Abstract

Background: Primary progressive aphasia (PPA) is a clinical dementia syndrome characterized by impairments in language. The presence of Alzheimer disease (AD) neuropathology has been observed in approximately 40% of PPA cases. Cross-sectional and longitudinal features of cortical atrophy in PPA are emerging but less is known about the integrity of subcortical structures, particularly the thalamus. As a major relay station in the brain, the thalamus is implicated in language functioning given its reciprocal connections with perisylvian regions in the cortex. High-dimensional brain mapping was used to characterize thalamic morphology in individuals with and without non-semantic PPA. Further, shape differences were compared between PPA participants with suspected AD pathology (PPAAβ +) and those without suspected AD pathology (PPAAβ -) as determined by amyloid PET scans. The relationship between shape and specific language deficits were also investigated. Method: Thalamic integrity was examined in 57 PPA participants relative to cognitively healthy controls (N=44) with similar demographics. MR scans were acquired using high-resolution T1-weighted MPRAGE volumes following the ADNI protocol. Thalamic shape features were estimated using Large Deformation Diffeomorphic Metric Mapping. Thalamic nuclei of interest included mediodorsal, pulvinar, and anterior regions. General linear models compared differences in thalamic shape between groups. Pearson models characterized relationships between thalamic nuclei and language function. Results: After controlling for whole brain volume, thalamic volume did not differ between groups [F(1, 99)=0.80, p=0.80]. However, PPA participants exhibited significant bilateral inward shape deformation in dorsal and ventral regions that extended in an anterior to posterior fashion, and unilateral outward deformation in medial and lateral regions only in the left thalamus relative to controls [F(9, 91)=5.75, p<0.001, Wilk's Λ=0.64]. There were no shape differences between PPAAβ + and PPAAβ – groups. Pearson models revealed significant correlations between confrontation naming and shape deformation in the left pulvinar (r=0.59, p<0.01) and left anterior (r=0.55, p<0.01) thalamic nuclei for the PPAAβ + group only, such that lower language scores reflected greater localized volume loss. Conclusions: In the absence of volumetric differences, shape measures were able to capture unique aspects of localized morphologic differences in PPA that corresponded to worse naming performance only in those with suspected AD pathology. Thalamic changes appear to be a contributing and unrecognized component to the presentation and language characterization of PPA.

Degree

College and Department

Family, Home, and Social Sciences; Psychology

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