Abstract
Aging is associated with microstructural white matter (WM) changes. WM microstructural characteristics, measured with diffusion tensor imaging (DTI), are different in normal appearing white matter (NAWM) and WM hyperintensities (WMH). It is largely unknown how the microstructural properties of WMH are associated with cognition and if there are regional effects for specific cognitive domains. We therefore examined within 200 healthy older participants (a) differences in microstructural characteristics of NAWM and WMH per cerebral lobe; and (b) the association of macrostructural (WMH volume) and microstructural characteristics (within NAWM and WMH separately) of each lobe with measures of executive function and processing speed. Multi-modal imaging (i.e., T1, DTI, and FLAIR) was used to assess WM properties. The Stroop and the Trail Making Test were used to measure inhibition, task-switching (both components of executive function), and processing speed. We observed that age was associated with deterioration of white matter microstructure of the NAWM, most notably in the frontal lobe. Older participants had larger WMH volumes and lowest fractional anisotropy values within WMH were found in the frontal lobe. Task-switching was associated with cerebral NAWM volume and NAWM volume of all lobes. Processing speed was associated with total NAWM volume, and microstructural properties of parietal NAWM, the parietal WMH, and the temporal NAWM. Task-switching was related to microstructural properties of WMH of the frontal lobe and WMH volume of the parietal lobe. Our results confirm that executive functioning and processing speed are uniquely associated with macro- and microstructural properties of NAWM and WMH. We further demonstrate for the first time that these relationships differ by lobar region. This warrants the consideration of these distinct WM indices when investigating cognitive function.
Highlights
Aging is associated with macro- and microstructural white matter (WM) changes (Gunning-Dixon et al, 2009; Bai et al, 2011)
Comparing diffusion values in normal appearing white matter (NAWM) to diffusion values in WM hyperintensities (WMH) for each lobe we found that fractional anisotropy (FA) values within NAWM were significantly higher than FA values within WMH in the frontal and parietal lobe [Cerebrum: t(196) = 26.11, p < 0.001; Frontal: t(195) = 47.60, p < 0.001; Parietal: t(193) = 5.96, p < 0.001; Temporal: t(186) = −1.47, p = 0.143; Occipital: t(194) = −21.41, p < 0.001] and mean diffusivity (MD) values were lower across the cerebrum and within single lobes [Cerebrum: t(196) = 26.11; Frontal: t(195) = −44.56; Parietal: t(191) = −38.95; Temporal: t(186) = −38.31; Occipital: t(194) = −33.18]
Both are associated with overall NAWM volume, but only processing speed is related to microstructural properties of NAWM and WMH of the parietal lobe and NAWM microstructural properties of the temporal lobe
Summary
Aging is associated with macro- and microstructural white matter (WM) changes (Gunning-Dixon et al, 2009; Bai et al, 2011). Teasing apart the association between microstructure of WMH and cognition and microstructure of NAWM and cognition could improve our understanding of brain structural-behavioral relationships. It could provide additional insight in the unique contribution of microstructural alterations next to the well-described macrostructural influences (e.g., WMH and NAWM volume) on cognition. The few studies that have reported diffusion metrics separately for NAWM and WMH found lower FA values and higher diffusion values within WMH (Vernooij et al, 2009; Maniega et al, 2015), and reported that, on a whole brain level, associations between cognitive abilities and microstructural integrity are different within NAWM and WMH (Vernooij et al, 2009; Schmidt et al, 2010; Jokinen et al, 2013)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
