Anatomical variability in the cortical representation of first and second language

FUNCTIONAL magnetic resonance imaging was used to assess inter-subject variability in the cortical representation of language comprehension processes. Moderately fluent French-English bilinguals were scanned while they listened to stories in their first language (L1 = French) or in a second language (L2 = English) acquired at school after the age of seven. In all subjects, listening to L1 always activated a similar set of areas in the left temporal lobe, clustered along the left superior temporal sulcus. Listening to L2, however, activated a highly variable network of left and right temporal and frontal areas, sometimes restricted only to right-hemispheric regions. These results support the hypothesis that first language acquisition relies on a dedicated left-hemispheric cerebral network, while late second language acquisition is not necessarily associated with a reproducible biological substrate. The postulated contribution of the right hemisphere to L2 comprehension is found to hold only on average, individual subjects varying from complete right lateralization to standard left lateralization for L2.