White-matter connectivity and the reorganization of brain networks in aging

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DESCRIPTION (provided by applicant): A number of functional magnetic resonance imaging (fMRI) studies have show that older individuals often show increased activation outside of the cortical networks typically associated with successful task performance in young adults. Many of these studies have shown that high-performing older adults show both a bilateral pattern of brain activity not observed in young adults or in their low-performing counterparts, as well as a general trend to shift processing from posterior sensory regions to anterior association regions. The models of these patterns, the Hemispheric Asymmetry Reduction in Older adults (HAROLD), and the Posterior to Anterior Shift in Aging (PASA) posit that increases in contralateral and anterior recruitment (CR and AR, respectively) act as compensatory mechanisms for the increase in resource demands brought about by the biological degradation associated with normal aging. To further the understanding of changes in the reorganization of brain networks in aging we seek to identify the neural correlates of CR and AR. We will first seek to show that older adults benefit from bilateral more than unilateral processing (bilateral field advantage: BFA) in a split-visual field paradigm (Specific Aim 1). We will use diffusion tensor imaging (DTI) to evaluate both the structural morphology of the connection that mediate BFA (Specific Aim 2), as well as the influence of white matter integrity on functional networks of activation supporting BFA (Specific Aim 3). We therefore propose a series of multimodal experiments that rely on lateralized matching tasks designed to manipulate intra- and intrahemispheric communication demands between contralateral and ipsilateral brain regions. We expect activations associated with successful performance in older adults to observe a more frontal and bilateral pattern relative to young adult subjects, and that greater fiber integrity will mediate increases in cognitive performance, supporting compensatory accounts of aging. The proposed research program offers several novel approaches to the study of age-related reorganization of effective brain networks, and will clarify the role of white-matter connectivity in supporting healthy aging. Furthermore, this project seeks to characterize mechanisms that help to offset the detrimental effects of aging, and suggests cognitive therapies in both healthy and pathological aging populations.