For a bilingual human, every utterance requires a choice about which language to use. This choice is commonly regarded as part of general executive control, engaging prefrontal and anterior cingulate cortices similarly to many types of effortful task switching. However, although language control within artificial switching paradigms has been heavily studied, the neurobiology of natural switching within socially cued situations has not been characterized. Additionally, although theoretical models address how language control mechanisms adapt to the distinct demands of different interactional contexts, these predictions have not been empirically tested. We used MEG (RRID: NIFINV:nlx_inv_090918) to investigate language switching in multiple contexts ranging from completely artificial to the comprehension of a fully natural bilingual conversation recorded “in the wild.” Our results showed less anterior cingulate and prefrontal cortex involvement for more natural switching. In production, voluntary switching did not engage the prefrontal cortex or elicit behavioral switch costs. In comprehension, while laboratory switches recruited executive control areas, fully natural switching within a conversation only engaged auditory cortices. Multivariate pattern analyses revealed that, in production, interlocutor identity was represented in a sustained fashion throughout the different stages of language planning until speech onset. In comprehension, however, a biphasic pattern was observed: interlocutor identity was first represented at the presentation of the interlocutor and then again at the presentation of the auditory word. In all, our findings underscore the importance of ecologically valid experimental paradigms and offer the first neurophysiological characterization of language control in a range of situations simulating real life to various degrees.SIGNIFICANCE STATEMENT Bilingualism is an inherently social phenomenon, interactional context fully determining language choice. This research addresses the neural mechanisms underlying multilingual individuals' ability to successfully adapt to varying conversational contexts both while speaking and listening. Our results showed that interactional context critically determines language control networks' engagement: switching under external constraints heavily recruited prefrontal control regions, whereas natural, voluntary switching did not. These findings challenge conclusions derived from artificial switching paradigms, which suggested that language switching is intrinsically effortful. Further, our results predict that the so-called bilingual advantage should be limited to individuals who need to control their languages according to external cues and thus would not occur by virtue of an experience in which switching is fully free.

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For multilingual individuals, adaptive goal-directed behavior as enabled by cognitive control includes the management of two or more languages. This work used magnetoencephalography (MEG) to investigate the degree of neural overlap between language control and domain-general cognitive control both in action and perception. Highly proficient Arabic-English bilingual individuals participated in maximally parallel language-switching tasks in production and comprehension as well as in analogous tasks in which, instead of the used language, the semantic category of the comprehended/produced word changed. Our results indicated a clear dissociation of language control mechanisms in production versus comprehension. Language-switching in production recruited dorsolateral prefrontal regions bilaterally and, importantly, these regions were similarly recruited by category-switching. Conversely, effects of language-switching in comprehension were observed in the anterior cingulate cortex and were not shared by category-switching. These results suggest that bilingual individuals rely on adaptive language control strategies and that the neural involvement during language-switching could be extensively influenced by whether the switch is active (e.g., in production) or passive (e.g., in comprehension). In addition, these results support that humans require high-level cognitive control to switch languages in production, but the comprehension of language switches recruits a distinct neural circuitry. The use of MEG enabled us to obtain the first characterization of the spatiotemporal profile of these effects, establishing that switching processes begin ϳ400 ms after stimulus presentation.

Traditional research in bilingualism has consistently found that switching languages is effortful, placing demands on neural systems of cognitive control. This finding runs counter to most bilinguals' intuitive experience. We review a body of recent work showing that, in fact, when bilinguals switch languages voluntarily, both the behavioral cost of switching and the associated recruitment of cognitive control areas are greatly reduced or completely eliminated. This suggests that switching languages is not inherently effortful, but rather, particular communicative demands may make it costly. The new evidence also challenges the basic premise underlying the bilingual advantage hypothesis. We articulate a more nuanced version of it, in which the advantage is limited to bilinguals who frequently switch languages based on external constraints. Language-Switching and Traditional Ways to Model It Commanding more than one language is the norm for the majority of the world's population [1,2], and multilingualism has been notably increasing in recent years [3]. A remarkable feature of multilingual individuals is their ability to quickly and accurately switch back and forth between their different languages. Thus, multilingual individuals not only command each of their languages independently, but they are additionally able to alternate and coordinate the rules that govern each language. What are the mechanisms that allow bilingual individuals to effectively do this? How are these systems organized to achieve seamless transitions from one language to the other? Highlights Results of traditional language switching tasks have suggested that language switching is behaviorally effortful and requires increased involvement of cognitive control areas. Recent evidence has challenged this conclusion, showing that when bilinguals are allowed to switch languages freely, this cognitive effort and behavioral cost are either greatly reduced or completely eliminated.

Research on the mental representation of human language has convincingly shown that sign languages are structured similarly to spoken languages. However, whether the same neurobiology underlies the online construction of complex linguistic structures in sign and speech remains unknown. To investigate this question with maximally controlled stimuli, we studied the production of minimal two-word phrases in sign and speech. Signers and speakers viewed the same pictures during magnetoencephalography recording and named them with semantically identical expressions. For both signers and speakers, phrase building engaged left anterior temporal and ventromedial cortices with similar timing, despite different linguistic articulators. Thus the neurobiological similarity of sign and speech goes beyond gross measures such as lateralization: the same fronto-temporal network achieves the planning of structured linguistic expressions.