Structural plasticity in the bilingual brain refers to changes in brain structure due to learning a second language. Research shows that proficiency in a second language and the age at which it is acquired affect grey-matter density in the left inferior parietal cortex. Using voxel-based morphometry, scientists found that bilinguals had greater grey-matter density in this region compared to monolinguals. The effect was more pronounced in early bilinguals, who acquired their second language before age 5, than in late bilinguals, who learned it between 10 and 15 years. Grey-matter density in this region correlated with second-language proficiency and was negatively correlated with the age of acquisition. These findings suggest that the human brain undergoes structural changes in response to language learning, supporting the idea that brain structure is influenced by experience. The inferior parietal region associated with second-language acquisition is also involved in verbal-fluency tasks, indicating a possible link between grey-matter reorganization and cognitive functions. The study highlights a general principle of brain organization, where structural changes in one domain (language) may reflect broader structure–function relationships. The results are consistent with evidence that the brain adapts structurally to environmental demands, such as learning in other domains. The study involved bilinguals and monolinguals, with the latter having little or no exposure to a second language. The findings suggest that the structure of the human brain is altered by the experience of acquiring a second language.Structural plasticity in the bilingual brain refers to changes in brain structure due to learning a second language. Research shows that proficiency in a second language and the age at which it is acquired affect grey-matter density in the left inferior parietal cortex. Using voxel-based morphometry, scientists found that bilinguals had greater grey-matter density in this region compared to monolinguals. The effect was more pronounced in early bilinguals, who acquired their second language before age 5, than in late bilinguals, who learned it between 10 and 15 years. Grey-matter density in this region correlated with second-language proficiency and was negatively correlated with the age of acquisition. These findings suggest that the human brain undergoes structural changes in response to language learning, supporting the idea that brain structure is influenced by experience. The inferior parietal region associated with second-language acquisition is also involved in verbal-fluency tasks, indicating a possible link between grey-matter reorganization and cognitive functions. The study highlights a general principle of brain organization, where structural changes in one domain (language) may reflect broader structure–function relationships. The results are consistent with evidence that the brain adapts structurally to environmental demands, such as learning in other domains. The study involved bilinguals and monolinguals, with the latter having little or no exposure to a second language. The findings suggest that the structure of the human brain is altered by the experience of acquiring a second language.