Language lateralization shifts with learning by adults.

For the majority of the population, language is a left-hemisphere lateralized function. During childhood, a pattern of increasing left lateralization for language has been described in brain imaging studies, suggesting that this trait develops. This development could reflect change due to brain maturation or change due to skill acquisition, given that children acquire and refine language skills as they mature. We test the possibility that skill acquisition, independent of age-associated maturation can result in shifts in language lateralization in classic language cortex. We imaged adults exposed to an unfamiliar language during three successive fMRI scans. Participants were then asked to identify specific words embedded in Norwegian sentences. Exposure to these sentences, relative to complex tones, resulted in consistent activation in the left and right superior temporal gyrus. Activation in this region became increasingly left-lateralized with repeated exposure to the unfamiliar language. These results demonstrate that shifts in lateralization can be produced in the short term within a learning context, independent of maturation.