Imaging structural and functional brain development in early childhood

Abstract

In humans, the period from term birth to ∼2 years of age is characterized by rapid and dynamic brain development and plays an important role in cognitive development and risk of disorders such as autism and schizophrenia. Recent imaging studies have begun to delineate the growth trajectories of brain structure and function in the first years after birth and their relationship to cognition and risk of neuropsychiatric disorders. This Review discusses the development of grey and white matter and structural and functional networks, as well as genetic and environmental influences on early-childhood brain development. We also discuss initial evidence regarding the usefulness of early imaging biomarkers for predicting cognitive outcomes and risk of neuropsychiatric disorders.

Figure 1. Structural brain development in early childhood

a | T1-weighted and T2-weighted images, birth to age 2 years. Note doubling of overall brain size between birth and 1 year with more gradual growth after age 1. In the neonate T1 scan, note that most white matter is not myelinated and therefore appears darker than cortical grey matter. Myelination proceeds rapidly in the first year of life; at 1 year and older, white matter assumes the typical white appearance seen in adults. This rapid change in tissue contrasts presents challenges for image analysis. Also note the relatively thin cortical grey-matter rim in the neonate T1 scan; by age 1, grey-matter thickness has increased significantly, reaching near-maximal thickness. White matter is more intense than grey matter at birth; this pattern is reversed by age 1 year. b | Regional expansion of cortical surface area from birth to 2 years derived from surface reconstructions of T2 (birth) and T1 (ages 1 and 2 years) scans, with greatest expansion in parietal, prefrontal and temporal regions. c | Myelin maturation in the first year of life imaged with mcDESPOT (see Box 2). Myelination begins in central white matter and spreads peripherally. Part a is adapted from REF. . Part b is adapted from REF. . Part c is adapted from REF..

Figure 2. Estimated trajectories of brain structural parameters during development

Relative growth trajectories (depicting percentage change from 20 weeks or neonate scan) in imaging studies of cortical grey and white matter, cortical thickness, surface area and fractional anisotropy (FA) from the prenatal or neonatal period to adulthood. After substantial prenatal development, there is robust postnatal growth of cortical grey-matter volumes in the first 2 years of life, and comparatively slower growth of cortical white-matter volume. FA, a measure of white-matter microstructure, also increases rapidly in the first year of life and much more gradually thereafter, consistent with trajectories of myelination. Cortical thickness peaks at 1–2 years of life and decreases gradually thereafter, whereas surface area develops rapidly in the first year of life and continues to expand thereafter, indicating that cortical volume growth observed after 1–2 years may be driven mainly by surface area expansion. Grey-matter volume and cortical thickness tend to decrease somewhat during adolescence (10–20 years), whereas white-matter volume and FA continue to increase through this period. Figure adapted from REF. .

Figure 3. The development of resting-state functional networks during infancy

This grid of fMRI images depicts the growth of nine resting-state networks (RSNs) during the first year of life, with 3-month intervals between different time points, and in adulthood. Arrows at the top indicate the suggested developmental sequence of different RSNs based on the growth rates of relative degrees of similarity of their spatial topology with corresponding adult ones and the strength of within-network functional connectivity (for more details, see refs ^, ). Colour bar represents Pearson correlation strength between the BOLD signals of each brain voxel with the corresponding seed (green dots denoted in corresponding adult maps in the bottom row). The images are shown in radiological convention (that is, left side of brain on right side of image). All RSNs, including the two lateralized FPN networks (FPN L/R) were defined after Smith et al. SM, sensorimotor network; AUD, auditory network; V1, visual 1 (medial visual) network; V2, visual 2 (occipital pole) network; V3, visual 3 (lateral visual) network; DMN, default-mode network; SA, salience network; FPN, frontoparietal executive control network. Figure adapted from REF. .