A study conducted by Stein et al. (201
measured structural changes in the brain’s prefrontal and temporal cortices along with gray matter density, as a result of second language acquisition. The participants, who had minimal knowledge of the target language, underwent an intensive course that lasted three weeks. The researchers observed an increase in gray matter density, especially in the frontal lobes. These changes were directly attributed to second language acquisition.
Martensson et al. (201
conducted another study targeting adult learners, specifically. The researchers observed significantly large increases in cortical thickness due to second language exposure. Increases in hippocampal volume were also noted. Both these studies concluded that language acquisition increases gray matter density and plasticity in the brain.
A third study, published in the Journal of Brain and Language, compared the white matter structure between monolinguals and Spanish-English bilingual adults living in the United States. The studies revealed that immersive learning of a second language increased neuroplasticity and white matter integrity in adult learners.