INVESTIGATING THE NEURAL CORRELATES OF LANGUAGE SWITCHING IN SPANISH ENGLISH BILINGUALS EMPLOYING EFFECTIVE CONNECTIVITY ANALYSES
Ramos Nunez, Aurora Isabel 1975-
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Bilingualism requires individuals to manage their two languages in order to communicate with others. They may voluntarily or involuntarily switch back and forth between their two languages. While voluntarily switching between two languages may appear effortless, it requires a tremendous amount of cognitive effort. Previous imaging and language impairment research has shown evidence of a cognitive control mechanism needed for switching between two languages that involves areas such as prefrontal cortex, inferior parietal cortex, anterior cingulate cortex and basal ganglia. This mechanism has been identified as being involved in executive function processes (e.g. working memory, conflict monitoring, set switching and language selection). While previous imaging studies have identified brain areas showing increased activation during language switching tasks, they do not discuss how these areas interact with each other in the healthy bilingual brain. The purpose of this study was to investigate whether or not brain regions involved in the cognitive control processes needed in bilingualism exert influence on each other and how different conditions modulate such connections. Twenty healthy right-handed Spanish-English bilinguals (13 women) between the ages of 18 and 32 participated in an fMRI experiment. Participants overtly named objects in three conditions: Spanish only, English only and mixed (alternating between Spanish and English) in a picture-naming task while inside the scanner. Three cognitive control regions (e.g. prefrontal, parietal, and caudate) and an object recognition region (e.g. fusiform gyrus) were chosen to be included in Dynamic Causal Modeling (DCM) analyses. Three models were created to examine differential modulatory effects of the conditions on the interactions between cognitive control and object recognition regions. Bayesian Model Selection using DCM revealed that the English and Spanish conditions modulated the interactions between the cognitive control and object recognition regions more so than the mixed condition. These results indicated that the three conditions had a differential modulatory effect on brain connections, suggesting that the cognitive control network required for naming is more strongly connected during naming solely in English or Spanish than during naming in the language-switching mixed condition. Is possible that these bilinguals are not used to switching back and forth between their two languages. These findings carry implications for both the bilingual literature in general and the bilingual aphasia literature.