Abstract
BackgroundThe neural networks underpinning language control and domain-general executive functions overlap in bilinguals, but existing evidence is mainly correlative. Here, we present the first neurofunctional evidence for a transfer effect between (domain-general) inhibitory control and language control through training. We trained Chinese–English bilinguals for 8 days using a Simon task taxing the inhibitory control system, whilst an active control group was trained with a color judgment task that does not tax the inhibitory control system. All participants performed a language-switching task before and after training. It has been suggested that the activity of the left DLPFC was associated with domain-general top-down cognitive control (Macdonald et al. Science 288: 1835–1838, 2000) and bilingual language control (Wang et al. Neuroimage 35: 862–870, 2007). In addition, the dACC was closely related to the conflict detection (Abutalebi et al. Cereb Cortex 18:1496–1505, 2008). Last, the activity of the left caudate has been linked with lexical selection (Abutalebi et al. Cereb Cortex 18:1496–1505, 2008), especially the selection of the weak language (Abutalebi et al. Cortex 49: 905–911, 2013). Therefore, we focused on these three regions of interest (ROIs) where neural changes associated with transfer were expected to occur.ResultsThe results showed a negative correlation between changes in activation levels in the left dorsolateral prefrontal cortex (DLPFC) and changes in the switch cost magnitude in the language-switching task in the training group but not in the control group, suggesting that the DLPFC plays a critical role in the transfer effect from domain-general executive functions to language control. However, there was no measurable effect in the anterior cingulate cortex or left caudate nucleus, suggesting that the inhibitory control training increased the neural efficiency for language production in bilinguals in terms of attention shifting and conflict resolution, but the training did not affect conflict detection and lexical selection.ConclusionThese findings showed how cognitive training evidence can help establish a causational link between the neural basis of domain-general executive functions and language control in bilinguals.
Highlights
The neural networks underpinning language control and domain-general executive functions overlap in bilinguals, but existing evidence is mainly correlative
In the two control groups, we found no significant correlation between beta value change and switch cost change in any of the three region of interest (ROI) (active control group: dorsolateral prefrontal cortex (DLPFC) (r = 0.307, p = 0.100), dorsal anterior cingulate cortex (dACC) (r = 0.310, p = 0.098), or left caudate nucleus (LCN) (r = 0.253, p = 0.148); passive control group: DLPFC (r = − 0.279, p = 0.117), dACC (r = -0.145, p = 0.270), or LCN (r = 0.335, p = 0.075)
FMRI results showed no significant difference between the training group and the control groups in the pre-test session, suggesting that the language control ability, and its underlying neural mechanisms, were comparable between the three groups prior to training
Summary
The neural networks underpinning language control and domain-general executive functions overlap in bilinguals, but existing evidence is mainly correlative. We focused on these three regions of interest (ROIs) where neural changes associated with transfer were expected to occur Bilingual individuals activate both languages when using one of their two languages (e.g., [19, 20, 34, 38, 76]). Meuter and Allport [62] showed greater switch costs, that is, the difference in reaction time or error rate between switch and non-switch trials, in forward switches (i.e., from L2 to L1) as compared to backward switches (i.e., from L1 to L2) switches This finding is consistent with assumptions of the Inhibitory Control Model [31]: Unbalanced bilinguals have to inhibit the dominant language (L1) to a greater extent as compared to the non-dominant language (L2) when switching between the two languages, and forward switches are more costly than backward switches. The asymmetry in switch cost has been replicated by numerous studies (e.g., [21, 55, 68]) and the switch cost magnitude is widely regarded as an index for language control capacity in bilinguals
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