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

Abstract

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 lessdominant 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-benamed (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 StatementWord 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.All rights reserved. No reuse allowed without permission.(which was not peer-reviewed) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity.

Is there proactive inhibitory control during bilingual and bidialectal language production?

“…So, our results are similar to the behavioral results of Branzi et al (2020), who also did not observe a significant interaction between CSI and cognate status with Spanish-Basque-English multilinguals. If proactive language control relies on inhibition, one would expect to see less crosslanguage activation with a long preparation time, since the long preparation time would allow for more proactive inhibition of the non-target language.…”

“…This model converged and yielded a main effect of CSI Length, with slower responses in the No CSI condition (1131.0 ms) than in the Long CSI condition (1092.6 ms). This pattern is in line with many, but not all (e.g., Branzi et al, 2020), bilingual studies that investigated the effect of CSI in mixed language blocks (e.g., Graham & Lavric, 2021;Stasenko et al, 2017), and could be taken as evidence that increased proactive language control leads to better performance.…”

“…It should be noted that Branzi et al (2020) did observe fMRI evidence for proactive inhibitory control. More specifically, the bilateral anterior ventrolateral prefrontal cortex showed a reduction in the long versus short CSI for the cognate effect.…”

“…An additional manipulation was that half the pictures were cognate words between L1 and L3 and the other half were non-cognates. Cognates are words with a similar form/phonology across two languages and are typically processed faster than noncognates because the representations of both languages are activated leading to facilitation at the phonological level (e.g., Branzi et al, 2020;Christoffels et al, 2007). The logic behind the cue-to-stimulus interval (CSI) manipulation and the cognate status manipulation was that if proactive inhibitory control was implemented during the interval between the cue and the picture, it would reduce the activation of the non-target language, leading to a decrease of the cognate facilitation effect.…”

“…In the current study, we set out to further examine the possibility of proactive inhibitory control by relying on the logic put forward in Branzi et al (2020), with a smaller cognate facilitation effect with a long than short CSI providing evidence for proactive inhibitory control. Unlike Branzi and colleagues, however, we would mainly rely on RT analyses.…”