Functional neural architecture of cognitive control mediates the relationship between individual differences in bilingual experience and behaviour

Brain correlates of attentional load processing reflect degree of bilingual engagement: Evidence from EEG

The present study uses electroencephalography (EEG) with an N-back task (0-, 1-, and 2-back) to investigate if and how individual bilingual experiences modulate brain activity and cognitive processes. The N-back is an especially appropriate task given recent proposals situating bilingual effects on neurocognition within the broader attentional control system (Bialystok and Craik, 2022). Beyond its working memory component, the N-Back task builds in complexity incrementally, progressively taxing the attentional system. EEG, behavioral and language/social background data were collected from 60 bilinguals. Two cognitive loads were calculated: low (1-back minus 0-back) and high (2-back minus 0-back). Behavioral performance and brain recruitment were modeled as a function of individual differences in bilingual engagement. We predicted task performance as modulated by bilingual engagement would reflect cognitive demands of increased complexity: slower reaction times and lower accuracy, and increase in theta, decrease in alpha and modulated N2/P3 amplitudes. The data show no modulation of the expected behavioral effects by degree of bilingual engagement. However, individual differences analyses reveal significant correlations between non-societal language use in Social contexts and alpha in the low cognitive load condition and age of acquisition of the L2/2L1 with theta in the high cognitive load. These findings lend some initial support to Bialystok and Craik (2022), showing how certain adaptations at the brain level take place in order to deal with the cognitive demands associated with variations in bilingual language experience and increases in attentional load. Furthermore, the present data highlight how these effects can play out differentially depending on cognitive testing/modalities - that is, effects were found at the TFR level but not behaviorally or in the ERPs, showing how the choice of analysis can be deterministic when investigating bilingual effects.

Degree of multilingual engagement modulates resting state oscillatory activity across the lifespan

Multilingualism has been demonstrated to lead to a more favorable trajectory of neurocognitive aging, yet our understanding of its effect on neurocognition across the lifespan remains limited. We collected resting state EEG recordings from a sample of multilingual individuals across a wide age range. Additionally, we obtained data on participant multilingual language use patterns alongside other known lifestyle enrichment factors. Language experience was operationalized via a modified multilingual diversity (MLD) score. Generalized additive modeling was employed to examine the effects and interactions of age and MLD on resting state oscillatory power and coherence. The data suggest an independent modulatory effect of individualized multilingual engagement on age-related differences in whole brain resting state power across alpha and theta bands, and an interaction between age and MLD on resting state coherence in alpha, theta, and low beta. These results provide evidence of multilingual engagement as an independent correlational factor related to differences in resting state EEG power, consistent with the claim that multilingualism can serve as a protective factor in neurocognitive aging.

Mapping individual aspects of bilingual experience to adaptations in brain structure

Individual differences in using multiple languages are thought to differentially affect brain structure and function. The present study assessed the neuroanatomical predictions of an emerging theory, the Unifying the Bilingual Experience Trajectories framework, which provides the most comprehensive set of predictions of how individual differences in bilingual experiences lead to specific neural and cognitive adaptations. A total of 140 young adults with variable language experiences were scanned using magnetic resonance imaging and completed demographic questionnaires. Brain structure measures implicated in predictions of the Unifying the Bilingual Experience Trajectories model were extracted and regressed against the model's experiential factors. Consistent with the model's predictions, greater intensity and diversity of bilingual language use resulted in changes in gray matter volume in cortical regions involved in executive control (including inferior frontal gyrus, middle temporal gyrus, angular gyrus, and medial frontal gyrus), indicating adaptations toward handling increased executive control demands. Conversely, duration of bilingual engagement resulted in changes within white matter microstructure (bilateral superior longitudinal fasciculus) and increases in subcortical gray matter (left caudate), indicative of adaptations toward increased efficiency of control. Overall, this research enhances our understanding of how bilingual experiences influence brain structure and provides the first direct empirical evidence for the predictions made by the Unifying the Bilingual Experience Trajectories framework.

Bilingual Spatial Cognition: Spatial Cue Use in Bilinguals and Monolinguals

Structural plasticity changes and functional differences in executive control tasks have been reported in bilinguals compared to monolinguals, supporting a proposed bilingual 'advantage' in executive control functions (e.g., task switching) due to continual usage of control mechanisms that inhibit one of the coexisting languages. However, it remains unknown whether these differences are also apparent in the spatial domain. The present fMRI study explores the use of spatial cues in 15 bilinguals and 14 monolinguals while navigating in an open-field virtual environment. In each trial, participants had to navigate towards a target object that was visible during encoding but hidden in retrieval. An extensive network was activated in bilinguals compared to monolinguals in the encoding and retrieval phase. During encoding, bilinguals activated the right temporal and left parietal regions (object trials) and left inferior frontal, precentral, and lingual regions more than monolinguals. During retrieval, the same contrasts activated the left caudate nucleus and the right dorsolateral prefrontal cortex (DLPFC), the left parahippocampal gyrus, as well as caudate regions. These results suggest that bilinguals may recruit neural networks known to subserve not only executive control processes but also spatial strategies.