Effect of AoA-L2 on L1 and L2 networks in early and late bilinguals

Aim: The age of acquisition of second language (AoA-L2) affects the neural representation of the first language (L1) and L2. Although previous task-fMRI studies showed different activation patterns of language networks in early and late bilinguals, little is known about the effect of AoA-L2 on L1 and L2 resting-state fMRI (rs-fMRI) networks in bilinguals. In this study, we attempted to reveal the differences in resting-state functional connectivity (RSFC) and topological properties of L1 and L2 networks related to AoA-L2 in bilinguals. Design: We pooled 10 early bilinguals and 11 late bilinguals with high proficiency level in L2 (PL-L2) and acquired their brain rs-fMRI data. By taking the brain regions obtained from a previous meta-analysis study as the seeds, we constructed L1 and L2 networks, and then estimated the RSFC and topological properties of L1 and L2 networks. Findings: Significantly higher RSFC between the inferior frontal gyrus (IFG) and lateral occipital gyrus (LOG) in the L1 network, and significantly higher RSFC between the IFG and angular gyrus (ANG) in the L2 network were observed in early bilinguals than in late bilinguals. Early bilinguals showed significantly higher clustering coefficient, global and local efficiency, but lower characteristic path length, than late bilinguals in the L2 network. Originality: Through analyzing the RSFC and topological properties of L1 and L2 networks, we observed the influence of AoA-L2 on the brain neuroplasticity in bilinguals. The findings may provide a new perspective for understanding the neuroplasticity in bilinguals with different L2 experience. Implications: The AoA-L2 affects the RSFC and topological properties of the L2 network more obviously relative to the L1 network in bilinguals. The effect of the L2 experience on the L1 network is hardly detected in bilinguals with high PL-L2.