| The microstructural integrity of the white matter of the brain declines with age, as does regional brain volume and cognition, all in a differential manner. One potential mechanism of these declines is vascular impairment. The goal of the current study was to characterize these white matter age-differences across several regions of interest (ROIs), relate these age-differences to regional gray and white matter volume, and to gauge the effect of regional white matter integrity on various domains of cognition in a healthy lifespan sample. Vascular risk was also examined for its effect on white matter integrity. Fifty-two healthy adults (19-81 years old) underwent MRI scans of the head (structural and diffusion tensor imaging), completed neuropsychological testing, and had blood pressure measured. Manual tracing of ROIs was conducted to measure volumes and anisotropy and diffusivity of white matter tracts. Results indicated lesser integrity of the white matter with age in the prefrontal, parietal, occipital white matter ROIs, as well as the genu and splenium of the corpus callosum and portions of the internal capsule, with the prefrontal and occipital regions being most affected. Most regions displayed an accelerated trajectory of diffusivity with age and prefrontal white matter anisotropy exhibited a linear decline until age 50, when decline began to decelerate. Decrements in regional white matter integrity predicted both gray and white matter volumes in adjacent and distal regions both intra- and inter-hemispherically. Regional white matter integrity differentially evidenced significant effects on processing speed (prefrontal, genu, parietal), various executive function components (working memory: frontal, genu, internal capsule; Stroop: parietal, occipital; task switching: genu, frontal, parietal, occipital), and fluid (but not crystallized) intelligence (parietal, occipital, internal capsule). Hypertension, despite being treated and controlled, exerted a strong negative influence on white matter anisotropy and diffusivity beyond the effects of age, and both systolic and diastolic blood pressure showed a strong dose-response relation to regional anisotropy and diffusivity, strongest in the posterior portions of the brain. This study suggests that both healthy aging and hypertension exert sufficient negative influence on regional white matter integrity to impose a neural disconnection that is manifested in age-related cognitive decline. |
