Beyond the cortex: Cerebellar contributions to apraxia of speech in stroke survivors.

Apraxia of Speech (AOS) is a motor speech disorder affecting speech planning and coordination, often co-occurring with aphasia after left hemisphere stroke. While commonly linked to cortical damage, the cerebellum's role remains underexplored. This study examined associations between cerebellar gray matter volume and AOS severity in individuals with chronic left hemisphere cortical stroke. Participants from the Aphasia Recovery Cohort (N = 142) completed structural MRI and AOS assessment using the Apraxia of Speech Rating Scale. Regional cerebellar gray matter volumes were extracted from T1-weighted scans using MATLAB, SPM12, CAT12, and the SUIT atlas, adjusted for total intracranial volume. Multiple linear regressions and partial correlations tested relationships between cerebellar volume and AOS severity, controlling for lesion volume, age, and time post-stroke. Reduced volume in right cerebellar regions was significantly associated with greater AOS severity. Right lobule V was the strongest predictor (R2 = .167, β = -.346, p < .001), followed by lobule VI (R2 = .130, β = -.290, p < .001) and vermis VIIb (R2 = .117, β = -.262, p < .001). Right hemisphere volume overall was more predictive (R2 = .116) than the left (R2 = .080). Dysarthria models showed weaker associations, indicating specificity to AOS. These findings demonstrate that cerebellar structural integrity, particularly in the contralateral right hemisphere, contributes to AOS severity models. Results support expanding AOS models beyond cortical regions and suggest cerebellar-targeted strategies may enhance post-stroke speech rehabilitation models.