2001 — 2005 |
Reuter-Lorenz, Patricia A. |
R01Activity Code Description: To support a discrete, specified, circumscribed project to be performed by the named investigator(s) in an area representing his or her specific interest and competencies. |
Neurocognitive Aging of Memory and Executive Processes @ University of Michigan At Ann Arbor
Working memory consists of storage mechanisms that hold information on-line for brief intervals and executive processes that can manipulate the stored contents in service of higher cognitive demands. Working memory declines dramatically with age, however the cognitive and neural mechanisms underlying this decline have yet to be identified. We propose a program of research that combines behavioral, functional, and structural neuroimaging analyses to investigate age differences in working memory storage and executive functions. Comparisons of good and poor performers in each age group will be used to distinguish between a continuum of neurocognitive processes, with continuity across the lifespan, versus qualitative changes unique to aging. The working memory circuitry includes several parietal and frontal regions, with left hemisphere prominence for verbal working memory and right hemisphere prominence for spatial working memory. Evidence from positron emission tomography studies indicates that aging (1) alters the laterality of regions recruited by verbal and spatial working memory tasks, and (2) leads to the recruitment of prefrontal sites under conditions that do not necessarily engage these regions in the younger brain. The proposed research has 2 major goals. First, we want to identify the functional significance of the laterality and prefrontal activation differences between younger and older adults. We will use event-related fMRI to identify the cognitive operations associated with these age differences comparing verbal and spatial working memory tasks that emphasize storage. These studies constitute Aim 1 and provide the foundation for investigating executive processes in Aims 2-3. Considerable evidence indicates that executive processes and the frontal regions that mediate them are particularly vulnerable to aging. Therefore, our second major goal is to examine age effects on two executive processes in working memory: (1) the coding of temporal context and (2) the resolution of interference from competing events. For each process our goals are to identify the underlying neural mechanisms, to determine whether the executive mechanisms contribute to encoding, maintenance, and retrieval processes, to determine the extent to which these mechanisms differ for verbal and spatial materials, and to identify whether aging exerts selective effects on these mechanisms that are compensatory in nature or lead to impaired cognitive performance. By obtaining structural measurements of brain regions implicated in working memory, we intend to determine the contribution of age-related atrophy to cognitive performance and to alterations in the neural substrates as revealed through fMRI.
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2014 — 2015 |
Reuter-Lorenz, Patricia A. |
R21Activity Code Description: To encourage the development of new research activities in categorical program areas. (Support generally is restricted in level of support and in time.) |
Working Memory Training, Neural Correlates, and Aging
DESCRIPTION (provided by applicant): Working memory (WM) is a fundamental cognitive ability that declines steadily over the course of normal aging. Mounting evidence suggests however, that with training there is potential for considerable improvement in WM even in older adults (OA). Performance on the WM training tasks can improve markedly and reliably especially when adaptive methods continually adjust task difficulty to changing performance level. While younger adults (YA) typically achieve higher performance than OA and show greater preservation of WM gains over time, OA benefit from WM training, and sustain training benefits even months after training. Critically, the mechanisms underlying such plasticity and the effects of age are largely unknown. Thus, the significant problem addressed by the proposed research is the need to identify the neural markers of working memory plasticity and how they differ due to age. The proposed research uses functional magnetic resonance imaging (fMRI) to investigate the neural bases of improvement on a WM training task in three aims, framed within the Compensation Related Utilization of Neural Circuits Hypothesis (CRUNCH), and other hypothesized mechanisms of plasticity. CRUNCH proposes that the relationship between brain activation and memory load is an inverted-U function regardless of age, as depicted in the specific aims. To compensate for age-related declines, the OA function is shifted left relative to the YA function and consequently OA reach a resource limit at lower loads. This model predicts that training should increase neural efficiency thereby shifting the functions rightward, for both YA and OA, and increasing the range of task demands to which the brain can respond. The CRUNCH framework also makes predictions about how distinctiveness (as measured with multi-voxel pattern analyses, MVPA) and functional connectivity should change due to training. MVPA can provide new evidence about plasticity of domain-specific resources, and connectivity analyses can reveal the plasticity of network circuitry associated WM training. We propose one training experiment (with 20 OA and 20 YA) to conduct a preliminary assessment of (1) univariate, (2) multivariate, and (3) connectivity predictions of CRUNCH in three aims (respectively). The proposed research will test the sensitivity of these measures to WM training in YA and OA in order to demonstrate the feasibility of our approach and establish a strong empirical base to inform power estimates, design and data analysis decisions for a future R01. By identifying the neural correlates of the plasticity underlying training gains, future research cn determine whether such markers can predict the magnitude and maintenance of training gains, the extent and limits of transfer and potentially other cognitive outcomes in YA and OA. The development of interventions that achieve even modest improvements of WM function, especially in the elderly, can potentially maintain effective levels of functioning and stave off further decline.
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