Neural correlates of cognitive processing in monolinguals and bilinguals

Abstract

Here we review the neural correlates of cognitive control associated with bilingualism. We demonstrate that lifelong practice managing two languages orchestrates global changes to both the structure and function of the brain. Compared with monolinguals, bilinguals generally show greater gray matter volume, especially in perceptual/motor regions, greater white matter integrity, and greater functional connectivity between gray matter regions. These changes complement electroencephalography findings showing that bilinguals devote neural resources earlier than monolinguals. Parallel functional findings emerge from the functional magnetic resonance imaging literature: bilinguals show reduced frontal activity, suggesting that they do not need to rely on top-down mechanisms to the same extent as monolinguals. This shift for bilinguals to rely more on subcortical/posterior regions, which we term the bilingual anterior-to-posterior and subcortical shift (BAPSS), fits with results from cognitive aging studies and helps to explain why bilinguals experience cognitive decline at later stages of development than monolinguals.

Bilinguals have more complex EEG brain signals in occipital regions than monolinguals

“…Given that greater brain signal complexity is believed to index the ability to rapidly switch brain states (Deco, Jirsa, & McIntosh, 2011; Beharelle Kovačević, McIntosh, & Levine, 2012), these findings suggest a greater ability for bilinguals to switch brain states in occipital (i.e., possibly visual) regions than monolinguals. Recent evidence from our lab suggests that bilinguals are able to disengage attention from visually presented items more rapidly than monolinguals (Grundy et al, 2017, Grundy & Keyvani-Chahi, 2017), a process that requires more advanced visual processing. In these experiments, the items are visually simple like the stimuli used here.…”

“…If bilinguals are more adept at parsing information at an automatic/perceptual level than monolinguals (and hence have greater signal complexity at occipital electrodes), this may help to explain why bilinguals disengage attention more rapidly than monolinguals. This ability is not always expressed as a bilingual advantage to overall behavioral performance because rapidly disengaging is beneficial on trial switches but not trial repetitions (Grundy et al, 2017). …”

“…Cz was chosen because it falls between Pz and Fz. Fourth, based on previous work, there is a general shift from reliance on frontal to reliance on posterior brain region recruitment during non-linguistic processing for bilinguals than monolinguals (Grant, Dennis, & Li, 2014; Grundy, Anderson, Bialystok, 2017). For these reasons in conjunction with the abundance of research using midline sites as representative of processing from anterior to posterior, we chose Fz, Cz, Pz, and Oz.…”

Effects of bilingualism on white matter integrity in older adults

“…The spatial convergence of these beneficial effects is less clear, though a notable exception is the anterior corpus callosum (see Grundy et al, 2017 for a recent review). One possible reason for the spatial inconsistency is the variety of methods that have been used to analyze white matter across studies.…”

“…Speaking two languages on a regular basis has been shown to lead to domain-general cognitive changes that persist across the lifespan (for recent reviews, see Bialystok, 2017; Grundy et al, 2017). However, it is unclear what neural mechanism might underlie these behavioral changes and whether this mechanism persists into old age.…”