Abstract
Language representation in the bilingual brain is the result of many factors, of which age of appropriation (AoA) and proficiency of the second language (L2) are probably the most studied. Many studies indeed compare early and late bilinguals, although it is not yet clear what the role of the so-called critical period in L2 appropriation is. In this study, we carried out coordinate-based meta-analyses to address this issue and to inspect the role of proficiency in addition to that of AoA. After the preliminary inspection of the early (also very early) and late bilinguals’ language networks, we explored the specific activations associated with each language and compared them within and between the groups. Results confirmed that the L2 language brain representation was wider than that associated with L1. This was observed regardless of AoA, although differences were more relevant in the late bilinguals’ group. In particular, L2 entailed a greater enrollment of the brain areas devoted to the executive functions, and this was also observed in proficient bilinguals. The early bilinguals displayed many activation clusters as well, which also included the areas involved in cognitive control. Interestingly, these regions activated even in L1 of both early and late bilingual groups, although less consistently. Overall, these findings suggest that bilinguals in general are constantly subjected to cognitive effort to monitor and regulate the language use, although early AoA and high proficiency are likely to reduce this.
Highlights
How does the brain of a bilingual person work? Research on this topic has extensively developed in the last decades, with an increasing number of studies devoted to the identification of the brain areas activated when bilinguals perform language tasks in the known languages
The final sample consisted of 57 papers (53 fMRI and four PET studies), from which we identified the groups of early bilinguals (74 experiments; 536 foci; 1,048 subjects), very early bilinguals (17 experiments; 91 foci; 227 subjects), and late bilinguals (174 experiments; 1,351 foci; 2,519 subjects), see Supplementary Table S1 for paper list details
We reported the coordinates in the Montreal Neurological Institute (MNI) standard space
Summary
How does the brain of a bilingual person work? Research on this topic has extensively developed in the last decades, with an increasing number of studies devoted to the identification of the brain areas activated when bilinguals perform language tasks in the known languages. Given the definition of a bilingual as a person that masters more than one language or dialect (see Fabbro, 1999, 2001), Bilinguals’ Language Brain Networks it appears clear that this may apply to a wide range of individuals. For this reason, the bilinguals assessed in the published studies rarely form consistent and homogeneous groups. Some authors set it around puberty, a period during which language skills fully develop (e.g., Lenneberg, 1967; Long, 1990; Locke and Bogin, 2006), whereas others suggest the period around 6–7 years of age to be crucial, because, after this age, learning some linguistic skills becomes challenging (e.g., Johnson and Newport, 1989)
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