Functional and structural differences in brain networks involved in language processing and control in highly proficient early and late bilinguals
Résumé
Age of acquisition and proficiency have been identified as possible determinants in the neural localization of second language representation and in the nature of control mechanisms. However, the relationship is not yet clear between age of acquisition and proficiency on the one hand, and language switching and executive functions on the other. In the present study, we used anatomical and functional Magnetic Resonance (MR) Imaging to investigate the impact of age of acquisition. Two groups of highly proficient early and late bilinguals, carefully matched in other measures of proficiency, performed an overt picture-naming task in blocked and switched conditions. We found that switching between languages in highly proficient bilinguals involves an increase of activity in areas reported as components associated with domain-general inhibitory processes. There was no effect of task language, only of whether the task involved language switching. Comparing the two groups indicated that highly proficient bilinguals use the same neural network for language production and control regardless of age of acquisition. Structural differences were apparent between the two groups in regions associated with language control. We propose that language switching recruits a neural network that is engaged for domaingeneral executive control functions and that proficiency rather than age of acquisition exerts influence on language representations.
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