Abstract
The purpose of the present study was to detail the childhood developmental course of different white matter (WM) characteristics. In a longitudinal diffusion tensor imaging (DTI) study of 159 healthy children between 4 and 11years scanned twice, we used tract-based spatial statistics as well as delineation of 15 major WM tracts to characterize the regional pattern of change in fractional anisotropy (FA), mean (MD), radial (RD) and axial diffusivity (AD). We tested whether there were decelerations of change with increasing age globally and tract-wise, and also illustrated change along medial-to-lateral, posterior-to-anterior and inferior-to-superior gradients. We found a significant linear increase in global FA, and decrease in MD and RD over time. For mean AD, a weak decrease was observed. The developmental changes in specific WM tracts showed regional differences. Eight WM tracts showed non-linear development patterns for one or several DTI metrics, with a deceleration in change with age. Sex did not affect change in any DTI metric. Overall, greater rate of change was found in the left hemisphere. Spatially, there was a posterior-to-anterior gradient of change with greater change in frontal regions for all metrics. The current study provides a comprehensive characterization of the regional patters of change in WM microstructure across pre-adolescence childhood.
Highlights
Increase for fractional anisotropy (FA) was especially evident in association tracts (SLF, inferior longitudinal fasciculus (ILF), inferior fronto-occipital fasciculus (IFOF) and uncinate fasciculus (UF)), while some callosal fibers (CC splenium and parts of the forceps major) only showed significant increase in parts of the tracts
For Mean diffusivity (MD), bilateral decrease was found for cingulum-hippocampus gyrus (CHG), UF and forceps minor, while decrease in the left hemisphere and no change or increase was found in the right hemisphere for some White matter (WM) tracts (CST, superior longitudinal fasciculus (SLF) and IFOF)
For MD, there was a trend toward an association between change and motion tp1 (F = 3.52, p ≤ .062) where less decrease in MD was associated with more motion, and motion at tp2 (F = 2.92, p ≤ .090) where more decrease in MD was associated with more motion, and for axial diffusivity (AD), there was an effect of motion at tp1 (F = 11.51, p ≤ .001) where less decrease in AD was associated with more motion, and motion at tp2 (F = 10.72, p ≤ .001) where more decrease in AD was associated with more motion
Summary
How the microstructural connectivity changes in the preschool and early school years proceed along major WM tracts, and how they can be described along major spatial gradients in the brain, i.e. posterior-to-anterior, medial-to-lateral and inferior-tosuperior, have not been thoroughly characterized longitudinally. This will be addressed in the present study. A few longitudinal studies are confirming widespread WM FA increases, and mean (MD) and radial (RD) diffusivity decreases through late childhood and adolescence, but the results for axial diffusivity (AD) are less consistent (Bava et al, 2010, Giorgio et al, 2010, Lebel and Beaulieu, 2011, Brouwer et al, 2012). Development of diffusion directionality and magnitude in WM, possibly related to an underlying increase in the diameter and myelination of axons, among other factors, may play a role in cognitive development during childhood and adolescence (Johansen-Berg, 2010, Vestergaard et al, 2011, Peters et al, 2014)
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