Dynamic Effects of Immersive Bilingualism on Cortical and Subcortical Grey Matter Volumes

Subcortical and cerebellar volume differences in bilingual and monolingual children: An ABCD study

Research suggests that bilingual children experience an extension or delay in the closing of the sensitive/critical period of language development due to multiple language exposure. Moreover, bilingual experience may impact the development of subcortical regions, although these conclusions are drawn from research with adults, as there is a scarcity of research during late childhood and early adolescence. The current study included 1215 bilingual and 5894 monolingual children from the ABCD Study to examine the relationship between subcortical volume and English vocabulary in heritage Spanish bilingual and English monolingual children, as well as volumetric differences between the language groups. We also examined the unique effects of language usage in bilingual children's subcortical volumes. In general, bilingual children had less cerebellar volume and greater volume in the putamen, thalamus, and globus pallidus than monolingual children. English vocabulary was positively related to volume in the cerebellum, thalamus, caudate, putamen, nucleus accumbens, and right pallidum in all children. Moreover, the positive relationship between vocabulary and volume in the nucleus accumbens was stronger for monolingual adolescents than bilingual adolescents. The results are somewhat in line with existing literature on the dynamic volume adaptation of subcortical brain regions due to bilingual development and experience. Future research is needed to further explore these regions longitudinally across development to examine structural changes in bilingual brains.

AoA-L2 and Usage-L2 modulate the functional neuroplasticity of the subcortex

Previous studies revealed structural differences in subcortical regions between monolinguals and bilinguals; however, whether the functional neuroplasticity of the subcortex is modulated by different bilingual experiences remains unclear. Here, we examined the effect of age of second language acquisition (AoA-L2) and usage of L2 (Usage-L2) on subcorto-cortical and intra-subcortical functional connectivity (FC) in bilinguals by using resting-state fMRI data. The relations between brain measurements and bilingual experiences were revealed by using multiple regression analysis. We found that increased AoA-L2 was mainly related to decreased subcortical FC involving the anterior thalamus, basal ganglia, and hippocampus. Increased Usage-L2 at home was mainly associated with decreased subcortical FC of the amygdala, globus pallidus, hippocampus, and nucleus accumbens. The FC of these subcortical regions displayed a positive relation with Usage-L2 in social settings. These findings reveal that bilingual experiences modulate the functional neuroplasticity of the subcortex in different ways.

French Phonological Component Analysis and aphasia recovery: A bilingual perspective on behavioral and structural data

Studies show bilingualism entails an advantage in cognitive control tasks. There is evidence of a bilingual advantage in the context of aphasia, resulting in better cognitive outcomes and recovery in bilingual persons with aphasia compared to monolingual peers. This bilingual advantage also results in structural changes in the right hemisphere gray matter. Very few studies have examined the so-called bilingual advantage by reference to specific anomia therapy efficacy. This study aims to compare the effect of French-Phonological Component Analysis (Fr-PCA) in monolinguals and bilingual persons with aphasia, both at the linguistic and cognitive control level, and to examine the structural impact of left hemisphere lesion location and right hemisphere structural data. Eight participants with chronic aphasia received Fr-PCA for a total of 15 h over 5 weeks. The results showed improved accuracy for treated words and generalization to untreated items and discourse in both groups, and improved Flanker task performance for some participants. Bilingual participants improved more than monolinguals for picture-naming tasks and narrative discourse. Damage to the left postcentral gyrus and the middle frontal gyrus was associated with less therapy-induced improvement. Additionally, left hemisphere damage to the inferior parietal gyrus and postcentral gyrus was associated with reduced cognitive control pre-therapy. Undamaged right hemisphere cortical thicknesses were significantly different between groups; the inferior frontal gyrus and the middle frontal gyrus were greater for the bilingual participants and correlated with cognitive control skills. These results suggest a bilingual advantage in anomia recovery following Fr-PCA, potentially resulting from enhanced cognitive control abilities that could be supported by right hemisphere neural reserve.