e Role of the Ventral Fiber Pathway in Language Production in Health and Disease

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While neuroimaging research on language production has traditionally focused primarily on gray ma er, several recent studies highlight the involvement of ventral and dorsal white ma er pathways. e exact functional role of these pathways is a debated issue. e ventral pathway has been suggested to underlie top-down control in language production, but the functional roles of each speci c white ma er tract within this pathway, like the inferior fronto-occipital fasciculus (IFOF) , the inferior longitudinal fasciculus (ILF), and the uncinate fasciculus (UF), have not yet been elucidated. To investigate the involvement of these tracts in top-down control, 16 patients with primary progressive aphasia (PPA), an acquired language de cit due to neurodegenerative disease, and 22 age-matched healthy controls performed a picture-word interference task. is task included an incongruent (semantically related word, e.g., word cow on the picture of a horse) and a neutral (e.g., XXX on the picture of a horse) condition. e stimuli were made of 12 high frequency words from two semantic categories (animals and fruits). e di erence in reaction time and accuracy between semantically related and neutral picture-word pairs, the interference e ect, served as a behavioral measure of the participants’ top-down interference control. Furthermore, the microstructural integrity of the IFOF, the ILF, and the UF was calculated as a neuroanatomical measure with di usion tensor MRI and tractography, based on Fractional Anisotropy (FA) and Mean Di usivity (MD) values. A linear mixed-e ects model revealed that patients were more susceptible to the interference e ect in reaction time compared to controls. Moreover, the integrity of all three tracts was altered in patients compared to controls. Importantly, the integrity of the IFOF was not associated with the interference e ect in reaction times or accuracy. e integrity of the ILF was associated with the interference e ect in reaction times, but not accuracy. e integrity of the UF was associated with the interference e ect in both reaction times and accuracy. ese results indicate that patients with PPA manifest impaired top-down control processes in language production and that these processes are mediated by the microstructural properties of the inferior longitudinal fasciculus and uncinate fasciculus in both patients with PPA and healthy individuals.
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