Cortical maturation and myelination in healthy toddlers and young children

Sean C.L Deoni,Douglas C Dean,Justin Remer,Holly Dirks,Jonathan O’Muircheartaigh

doi:10.1016/j.neuroimage.2015.04.058

Abstract

The maturation of cortical structures, and the establishment of their connectivity, are critical neurodevelopmental processes that support and enable cognitive and behavioral functioning. Measures of cortical development, including thickness, curvature, and gyrification have been extensively studied in older children, adolescents, and adults, revealing regional associations with cognitive performance, and alterations with disease or pathology. In addition to these gross morphometric measures, increased attention has recently focused on quantifying more specific indices of cortical structure, in particular intracortical myelination, and their relationship to cognitive skills, including IQ, executive functioning, and language performance. Here we analyze the progression of cortical myelination across early childhood, from 1 to 6years of age, in vivo for the first time. Using two quantitative imaging techniques, namely T1 relaxation time and myelin water fraction (MWF) imaging, we characterize myelination throughout the cortex, examine developmental trends, and investigate hemispheric and gender-based differences. We present a pattern of cortical myelination that broadly mirrors established histological timelines, with somatosensory, motor and visual cortices myelinating by 1year of age; and frontal and temporal cortices exhibiting more protracted myelination. Developmental trajectories, defined by logarithmic functions (increasing for MWF, decreasing for T1), were characterized for each of 68 cortical regions. Comparisons of trajectories between hemispheres and gender revealed no significant differences. Results illustrate the ability to quantitatively map cortical myelination throughout early neurodevelopment, and may provide an important new tool for investigating typical and atypical development.

Highlights

Cortical maturation is an important feature of neurodevelopment, characterized by both morphometric and microstructural changes
As the T1 relaxation time is related to lipid myelin and macromolecule content, we examined the relationship between T1 and myelin water fraction (MWF) in each cortical region
As myelin constitutes a significant portion of brain volume (Zabin, 1956), it is likely that the increase of cortical myelin is a primary driver of cortical gray matter volume growth

Summary

Introduction

Cortical maturation is an important feature of neurodevelopment, characterized by both morphometric and microstructural changes. While alterations in cortical morphological quantities, including volume, thickness, surface area, and curvature, have been associated with neuropsychiatric, neurological, and developmental disorders (for example, Ecker et al, 2009, 2014; Li et al, 2014; Pacheco et al, 2014; Sierra et al, 2014), differences in the rate of development of these quantities across childhood have been associated with cognitive ability and intelligence (Shaw et al, 2006, 2008). Beyond these gross morphological measures, interest has focused on exploring the underlying cortical cyto- and myeloarchitecture. Changes in the T1w/T2w ratio have been demonstrated across the lifespan (Grydeland et al, 2013; Shafee et al, 2014) from childhood to late adulthood, as well as being associated with cognitive performance (Grydeland et al, 2013)

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Discussion

Conclusion