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Dorsolateral vs Ventrolateral Precentral Gyrus Atrophy in Primary Progressive Aphasia Linked to Distinct Networks and Motor Speech Patterns
Poster Session A, Friday, September 12, 11:00 am - 12:30 pm, Field House
Maria Luisa Mandelli1, Zoe Ezzes1, Chiara Gallingani1,2, Lisa Wauters1,3, Willa Keegan-Rodewald1, Rian Bogley1, Diana Rodriguez1, Jet MJ Vonk1, Zachary Miller1, Maria Luisa Gorno-Tempini1, Gregory Hickok4; 1Memory and Aging Center, Department of Neurology, University of California San Francisco, San Francisco, CA, 2Department of Biomedical, Metabolic and Neural Sciences, University of Modena and Reggio Emilia, Modena, Italy, 3Department of Speech, Language and Hearing Sciences, University of Texas Austin, USA, 4Department of Cognitive Sciences, University of California Irvine, Irvine, CA, USA
Background: The precentral gyrus has been implicated in motor speech disorders including apraxia of speech (AOS). Recently, it has been proposed that the lateral precentral gyrus contains two parallel systems, dorsal precentral speech area (dPCSA) involved in prosodic coordination and ventral precentral speech area (vPCSA) involved in phonetic coordination, paralleling the prosodic and phonetic subtypes of AOS. In this study, leveraging a cohort of individuals with primary progressive aphasia (PPA), we aimed to test two hypotheses: (i) the dPCSA and vPCSA are part of distinguishable neural circuits, as revealed by different patterns of associated atrophy, and (ii) differential disruption to the two PCSAs is associated with distinct clinical presentations. Methods: T1-weighted MRI from 104 individuals with non-fluent PPA were processed with SPM12 to obtain voxel-wise grey and white matter W-scores indexing deviation from an age-matched control cohort. Mean W-scores were extracted from two 5 mm spheres centered on vPCSA (x=–56, y=8, z=20) and dPCSA (x=–50, y=–4, z=46). Subjects with significantly greater atrophy (W < –1.65) in one region than the other were designated vPCSA-predominant (n=16) or dPCSA-predominant (n=9). Group-level frequency maps summarized atrophy patterns. Auditory–perceptual ratings of specific features of apraxia of speech (AOS), dysarthria, and dysphonia were conducted by three trained speech–language pathologists, and group differences were evaluated using chi‑squared tests. Results: The groups did not differ in age or general disease severity. The vPCSA group exhibited extensive bilateral grey‑ and white‑matter loss encompassing left inferior frontal, inferior parietal and supplementary motor cortices; perisylvian white matter; thalamus; insula; hippocampus; and middle cingulum. Conversely, the dPCSA group showed focal bilateral atrophy along the precentral gyrus with left‑lateralized involvement of supplementary motor area, superior and middle temporal gyri, insula and thalamus. No brainstem or midbrain atrophy was detected. Speech evaluation was not performed on four subjects due to severe motor impairment. AOS was present in both groups (11 out of 13 subjects tested in the ventral group, 7/8 in the dorsal) with largely overlapping feature profiles. Chi-squared tests showed that initiation impairment was significantly more prevalent in the vPCSA group (χ² = 7.14, p = 0.008). Dysarthria was more frequent in vPCSA‑predominant patients (11/13 vs 3/8; χ² = 4.95, p = 0.026), whereas a trend toward harsher vocal quality characterized the dPCSA group (χ² = 3.34, p = 0.067). Dysphonia occurred more frequently in vPCSA (11/13, 84.6% vs 4/7, 57.1%), without reaching significance. Discussion: Both vPCSA and dPCSA non-fluent PPA groups presented with motor speech disorders, including AOS. While several speech features were equally distributed in our small sample, some features differed between groups, suggesting that the two areas contribute differently to motor speech deficits. Additionally, the underlying neural circuits–demonstrated by patterns of correlated atrophy throughout the brain–differed between groups, consistent with the hypothesis of distinguishable circuits. One notable difference is the implication of the dPCSA in auditory-related regions, consistent with previous results in healthy individuals. Future directions include validating these results in independent cohorts and expanding the imaging and clinical features explored.
Topic Areas: Speech Motor Control, Disorders: Acquired