Comparative analysis of cerebellar lobule structure in early, late bilinguals, and monolinguals: A cerebellum lobule-segmentation study

The structural changes in the cerebellum of early bilinguals (EBs) and late bilinguals (LBs) remain unclear, as learning a second language influences the brain. To explore how early bilingualism impacts cerebellar structure, we analyzed gray matter (GM) volume and cerebellar cortical thickness in individuals with EB, LB, and monolinguals (MLs). The T1-weighted images of 28 EB (English Spanish), 30 LB (English-Spanish), and 32 ML (English) participants were obtained from OpenNEURO (https://openneuro.org) and segmented using volBrain CERES 1.0 (https://volbrain.net/services/CERES) to compare cerebellar GM volume and cortical thickness. We performed cerebellum lobule-wise segmentation analysis on groups matched for age, education, and gender. We found that, compared to the ML group, the LB group showed a larger GM volume in the right lobule III, and compared to the EB group, the LB group had greater cortical thickness in the left lobule IX. No other significant differences were found among the groups. Although there was a positive correlation between the age of second language acquisition and lobule IX cortical thickness in participants from the EB and LB groups no other significant differences were observed among the groups. In summary, by examining the structural differences in cerebellar GM volume and cortical thickness among EBs, LBs, and MLs, we found that later second-language acquisition is linked to increased GM volume in right lobule III and greater cortical thickness in left lobule IX. These findings suggest experience-dependent cerebellar plasticity related to the age at which second language acquisition occurs.