Table 1.

Key findings of non-DTI magnetic resonance imaging studies of typical white matter microstructural development from 0–25 years since 2007 are summarized. Studies using a variety of imaging techniques find rapid maturation in early childhood (~0–5 years) suggesting ongoing myelination. Studies in older children and adolescents find increases of NDI, but no changes or slight decreases in MTR. Studies using only DTI have been omitted from this table as they are numerous, and have been listed elsewhere in recent reviews (Dubois et al., 2014; Lebel et al., 2017; Qiu et al., 2015; Tamnes et al., 2017).

Paper	N	Ages (years)	Modality (analysis)	Model Used	Key Findings of White Matter Microstructural Changes with Age

Perrin 2008 (Perrin et al., 2008)	408	12–18	T1, MTR (ROI – only CST)	Linear	MTR decrease with age in male adolescents; suggests no major myelin changes in adolescence

Leppert et al, 2009 (Leppert et al., 2009)	114	0–4.5	T2 relaxometry (ROIs)	Exponential	Rapid, nonlinear decreases of T2 across early childhood in corpus callosum, caudate and thalamus; evidence of posterior-to-anterior progression

Paydar 2014 (Paydar et al., 2014)	59	0–4.6	DKI, DTI (ROIs)	Exponential	Increases of FA, MK in all ROIs except FA in putamen; largest increases of FA & MK in frontal & parietal WM, ALIC

Dean 2015 (Dean et al., 2015)	108	0.2–5.5 (longitudinal	MWF (ROIs)	Gompertz	Gompertz function – slow, fast, slow
Dean 2015 (Dean et al., 2015)	108	0.2–5.5 (longitudinal	MWF (ROIs)	Gompertz	Sex differences, associations with cognitive abilites

Jelescu 2015 (Jelescu et al., 2015)	55	0–2.75	WMTI, NODDI (ROIs)	Linear, exponential	Increases of intra-axonal water and tortuosity, trend increase in WMTI but not NODDI fiber alignment in splenium and genu; smaller increases in PLIC

Dean 2016 (Dean et al., 2016)	18	0.25–7.5	g-ratio (from mcDESPOT & NODDI)	Logarithmic	Decreases throughout brain, continuing across age range

Moura 2016 (Moura et al., 2016)	176	7–14	MTR (ROIs) and DTI (TBSS, also above in table)	Age bin comparisons	No MTR-DTI correlation; no age-related changes in MTR
Moura 2016 (Moura et al., 2016)	176	7–14	MTR (ROIs) and DTI (TBSS, also above in table)	Age bin comparisons	Widespread FA increases and MD and RD decreases, and small clusters where AD decreases

Pangelinan 2016 (Pangelinan et al., 2016)	941/761	12–19	MTR, T1	Linear	Decreasing MTR, T1 intensity in male adolescents, but not in females; changes in males are mediated by puberty stage and bioavailable testosterone

Zhang 2016 (Zhang et al., 2016)	82	0.2–15.5	MT and APT	Exponential	APTW decreasing exponential, MTR increasing exponential

Genc 2017 (Genc et al., 2017a)	72	4–19	NODDI ROIs	Linear, quadratic, cubic	Widespread increases of NDI; NDI more strongly related to age than any other parameter

Mah 2017 (Mah et al., 2017)	27	8–13	NODDI	Linear	Widespread increases of NDI; no change in ODI
Mah 2017 (Mah et al., 2017)	27	8–13	Probabilistic tractography	Linear	Widespread increases of NDI; no change in ODI

MTR: magnetization transfer ratio; DKI: diffusion kurtosis imaging; MWF: myelin water fraction; APT: amide proton transfer; NODDI: neurite orientation dispersion and density imaging; NDI: neurite density index; ODI: orientation dispersion index; ROI: region of interest, TBSS: tract based spatial statistics, FA: fractional anisotropy, MD: mean diffusivity, AD: axial diffusivity, RD: radial diffusivity; ILF/SLF: inferior/superior longitudinal fasciculus; UF: uncinate fasciculus; CST: corticospinal tracts