Functional connectivity reveals dissociable ventrolateral prefrontal mechanisms for the control of multilingual word retrieval

A fundamental cognitive operation involved in speech production is word retrieval from the mental lexicon, which in monolinguals is supported by dissociable ventro-lateral prefrontal cortex (vlPFC) mechanisms associated with proactive and reactive control. This functional magnetic resonance imaging (fMRI) study established whether in multilinguals word retrieval is supported by the same prefrontal mechanisms, and whether proactive modulation consists in suppression of the non-target lexicon. Healthy multilingual volunteers participated in a task that required them to name pictures alternatively in their dominant and less-dominant language. Two crucial variables were manipulated: the cue-target interval (CTI) to either engage (long CTI) or prevent proactive control processes (short CTI), and the cognate status of the pictures to-be-named (non-cognates versus cognates) to capture the presence of selective pre-activation of the target language. Results support the two-process account of vlPFC and indicate that multilinguals engage in proactive control to prepare the target language. This proactive modulation, enacted by anterior vlPFC, is achieved by boosting the activation of lexical representations of the target language. Control processes supported by mid-vlPFC and left inferior parietal lobe together, are similarly engaged in pre-and post-word retrieval, possibly exerted on phonological representations to reduce cross-language interference. Significance Statement Word retrieval in monolingual speech production is enacted by left ventro-lateral prefrontal cortex (vlPFC) supporting controlled access to conceptual representations (proactive control), and left mid-vlPFC supporting post-retrieval lexical selection (reactive control). In this functional magnetic resonance imaging (fMRI) study we demonstrate that multilingual word retrieval is supported by similar prefrontal mechanisms. However, differently from monolinguals, multilingual speakers retrieve words by applying proactive control on lexical representations to reduce cross-language interference. Alternatively to what it has been proposed by one of the most influential models, here we show that this proactive modulation is achieved by boosting the activation of lexical representations of the target language.