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Notwithstanding rising interest, a coherent picture of the brain's representation of two languages has not yet been achieved. In the present meta-analysis we analysed a large number of functional neuroimaging studies focusing on language processing in bilinguals. We used activation likelihood estimation (ALE) to enucleate activation areas involved in bilingual processing and control of different types of linguistic knowledge -lexico-semantics, grammar, phonology -in L1 and L2. Results show that surprisingly, compared to L2, lexico-semantic processing in L1 involves a widespread system of cortico-subcortical regions, especially when L2 is acquired later in life. By contrast, L2 processing recruits regions exceeding the L1 semantic network and relating to executive control processes. Only few regions displayed selective activation for grammar and phonology. Analyses of language switching highlight a functional overlap between domain-general and bilingual language control networks. Collectively, our findings point to a shared neural network for L1 and L2 with few differences depending on the linguistic level. The emerging picture identifies under-investigated issues, offering clear directions for future research.

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The use of socially opprobrious words (taboo words) is a cross-cultural phenomenon occurring between individuals from almost all social extractions. The neurocognitive correlates of using taboo words in the native language (L1) as compared to their use in a second (L2) language are largely unknown. We used fMRI to investigate the processing of taboo and non-taboo stimuli in monolinguals (Experiment 1) and highly proficient bilinguals (Experiment 2) engaged in lexical decision tasks. We report that for L1 socio-pragmatic knowledge is automatically conveyed and taboo words are processed with less effort than non-taboo words. For L2 the processing of taboo words is more effortful and engages additional structures (anterior cingulate cortex, insula) involved in social-norm representation and evaluation. Our results contribute to understand the interface between language and social-norm processing indicating that lexical processing is affected by socio-pragmatic knowledge, but only when the speaker has a contextual use of the language.

The anterior cingulate cortex (ACC) is a key structure implicated in the regulation of cognitive control (CC). Previous studies suggest that variability in the ACC sulcal pattern-a neurodevelopmental marker unaffected by maturation or plasticity after birth-is associated with intersubject differences in CC performance. Here, we investigated whether bilingual experience modulates the effects of ACC sulcal variability on CC performance across the lifespan. Using structural MRI, we first established the distribution of the ACC sulcal patterns in a large sample of healthy individuals (N = 270) differing on gender and ethnicity. Second, a participants' subsample (N = 157) was selected to test whether CC performance was differentially affected by ACC sulcation in bilinguals and monolinguals across age. A prevalent leftward asymmetry unaffected by gender or ethnicity was reported. Sulcal variability in the ACC predicted CC performance differently in bilinguals and monolinguals, with a reversed pattern of structure-function relationship: asymmetrical versus symmetrical ACC sulcal patterns were associated with a performance advantage in monolinguals and a performance detriment to bilinguals and vice versa. Altogether, these findings provide novel insights on the dynamic interplay between early neurodevelopment, environmental background and cognitive efficiency across age.