Abstract
Increasing age is associated with deficits in a wide range of cognitive domains as well as with structural brain changes. Recent studies using diffusion tensor imaging (DTI) have shown that microstructural integrity of white matter is associated with cognitive performance in elderly persons, especially on tests that rely on perceptual speed. We used structural equation modeling to investigate associations between white matter microstructure and cognitive functions in a population-based sample of elderly persons (age ≥ 60 years), free of dementia, stroke, and neurological disorders (n = 253). Participants underwent a magnetic resonance imaging scan, from which mean fractional anisotropy (FA) and mean diffusivity (MD) of seven white matter tracts were quantified. Cognitive functioning was analyzed according to performance in five task domains (perceptual speed, episodic memory, semantic memory, letter fluency, and category fluency). After controlling for age, FA and MD were exclusively related to perceptual speed. When further stratifying the sample into two age groups, the associations were reliable in the old-old (≥78 years) only. This relationship between white matter microstructure and perceptual speed remained significant after excluding persons in a preclinical dementia phase. The observed pattern of results suggests that microstructural white matter integrity may be especially important to perceptual speed among very old adults.
Highlights
Diffusion tensor imaging (DTI) is a non-invasive magnetic resonance imaging (MRI) technique that is sensitive to the microstructure of white matter
Better performance in the perceptual speed (PS) domain was related to higher fractional anisotropy (FA) in forceps major (FMAJ) and inferior fronto-occipital fasciculus (IFOF) and lower mean diffusivity (MD) in cingulum that extends to the hippocampus (CHC), corticospinal tract (CS), FMAJ, and IFOF
In exploring this association further, the link was reliable among the very old (≥78 years), but not in the 60-72 years-old subsample. These observations were made in a sample free from dementia and other neurological disorders, and remained after excluding persons in a preclinical dementia phase
Summary
Diffusion tensor imaging (DTI) is a non-invasive magnetic resonance imaging (MRI) technique that is sensitive to the microstructure of white matter. DTI measures the diffusion of water molecules in brain tissue and enables visualization of white matter pathways and quantification of aspects of microstructure, with measures such as fractional anisotropy (FA) and mean diffusivity (MD). Higher FA is associated with greater directionality of water molecules and implies higher fiber density or coherence in a voxel. Normal aging is associated with deficits in many cognitive domains, with the largest age-related differences usually observed for perceptual speed [2,3]. Several studies have examined associations between indices of white matter microstructure and cognitive performance. Lower FA and higher MD in normal-appearing white matter in elderly persons has most consistently been associated with worse performance on tests tapping perceptual speed and executive functioning [4,5,6]
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