The Role of White Matter Integrity in Age-Related Language Production Differences

Restricted (Penn State Only)
Author:
Winter, Sara B
Graduate Program:
Psychology
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
March 13, 2018
Committee Members:
  • Michele Theresa Diaz, Thesis Advisor
  • Nancy Dennis, Committee Member
  • Lesley Ross, Committee Member
Keywords:
  • Aging
  • Language
  • white matter
Abstract:
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.