Imagine the brain as a communication network, with cortical regions sending messages to each other through white matter fibers. Just like a telephone wire can degrade over time, the age-related degeneration of white matter in the brain can affect communication between these regions. In this study, researchers investigated how the blood oxygenation level dependent (BOLD) signals in white matter are affected by the natural aging process. By analyzing these signals, they found that the intensities of BOLD signals and the connections between functional units in white matter were significantly impacted by aging. Furthermore, graph-theoretical analysis revealed a decrease in the ability of remote white matter regions to exchange information with each other as a result of aging. These findings indicate that imaging markers derived from white matter BOLD signals can provide valuable insights into the effects of aging on brain function. Curious to learn more about how our brains change as we get older? Check out the full research article!

IntroductionThe aging brain is characterized by decreases in not only neuronal density but also reductions in myelinated white matter (WM) fibers that provide the essential foundation for communication between cortical regions. Age-related degeneration of WM has been previously characterized by histopathology as well as T2 FLAIR and diffusion MRI. Recent studies have consistently shown that BOLD (blood oxygenation level dependent) effects in WM are robustly detectable, are modulated by neural activities, and thus represent a complementary window into the functional organization of the brain. However, there have been no previous systematic studies of whether or how WM BOLD signals vary with normal aging. We therefore performed a comprehensive quantification of WM BOLD signals across scales to evaluate their potential as indicators of functional changes that arise with aging.MethodsBy using spatial independent component analysis (ICA) of BOLD signals acquired in a resting state, WM voxels were grouped into spatially distinct functional units. The functional connectivities (FCs) within and among those units were measured and their relationships with aging were assessed. On a larger spatial scale, a graph was reconstructed based on the pair-wise connectivities among units, modeling the WM as a complex network and producing a set of graph-theoretical metrics.ResultsThe spectral powers that reflect the intensities of BOLD signals were found to be significantly affected by aging across more than half of the WM units. The functional connectivities (FCs) within and among those units were found to decrease significantly with aging. We observed a widespread reduction of graph-theoretical metrics, suggesting a decrease in the ability to exchange information between remote WM regions with aging.DiscussionOur findings converge to support the notion that WM BOLD signals in specific regions, and their interactions with other regions, have the potential to serve as imaging markers of aging.

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