Microstructural Changes of the Human Brain from Early to Mid-Adulthood.

Lixia Tian,Lin Ma

doi:10.3389/fnhum.2017.00393

Abstract

Despite numerous studies on the microstructural changes of the human brain throughout life, we have indeed little direct knowledge about the changes from early to mid-adulthood. The aim of this study was to investigate the microstructural changes of the human brain from early to mid-adulthood. We performed two sets of analyses based on the diffusion tensor imaging (DTI) data of 111 adults aged 18–55 years. Specifically, we first correlated age with skeletonized fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD) and radial diffusivity (RD) at global and regional level, and then estimated individuals’ ages based on each DTI metric using elastic net, a kind of multivariate pattern analysis (MVPA) method that aims at selecting the model that achieves the best trade-off between goodness of fit and model complexity. We observed statistically significant negative age-vs-FA correlations and relatively less changes of MD. The negative age-vs-FA correlations were associated with negative age-vs-AD and positive age-vs-RD correlations. Regional negative age-vs-FA correlations were observed in the bilateral genu of the corpus callosum (CCg), the corticospinal tract (CST), the fornix and several other tracts, and these negative correlations may indicate the earlier changes of the fibers with aging. In brain age estimation, the chronological-vs-estimated-age correlations based on FA, MD, AD and RD were R = 0.62, 0.44, 0.63 and 0.69 (P = 0.002, 0.008, 0.002 and 0.002 based on 500 permutations), respectively, and these results indicate that even the microstructural changes from early to mid-adulthood alone are sufficiently specific to decode individuals’ ages. Overall, the current results not only demonstrated statistically significant FA decreases from early to mid-adulthood and clarified the driving factors of the FA decreases (RD increases and AD decreases, in contrast to increases of both measures in late-adulthood), but highlighted the necessity of considering age effects in related studies.

Highlights

With the advent of diffusion tensor imaging (DTI), novel opportunities emerged for in vivo characterization of the brain’s white matter microstructure
These results indicate an overall decrease of fractional anisotropy (FA) and axial diffusivity (AD) and increase of radial diffusivity (RD) from early to mid-adulthood
When we modeled the mean of each DTI metric as a quadratic function of age (A ×2 + C), the fitting parameters indicate inverse U-shaped age-related FA changes and U-shaped age-related mean diffusivity (MD), AD and RD changes (Supplementary Figure S1)

Summary

Introduction

With the advent of diffusion tensor imaging (DTI), novel opportunities emerged for in vivo characterization of the brain’s white matter microstructure. Numerous studies have been performed on the maturation and aging of the human brain using such DTI metrics as fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD) and radial diffusivity (RD; Salat et al, 2005; Madden et al, 2009; Dennis and Thompson, 2013; Kulikova et al, 2015) According to these studies, FA increases and MD decreases with maturation (Qiu et al, 2008; Giorgio et al, 2010; Lebel et al, 2012; Krogsrud et al, 2016), and FA decreases and MD increases with aging in a majority of white matter tracts (Sullivan and Pfefferbaum, 2006; Charlton et al, 2008; Lebel et al, 2012; de Groot et al, 2016). The changes of the human brain from early to mid-adulthood may largely be overwhelmed by those with maturation and aging, as the former may be relatively small as compared to the latter

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