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Poster D54, Thursday, November 9, 6:15 – 7:30 pm, Harborview and Loch Raven Ballrooms

White Matter Integrity and Language Production in Aging

Sara Winter1, Avery Rizio1, Jack Dempsey1, Kerem Oktar2, Michele Diaz1;1Pennsylvania State University, 2Pomona College

According to the Transmission Deficit Hypothesis, language production difficulties, which are known to increase in aging (Salthouse, 2010), result from signal transmission failures within the language network (McKay & Burke, 1990). One potential mechanism underlying such transmission failures may be declines in white matter integrity, which, according to Head and colleagues (2004), are associated with normal aging. In order to explore the possibility that white matter decline is related to language decline, this study leveraged the dual stream model of language, which implicates dorsal streams in language production and ventral streams in language comprehension (Hickok & Poeppel, 2007). We hypothesized that better dorsal tract integrity, but not ventral tract integrity, would be associated with better performance on a language production task. Further, we predicted that this effect would be larger in older relative to younger adults. To test this hypothesis, 20 younger (18-31) and 20 older (60-79) adults completed a picture word interference task during a functional MRI scan. Participants were asked to name a picture while ignoring either a phonologically-related word, a semantically-related word, an unrelated word, or a non-word. Diffusion MR images were also obtained from participants. Using probabilistic tractography, we modeled two ventral white matter tracts—the Middle Longitudinal Fasiculus and Inferior Longitudinal Fasiculus—and two dorsal white matter tracts—the Superior Longitudinal Fasiculus-III and Frontal Aslant Tract. The average Fractional Anisotropy (FA) along each tract was then calculated for the left hemisphere and squared to meet the assumption of homoscedasticity. Using Pearson’s correlation tests and multiple regression models predicting accuracy from mean FA and age, we analyzed the relationships between FA, age, and accuracy. Dorsal FA was significantly correlated with overall accuracy (r = .40, p < .01) while ventral FA was not significantly correlated with accuracy (r = .15, p = .38). The difference between these correlations was not significant when tested with a Fisher r-to-z transformation (z = 1.18, p = .24). Age was also significantly negatively correlated with accuracy (r = -.56, p < .001) as well as with both ventral (r = -.54, p < .001) and dorsal (r = -.75, p < .001) FA values. In a regression model with age and dorsal FA, dorsal FA was not a significant predictor of accuracy (p = .91) but age was a significant predictor of accuracy (p = .01). Similarly, when predicting accuracy from age and ventral FA, ventral FA was not a significant predictor (p = .17) while age did predict accuracy (p < .001). When including the interaction between age and FA in these models, all predictors were insignificant. These results replicate previous literature showing that white matter integrity and language production ability both decline with age. However, white matter tract integrity did not account for significant variation in language production ability when controlling for age. Further, there was no significant interaction between age and white matter integrity. Together, these results suggest that age may be a proxy variable for a third variable, which influences both white matter integrity and language ability.

Topic Area: Speech Motor Control and Sensorimotor Integration

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