Abstract
Normal aging is associated with reduced cerebral structural integrity and altered functional brain activity, yet the association of aging with the relationship between structural and functional brain changes remains unclear. Using combined diffusion tensor imaging (DTI) and functional magnetic resonance imaging (fMRI) modalities, we hypothesized that aging-related changes in white matter integrity (i.e., fractional anisotropy) was associated with the short- or long-range functional connectivity density (FCD) in hub regions. We tested this hypothesis by using a healthy aging cohort comprised of 140 younger adults aged 20–39 years and 109 older adults aged 60–79 years. Compared with the younger group, older adults exhibited widespread reductions in white matter integrity with selective preservation in brain stem tracts and the cingulum connected to the hippocampus and cingulate cortex, whereas FCD mapping in older adults showed a reduced FCD in the visual, somatosensory, and motor functional networks and an increased FCD in the default mode network. The older adults exhibited significantly increased short- or long-range FCD in functional hubs of the precuneus, posterior, and middle cingulate, and thalamus, hippocampus, fusiform, and inferior temporal cortex. Furthermore, DTI-fMRI relationship were predominantly identified in older adults in whom short- and long-range FCD in the left precuneus was negatively correlated to structural integrity of adjacent and nonadjacent white matter tracts, respectively. We also found that long-range FCD in the left precuneus was positively correlated to cognitive function. These results support the compensatory hypothesis of neurocognitive aging theory and reveal the DTI-fMRI relationship associated with normal aging.
Highlights
Aging is associated with remarkable changes in brain structure and function
The results are similar to the voxel-wise analysis presented in Figure 2, except that no hub region was found to have significantly reduced functional connectivity density (FCD) in older adults compared with younger people
Using a combined diffusion tensor imaging (DTI) and resting-state functional magnetic resonance imaging (fMRI) modalities, we investigated the association of aging with white matter integrity and resting-state functional connectivity, and their relationship in functional connectivity hub regions
Summary
Aging is associated with remarkable changes in brain structure and function. Studies have revealed that, compared with younger adults, older people exhibit reduced brain size, and increased ventricular volume (Scahill et al, 2003), loss of neuronal body or synaptic density (Morrison and Hof, 1997), loss of gray matter intensity (Good et al, 2001), or reduced white matter integrity (Pagani et al, 2008). The quality of structural connections, or white matter integrity, has been suggested to influence functional connectivity of gray matter brain regions (Bennett and Rypma, 2013). In this context, combining structural and fMRI techniques is appropriate for examining the relationship between brain structure and functional changes associated with aging. Diffusion tensor imaging (DTI) can be used to quantify white matter structural integrity, such as fractional anisotropy (FA) value, resting-state BOLD fMRI can reveal functional dependency among different brain regions
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