Beyond Bilingualism: multilingual experience correlates with caudate volume

Abstract

The multilingual brain must implement mechanisms that serve to select the appropriate language as a function of the communicative environment. Engaging these mechanisms on a regular basis appears to have consequences for brain structure and function. Studies have implicated the caudate nuclei as important nodes in polyglot language control processes, and have also shown structural differences in the caudate nuclei in bilingual compared to monolingual populations. However, the majority of published work has focused on the categorical differences between monolingual and bilingual individuals, and little is known about whether these findings extend to multilingual individuals, who have even greater language control demands. In the present paper, we present an analysis of the volume and morphology of the caudate nuclei in 75 multilingual individuals who speak three or more languages. Volumetric analyses revealed a significant relationship between multilingual experience and right caudate volume, as well as a marginally-significant relationship with left caudate volume. Vertexwise analyses revealed a significant enlargement of dorsal and anterior portions of the left caudate nucleus having connectivity to executive brain regions, as a function of multilingual expertise. These results suggest that multilingual expertise might exercise a continuous impact on the brain, and that as additional languages beyond a second are acquired, the additional demands for control result in modifications to brain structures associated with language management processes.