Abstract
Cortical atrophy and degraded axonal health have been shown to coincide during normal aging; however, few studies have examined these measures together. To lend insight into both the regional specificity and the relative timecourse of structural degradation of these tissue compartments across the adult lifespan, we analyzed gray matter (GM) morphometry (cortical thickness, surface area, volume) and estimates of white matter (WM) microstructure (fractional anisotropy, mean diffusivity) using traditional univariate and more robust multivariate techniques to examine age associations in 186 healthy adults aged 20–94 years old. Univariate analysis of each tissue type revealed that negative age associations were largest in frontal GM and WM tissue and weaker in temporal, cingulate, and occipital regions, representative of not only an anterior‐to‐posterior gradient, but also a medial‐to‐lateral gradient. Multivariate partial least squares correlation (PLSC) found the greatest covariance between GM and WM was driven by the relationship between WM metrics in the anterior corpus callosum and projections of the genu, anterior cingulum, and fornix; and with GM thickness in parietal and frontal regions. Surface area was far less susceptible to age effects and displayed less covariance with WM metrics, while regional volume covariance patterns largely mirrored those of cortical thickness. Results support a retrogenesis‐like model of aging, revealing a coupled relationship between frontal and parietal GM and the underlying WM, which evidence the most protracted development and the most vulnerability during healthy aging.
Highlights
The healthy adult brain is susceptible to structural degradation of both grey and white matter tissue throughout the aging process
Few studies have taken this dependency into account by examining the joint contribution of both grey and white matter tissue to investigate how alterations in both aspects of brain structure are related across the lifespan
The current study aims to first utilize univariate analyses of each tissue type in an attempt to replicate and enhance previous lifespan aging work, examining linear and quadratic age associations with grey matter cortical thickness, volume, and surface area, as well as with white matter fractional anisotropy and mean diffusivity; and second to utilize multivariate analyses combining, in turn, measures of grey matter thickness, surface area, and volume, with white matter fractional anisotropy and mean diffusivity to evaluate covariance patterns
Summary
The healthy adult brain is susceptible to structural degradation of both grey and white matter tissue throughout the aging process. Separate partial least squares correlation analyses were applied to examine how estimates of neuronal degradation were associated across the lifespan: two each (one for FA and one for MD) for each of the grey matter regional measures (cortical thickness, surface area, volume) for a total of 6 analyses.
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