Objective To primarily discuss the brain structural underpinnings of learning second language of ethnic minorities and the effects of acquired learning on brain microstructure by analyzing the differences of gray matter density between Bai-Han bilinguals and Han non-bilinguals.

Methods A retrospective analysis was performed on brain MRI data collected from 33 healthy Bai adults who were proficient in Bai and Chinese language (hereafter Bai-Han bilinguals, 18 males and 15 females, aged 20–50 (25.33±4.65) years) and 30 healthy Han adults who were proficient in Chinese language only (hereafter Han non-bilinguals, 13 males and 17 females, aged 20–50 (26.16±2.05) years) in the First Affiliated Hospital of Kunming Medical University from April 2012 to April 2013. Bai-Han bilinguals and Han non-bilinguals underwent MRI scanning to collect three-dimensional T1 structural images, which were used to analyze the grey matter density via voxel-based morphometry. Then, the between-group differences of grey matter density were compared through two-sample t test.

Results Compared with Han non-bilinguals, Bai-Han bilinguals had significantly higher grey matter density in the right middle frontal gyrus (t=4.00, P<0.001), right orbital gyrus (t=2.68, P<0.001), right straight gyrus (t=2.25, P<0.001), left straight gyrus (t=2.69, P<0.001), and left lenticular nucleus (t=3.90, P<0.001).

Conclusion The brain areas with differences in gray matter density between Bai-Han bilinguals and Han non-bilinguals were concentrated in prefrontal cortex and striatum, which were closely correlated with the learning of second language in Bai-Han bilinguals, and acquired learning for second language may give rise to cerebral microstructural alterations.