structural correlates of reading fluency across the lifespan in Chinese readers.