Journal Article

Early childhood development of white matter fiber density and morphology

Cho, Ivy, Dhollander, Thijs, Dimond, Dennis, Rohr, Christiane S., Connelly, Alan, Bray, Signe, Smith, Robert E., Lebel, Catherine, Dewey, Deborah

2020

Overview

Early childhood is an important period for cognitive and brain development, though white matter changes specific to this period remain understudied. Here we utilize a novel analytic approach to quantify and track developmental changes in white matter micro- and macro-structure, calculated from individually oriented fiber-bundle populations, termed “fixels”. Fixel-based analysis and mixed-effects models were used to assess tract-wise changes in fiber density and bundle morphology in 73 girls scanned at baseline (ages 4.09–7.02, mean ​= ​5.47, SD ​= ​0.81), 6-month (N ​= ​7), and one-year follow-up (N ​= ​42). For comparison, we also assessed changes in commonly utilized diffusion tensor metrics: fractional anisotropy (FA), and mean, radial and axial diffusivity (MD, RD, AD). Maturational increases in fixel-metrics were seen in most major white matter tracts, with the most rapid increases in the corticospinal tract and slowest or non-significant increases in the genu of the corpus callosum and uncinate fasciculi. As expected, we observed developmental increases in FA and decreases in MD, RD and AD, though percent changes were smaller relative to fixel-metrics. The majority of tracts showed more substantial morphological than microstructural changes. These findings highlight early childhood as a period of dynamic white matter maturation, characterized by large increases in macroscopic fiber bundle size, mild changes in axonal density, and parallel, albeit less substantial, changes in diffusion tensor metrics. •White matter fiber density and bundle size increase with age in early childhood.•Increases in fiber density and bundle size occur in most major white matter tracts.•Rate of change is fastest in the corticospinal tract and slowest in frontal tracts.•Increases in fiber bundle size are more substantial than increases in fiber density.•These changes are more substantial than changes in diffusion tensor metrics.

• Publisher: Elsevier Inc,Elsevier Limited,Elsevier
• Subject: Age / Anisotropy / Child / Child development / Child Development - physiology / Child, Preschool / Childhood / Children / Cognitive ability / Corpus callosum / Diffusion Tensor Imaging - methods / Early childhood / Female / Fiber bundle morphology / Fiber density / Fixel-based analysis / Follow-Up Studies / Genetic disorders / Humans / Magnetic resonance imaging / Morphology / Nerve Fibers / Neural Pathways - anatomy & histology / Neural Pathways - diagnostic imaging / Neural Pathways - growth & development / Pyramidal tracts / Pyramidal Tracts - anatomy & histology / Pyramidal Tracts - diagnostic imaging / Pyramidal Tracts - growth & development / Scanners / Studies / Substantia alba / White matter / White Matter - anatomy & histology / White Matter - diagnostic imaging / White Matter - growth & development