Age-related changes in brain functional activation have been characterized by both age-related cortical over-and under-recruitment compared to young adults. Evidence from working memory domain has demonstrated that such neural responses reflect age-related differences in modulation of neural activity in response to increasing memory loads. The main focus of this thesis is to show that age-related cortical recruitment is modulated by task demands, constrained by individual’s white matter integrity and external experience. In Experiment 1, I use the functional magnetic resonance imaging (fMRI) to reveal reduced BOLD-measured activity in older compared to young adults under demanding conditions in executive processing task, indicating clearly that the older adults have reduced or limited capacity of recruiting more neural resources in response to increasing task demands during cognitive control. In Experiment 2, I use the diffusion tensor imaging (DTI) to show that individual differences in micro-structural integrity of white matter, particular in corpus callosum, relate to both bilateral cortical recruitment and task performance in young and older adults, suggesting reduced capacity to modulate neural resources in response to changing task demands in older adults may be contributing factor of age-related degradation in white matter integrity of callosar fibers. Finally, in Experiment 3, I additionally show the impact of cultural biases in contrast to fundamental biological effect in aging on bilateral cortical recruitment, suggesting that culture-related neural differences may remain at the same level throughout the lifespan. The series of studies jointly provide the evidence for age-related differences in modulation of cortical recruitment that may stem from structural changes in white matter integrity and culture-related differences in processing style.
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Aging and cortical recruitment in response to cognitive challenge
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