Anatomical correlates of sentence comprehension and verbal working memory in neurodegenerative disease

This study investigates whether sentence comprehension and nonsyntactic verbal working memory (vWM) are sustained by the same or by different neural systems. Scores in a sentence-picture matching task and in digits backward (DB) were correlated with magnetic resonance imaging voxelwise gray matter volumes using voxel-based morphometry in 58 patients with neurodegenerative diseases. Results showed that overall sentence comprehension scores, regardless of grammatical structure, correlated with gray matter volumes in the left temporoparietal region, whereas DB scores correlated with dorsolateral prefrontal and inferior parietal volumes. Comprehension of multiclausal relative sentences (type 3) significantly correlated with voxels in the dorsal portion of the left inferior and middle frontal gyri. When DB and multiclausal relative sentences were directly compared, they showed overlapping neural substrates in the dorsolateral left frontal region, supporting a single source of vWM for syntactic and nonsyntactic tasks. Within this large area of common involvement, a small portion of pars triangularis showed an independent effect of multiclausal sentences, whereas a region in the middle frontal gyrus showed greater correlation with DB. This study reconciles two opposing views, which hold that sentence comprehension and vWM rely on either the same or different anatomical resources.