Early childhood bilingualism: effects on brain structure and function

Bilingualism Is Associated with Significant Structural and Connectivity Alterations in the Thalamus in Adulthood

Language is a sophisticated cognitive skill that relies on the coordinated activity of cerebral cortex. Acquiring a second language creates intricate modifications in brain connectivity. Although considerable studies have evaluated the impact of second language acquisition on brain networks in adulthood, the results regarding the ultimate form of adaptive plasticity remain inconsistent within the adult population. Furthermore, due to the assumption that subcortical regions are not significantly involved in language-related tasks, the thalamus has rarely been analyzed in relation to other language-relevant cortical regions. Given these limitations, we aimed to evaluate the functional connectivity and volume modifications of thalamic subfields using magnetic resonance imaging (MRI) modalities following the acquisition of a second language. Structural MRI and fMRI data from 51 participants were collected from the OpenNeuro database. The participants were divided into three groups: monolingual (ML), early bilingual (EB), and late bilingual (LB). The EB group consisted of individuals proficient in both English and Spanish, with exposure to these languages before the age of 10 years. The LB group consisted of individuals proficient in both English and Spanish, but with exposure to these languages after the age of 14 years. The ML group included participants proficient only in English. Our results revealed that the ML group exhibited increased functional connectivity in all thalamic subfields (anterior, intralaminar-medial, lateral, ventral, and pulvinar) compared with the EB and LB groups. In addition, a significantly decreased volume of the left suprageniculate nucleus was found in the bilingual groups compared with the ML group. This study provides valuable evidence suggesting that acquiring a second language may be protective against dementia, due to its high plasticity potential, which acts synergistically with cognitive functions to slow the degenerative process.

The Differences in the Whole-Brain Functional Network between Cantonese-Mandarin Bilinguals and Mandarin Monolinguals

Cantonese-Mandarin bilinguals are logographic-logographic bilinguals that provide a unique population for bilingual studies. Whole brain functional connectivity analysis makes up for the deficiencies of previous bilingual studies on the seed-based approach and helps give a complete picture of the brain connectivity profiles of logographic-logographic bilinguals. The current study is to explore the effect of the long-term logographic-logographic bilingual experience on the functional connectivity of the whole-brain network. Thirty Cantonese-Mandarin bilingual and 30 Mandarin monolingual college students were recruited in the study. Resting state functional magnetic resonance imaging (rs-fMRI) was performed to investigate the whole-brain functional connectivity differences by network-based statistics (NBS), and the differences in network efficiency were investigated by graph theory between the two groups (false discovery rate corrected for multiple comparisons, q = 0.05). Compared with the Mandarin monolingual group, Cantonese-Mandarin bilinguals increased functional connectivity between the bilateral frontoparietal and temporal regions and decreased functional connectivity in the bilateral occipital cortex and between the right sensorimotor region and bilateral prefrontal cortex. No significant differences in network efficiency were found between the two groups. Compared with the Mandarin monolinguals, Cantonese-Mandarin bilinguals had no significant discrepancies in network efficiency. However, the Cantonese-Mandarin bilinguals developed a more strongly connected subnetwork related to language control, inhibition, phonological and semantic processing, and memory retrieval, whereas a weaker connected subnetwork related to visual and phonology processing, and speech production also developed.