Onset age of second language acquisition and fractional anisotropy variation in multilingual young adults

Abstract

The experience of speaking two languages, particularly the age of second language acquisition (L2AoA), has been robustly associated with differences in metrics indicative of white matter structure. However, bilingual language experience is complex, described not only by acquisition but also functional language usage and proficiency. We examined whether the onset age of the second most proficient language (pL2AoA) would indeed be a sensitive measure that incorporates onset age of second language acquisition and self-reported L2 proficiency and correlates with variation in fractional anisotropy in white matter. Thirty-one multilingual young adults with a range of L2AoA and pL2AoA from an English-dominant community participated. After accounting for age, gender, nonverbal IQ, and parental education, both L2AoA and pL2AoA were significantly correlated with fractional anisotropy in the corpus callosum. Furthermore, we show that a larger and more extensive cluster in the corpus callosum was correlated with pL2AoA as compared to the conventional L2AoA. • Multilingualism has been associated with structural brain differences. • We correlated onset age of second language acquisition and white matter structures. • Negative correlations were found between onset age of second language and fractional anisotropy (FA) in corpus callosum. • Similar negative correlations were observed between FA in a larger and more extensive cluster in corpus callosum and the onset age of the second most proficient language.