The role of major associative white matter pathways in language processing
Current neuroanatomical models of language processing point to a critical role of white matter tracts in language processing; data on the relation between tracts’ disconnection and the accompanying language deficits are,
however, fragmentary. Previous studies show that disconnection of the arcuate fasciculus (AF) impairs language production, whereas damage to the ventral tracts leads to a more specific deficit in lexical-semantic processing
(Catani, Mesulam, 2008). The current study aims to systematically reveal a relation between tracts damage and deficits at various aspects of language processing. 35 Russian-speaking right-handed patients (age range: 18–60 years) undergoing brain surgery in the left hemisphere took part in the study. Language assessment was performed before and after surgery using the Russian Aphasia Test (RAT; Ivanova et al., 2013), tapping into all linguistic levels of language processing in both production and comprehension modalities. Patients underwent diffusion-tensor imaging before and after surgery; the data were preprocessed in FSL and ExploreDTI, then TracVis was used to reconstruct AF, frontal aslant tract (FAT), inferior fronto-occipital, inferior longitudinal and uncinate fasciculi (the ventral tracts). We observed a significant correlation (p < 0.007) between smaller postoperative volume of the AF and language production worsening (average production score). Among RAT production subtests analyzed separately, however, only repetition scores demonstrated a significant
positive correlation with AF volume. FAT resection was associated with worse discourse production. No correlation between damage to the ventral tracts and comprehension scores was found. The obtained results are in line with the existing data on the role of the white matter tracts in language processing and suggest that the language production impairment following AF disconnection may be driven specifically by a sensory-motor integration deficit. A correlation
between FAT volume and discourse production supports its critical role in spontaneous speech production.
The study was supported by the Russian Foundation for Basic Research, grant No18-012-00829.