Effective Connectivity of Aphasic Bilingual Semantic Processing
Robert Buckshaw II1, Erin Meier1, Swathi Kiran1; 1Boston University
In a world becoming increasingly bilingual, it is essential to understand how bilingual individuals process meaning. Bilingual adults with aphasia (BAA) who have semantic deficits secondary to stroke can experience impairments that leave them unable to communicate in either language. As such, the current study aimed to characterize connectivity between two key regions implicated in semantic control: inferior frontal gyrus, pars triangularis (IFGtri) and posterior middle temporal gyrus (pMTG), during a semantic association task in four BAA and four age-matched, healthy bilingual controls (BHC). We used fMRI and dynamic causal modeling (DCM) and created a model space to test hypotheses regarding the nature of semantic processing in term of directionality (i.e., feedforward [MTG-IFG] vs. feedback [IFG-MTG]) and laterality (i.e., left, right, or bilateral lateralization). The best fit model for the majority of participants was represented by a bilateral feedback connectivity model. However, as some participants favored other models, parameter analysis was done using data from single subject best fit models. The results showed that BHC have stronger intrinsic connections (i.e., in the absence of task) than BAA. By contrast, BAA have stronger task-driven connections than BHC. These results suggest that patients experience more functional disconnect between IFGtri and pMTG than controls at rest but must rely on the connectivity between these regions to a greater extent during a task requiring semantic control. Ultimately, knowing how left hemisphere damage impacts semantic network connectivity will allow for better therapeutic treatment for those suffering from aphasia.
Topic Area: LANGUAGE: Semantic