Myelination of major white matter tracts continues beyond childhood—combining tractography and myelin water imaging

Abstract

27Axonal myelination is a key white matter maturation process as it increases conduction velocity, 28 synchrony, and reliability. While diffusion tensor imaging (DTI) is sensitive to myelination, it is also 29 sensitive to unrelated microstructural properties, thus hindering straightforward interpretations. Myelin 30 water imaging (MWI) provides a more reliable and direct in vivo measure of myelination. Although 31 early histological studies show protracted myelination from childhood to adulthood, reliable tract-32 specific in vivo evidence from MWI is still lacking. Here, we combine MWI and DTI tractography to 33 investigate myelination in middle childhood, late childhood, and adulthood in 18 major white matter 34 tracts. In the vast majority of major white matter tracts, myelin water fraction continued to increase 35 beyond late childhood. Our study provides first in vivo evidence for protracted myelination beyond late 36 childhood. 37 Keywords 38 development, maturation, child, gradient spin echo (GRASE), diffusion tensor imaging (DTI) 39 40

Age-related differences in white matter: Understanding tensor-based results using fixel-based analysis

“…The visual system, of which the forceps major is a part, develops early in life and has high levels of use and automaticity. A prior study found that myelination of the visual system is protracted beyond childhood and could extend into adulthood, which may partially explain our observed increase in FC and FDC in the forceps major (Meissner, Genç, Mädler, & Weigelt, 2019). Previous studies of aging and white matter have supported the last-in-first-out hypothesis which suggests that tracts most vulnerable to decline in aging mature and are myelinated later in development (Raz, 2000(Raz, , 2001Bender, Völkle, & Raz, 2016).…”

Myelin development in visual scene-network tracts beyond late childhood: A multimethod neuroimaging study

“…the inferior longitudinal fasciculus-showed moderate myelin increases from middle childhood to adulthood. However, this remains speculative until other studies can replicate these findings, as our study's population was equal to the one investigated in Meissner, Genç et al (2019). Given that only one scene-network tract showed significant age group differences, it seems that, in contrast to major long distance tracts, short-distant specifically defined scene-network tracts do not necessarily follow the same myelination pattern.…”

“…Recent findings indicate that myelin in a majority of major white matter tracts increases from childhood into young adulthood (Meissner, Genç et al, 2019). In this study, major tracts that may partly subserve scene-network connecting tracts-i.e.…”

“…We refrained from interhemispheric tracking, as DWI and MWI parameters from these tracts would be masked by a major share of general corpus callosum development adding little-if any-insight into scene-network specific development (for corpus callosum development, see Meissner, Genç et al, 2019).…”

“…A series of MWI studies using mcDESPOT investigated infants and young children and found steep increases of myelin from birth to age two and a moderate increase thereafter (Dean et al, 2014;Dean et al, 2015;Deoni et al, 2011;Deoni, Dean, O'Muircheartaigh, Dirks, & Jerskey, 2012;Deoni, Dean, Remer, Dirks, & O'Muircheartaigh, 2015). Recent findings based on mcDESPOT and 3D ME GRASE MWI indicate that while myelin does not seem to increase between middle and late childhood, a pronounced increase of myelin occurs in adolescence in major white matter tracts (Geeraert et al, 2018;Meissner, Genç, Mädler, & Weigelt, 2019). However, scene-network specific data has not been analyzed until now.…”