Superficial white matter across the lifespan: volume, thickness, change, and relationship with cortical features

Abstract

Superficial white matter (SWM) represents a significantly understudied part of the human brain, despite comprising a large portion of brain volume and making up a majority of cortical structural connections. Using multiple, high-quality, datasets with large sample sizes (N=2421, age range 5-100) in combination with methodological advances in tractography, we quantified features of SWM volume and thickness across the brain and across the lifespan. We address four questions: (1) How does U-fiber volume change with age? (2) What does U-fiber thickness look like across the brain? (3) How does SWM thickness change with age? (4) Are there relationships between SWM thickness and cortical features? Our main findings are that (1) SWM volume shows unique volumetric trajectories with age that are distinct from gray matter and other white matter trajectories; (2) SWM thickness varies across the brain, with patterns robust across individuals and across the population at the region-level and vertex-level; (3) SWM shows nonlinear changes across the lifespan that vary across regions; and (4) SWM thickness is associated with cortical thickness and curvature. For the first time, we show that SWM volume follows a similar trend as overall white matter volume, peaking at a similar time in adolescence, leveling off throughout adulthood, and decreasing with age thereafter. Notably, the relative fraction of total brain volume of SWM continuously increases with age, and consequently takes up a larger proportion of total white matter volume, unlike the other tissue types that decrease with respect to total brain volume. This study represents the first characterization of SWM features across the lifespan and provides the background for characterizing normal aging and insight into the mechanisms associated with SWM development and decline.

White matter tract microstructure, macrostructure, and associated cortical gray matter morphology across the lifespan

“…Here we show that total white matter volume plateaus much before FA, which reverses trends before RD and ICVF. The total white matter volume generally peaks around 18-25 years old, which well-matches the total white matter volume trends [74] which reverse at <25 years old. Yet, cortical surface area peaks before white matter volume.…”

Epileptogenic networks in extra temporal lobe epilepsy

“…Third, although most seizure-free patients had no abnormal connections with the RZ, this does not imply there were no abnormalities within the RZ. It would be useful to investigate local white matter tracts within RZ ( Chen, Wang, Kopetzky, Butz-Ostendorf, & Kaiser, 2021 ; Schilling et al, 2022 ; Shastin et al, 2022 ). Finally, the postulated epileptogenic zone defined as the RZ may not represent the true epileptogenic foci.…”

Surface-based Analyses of Diffusional Kurtosis Imaging in Amyotrophic Lateral Sclerosis: Relationship with Onset Subtypes

“…Whereas commonly applied approaches, including tractbased spatial statistics, 16 region-of-interest (ROI) analysis, and tractometry, 17 focus on the core of the major WM bundles, the subcortical WM is gaining attention in studies of both health and disease. 18,19 Histology of ALS has revealed that the degree of pathology, including astrocytosis and astrocyte reactivity, is greater in the subcortical WM than in the GM of the motor cortex. 20 Delamination and unraveling of myelin sheaths in the subcortical WM have also been reported.…”