Purpose: Brain imaging has provided puzzle pieces in the understanding of language. In neurologically healthy populations, structure of certain brain regions is associated with particular language functions (e.g., semantics, phonology). In studies on focal brain damage, certain brain regions or connections are considered sufficient or necessary for a given language function. However, few of these account for the effects of lesioned tissue on the functional dynamics of the brain for language processing. Here, functional connectivity amongst semantic-phonologic regions of interest (ROIs) is assessed to fill a gap in our understanding about the neural substrates of impaired language and whether connectivity strength can predict language performance on a clinical tool in individuals with aphasia.
Method: Clinical assessment of language, using the Western Aphasia Battery-Revised (WAB-R), and resting-state fMRI data were obtained for 30 individuals with chronic aphasia secondary to left hemisphere stroke and 18 age-matched healthy controls. Functional connectivity (FC) between bilateral ROIs was contrasted by group and used to predict WAB-R scores.
Results: Network coherence was observed in healthy controls and participants with stroke. The left-right premotor cortex connection was stronger in healthy controls, as reported by New et al. (2015) in the same data set. FC of (1) bilateral connections between temporal regions, in the left hemisphere and bilaterally, predicted lexical semantic processing for Auditory Comprehension and (2) ipsilateral connections between temporal and frontal regions in both hemispheres predicted access to semantic-phonologic representations and processing for verbal production.
Conclusions: Network connectivity of brain regions associated with semantic-phonologic processing is predictive of language performance in post-stroke aphasia. The most predictive connections involved right hemisphere ROIs – particularly those for which structural adaptions are known to associate with recovered word retrieval performance. Predictions may be made, based on these findings, about which connections have potential as targets for neuroplastic functional changes with intervention in aphasia.