White matter disconnection is related to age-related phonological deficits
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ORIGINAL RESEARCH
White matter disconnection is related to age-related phonological deficits Sara B. W. Troutman 1 & Michele T. Diaz 1
# The Author(s) 2019
Abstract Older adults have more language production difficulties than younger adults but display largely comparable language comprehension abilities. The Transmission Deficit Hypothesis suggests that production difficulties stem from an age-related increase in phonological signal transmission failures, while the semantic system, being more redundant than the phonological system, allows comprehension to be relatively preserved despite signal failures. Though the neural instantiation of the Transmission Deficit Hypothesis remains an open question, white matter represents one important factor to investigate. Metrics indicative of white matter connectivity across the brain, namely, Radial Diffusivity (RD) and Fractional Anisotropy (FA) have also been linked to age-related cognitive differences including naming difficulties. Using a Picture-Word Interference (PWI) task with 18 younger and 19 older healthy adults, we found that, across ages, better picture naming in the presence of phonological distractors was associated with lower RD across dorsal (r = −.35, p = .03), ventral (r = −.34, p = .04), and fronto-striatal (r = −.33, p = .04) tracts, and higher FA along dorsal tracts (r = .43, p = .008). The pattern of lower RD and higher FA, which is thought to reflect better white matter structure, points to the dorsal stream tracts as critical for performance on the PWI task. Moreover, the effects of RD and FA on performance were attenuated by the effect of age, reflecting the shared variance between age and white matter as it relates to language production ability. Keywords Diffusion tensor imaging . Phonology . Aging . Picture-word interference . Language production
Introduction Despite relative stability in language comprehension abilities across the lifespan, older adults, typically considered to be individuals over 60 years old, have more language production difficulties compared to younger adults (Burke and Shafto 2008). Cross-sectional work has revealed that older adults experience more tip-of-the-tongue states (Burke et al. 1991), produce more filler-words and pauses in speech (Kemper et al. 1992), and make more naming errors (Feyereisen 1997). Not only do older adults report that language problems are frequent
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s11682-019-00086-8) contains supplementary material, which is available to authorized users. * Michele T. Diaz [email protected] 1
Department of Psychology, Pennsylvania State University, 365 Moore Building, University Park, PA 16802, USA
and frustrating (Ossher et al. 2013), such language difficulties may also elicit negative social interactions (Ryan et al. 1995). As such, explaining the underlying mechanisms of age-related language production deficits has critical downstream consequences for the overall well-being of individuals as they age. Theoretical mod
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