IMAGES OF THE MULTILINGUAL BRAIN: THE EFFECT OF AGE OF SECOND LANGUAGE ACQUISITION

Is it the age of second language acquisition (AoA) that primarily determines the manner of cerebral representation of multiple languages in the brain, or is it proficiency? Here, we review recent neuroimaging studies that aimed at investigating AoA effects by comparing early with late (usually with L2 acquisition onset after 6 years of age) bilinguals during a variety of language tasks on a number of languages. Most studies did indeed report AoA effects. Of particular interest is that the region mainly found to functionally differ between early and late bilinguals is the left inferior frontal gyrus, which was modulated during syntactic processing, word generation, and sentence generation. Additionally, differences were observed in gray-matter density of the posterior parietal cortex as well as in right-hemisphere involvement. Interestingly, despite some convergence of findings from a localizational point of view, underlying causes of organizational and functional differences for the effect of AoA on bilingual language processing still remain to be uncovered. Hypotheses currently used for explaining activation differences are described (notably cortical efficiency, executive control, neuroanatomical changes, and right-hemisphere involvement) in relation to AoA and language proficiency.