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The Role of White Matter Integrity in Age-Related Language Production Differences
Restricted (Penn State Only)
Winter, Sara B
Master of Science
Date of Defense:
March 13, 2018
Michele Theresa Diaz, Thesis Advisor
Nancy Dennis, Committee Member
Lesley Ross, Committee Member
Despite having equal comprehension ability, older adults have more language production difficulties than younger adults (Diaz, Johnson, Burke, & Madden, 2014). According to the Transmission Deficit Hypothesis, language difficulties stem from signal transmission failures which increase with age. The hypothesis holds that the one-to-one mapping of the phonological system creates vulnerability to transmission failures but the many-to-one mapping of semantic networks provides protection from effects of transmission failure (Burke and MacKay, 1991). Alternatively, the Inhibition Deficit Hypothesis would posit that age-related declines in inhibition increase the task-demands of speaking, leading to poorer performance (Hasher & Zacks, 1988). Since white matter integrity has been shown to mediate age-behavior relationships, a potential mechanism underlying both accounts may be age-related white matter integrity declines (Head et al, 2004; Bennet & Madden, 2014). This study explored the relationship between white matter integrity and age-related language deficits using Diffusion Tensor Imaging (DTI) to test hypotheses generated by the Transmission Deficit Hypothesis and the Inhibition Deficit Hypothesis. Findings supported the Transmission Deficit Hypothesis; white matter integrity declined across the brain but the relationship between white matter integrity and outcomes only manifest in phonological behaviors and phonological-task activation. Importantly, age mediated the relationships between white matter integrity and behavioral and activation outcomes, suggesting that white matter integrity decline is a substrate of age-related language production deficits.
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