Functional connectivity during morphosyntactic processing: An fMRI study in balanced Turkish-Persian bilinguals

Previous research has documented the impact of bilingualism on the functional connectivity (FC) of brain networks responsible for processing of two languages during a resting-state brain activity. However, the BOLD signal modulation during task-evoked neural activity remains unclear. To address this question we focused on language-related differences of fMRI-based FC of bilingual brains during morphosyntactic processing in L1 and L2 among balanced L1-Turkish-L2-Persian bilinguals who had learnt L2 at age 7. The task required grammaticality judgements to alternating L1-L2 sentences. In our previous study on the present dataset, we had demonstrated changes in BOLD activation in the Pars opercularis (PO), posterior Superior Temporal Gyrus (pSTG), Planum Temporale (PT), and Supplementary Motor Area (SMA), associated with auditory morphosyntactic processing. In the present reanalysis of these data we focused on FC within and between the language network and the control network. Regions of interest were based on the syntax- and control-specific regions activated by the task. Our findings confirm the FC between the syntax-specific regions PO and pSTG within the language network. The FC between these areas in the processing of morphosyntax turned to be quite similar for L1 and L2, reflecting the high competences of our balanced bilinguals in both languages. In the control network, direct FCs were found in two key areas of the PT and SMA (i.e. left PT to right PT and left PT to left SMA), supporting the view that these areas subserve control operations when bilinguals perceive and process spoken language. Remarkably, inter- and intra-hemispheric connectivities in the control network were indistinguishable for L1 and L2. Regarding intra-network results, although increased FCs were observed in L1 for the left PO-PT neurocircuit and in L2 for the pSTG-PT neurocircuit, none of them significantly interacted with grammaticality. Overall, these results suggest that being balanced bilingual with age of acquisition at 7 years appears to be associated with similarities of FC between syntax processing-related and input- and output-related brain networks. Considering that previous resting state studies had not found evidence for the above-mentioned connections in bilinguals, the present results indicate the importance of task-driven reconfigurations on functional connections between brain networks.