White-Matter Development is Different in Bilingual and Monolingual Children: A Longitudinal DTI Study

Abstract

Although numerous people grow up speaking more than one language, the impact of bilingualism on brain developing neuroanatomy is still poorly understood. This study aimed to determine whether the changes in the mean fractional-anisotropy (MFA) of language pathways are different between bilingual and monolingual children. Simultaneous-bilinguals, sequential-bilinguals and monolingual, male and female 10–13 years old children participated in this longitudinal study over a period of two years. We used diffusion tensor tractography to obtain mean fractional-anisotropy values of four language related pathways and one control bundle: 1-left-inferior-occipitofrontal fasciculus/lIFOF, 2-left-arcuate fasciculus/lAF/lSLF, 3-bundle arising from the anterior part of corpus-callosum and projecting to orbital lobe/AC-OL, 4-fibres emerging from anterior-midbody of corpus-callosum (CC) to motor cortices/AMB-PMC, 5- right-inferior-occipitofrontal fasciculus rIFOF as the control pathway unrelated to language. These values and their rate of change were compared between 3 groups. FA-values did not change significantly over two years for lAF/lSLF and AC-OL. Sequential-bilinguals had the highest degree of change in the MFA value of lIFOF, and AMB-PMC did not present significant group differences. The comparison of MFA of lIFOF yielded a significantly higher FA-value in simultaneous bilinguals compared to monolinguals. These findings acknowledge the existing difference of the development of the semantic processing specific pathway between children with different semantic processing procedure. These also support the hypothesis that age of second language acquisition affects the maturation and myelination of some language specific white-matter pathways.

Sequential language learning versus language immersion in bilingualism: Diffusion MRI connectometry reveals microstructural evidence

“…In a maturation point of view, these results confirm a temporal significance for critical changes in bilinguals or those using a merging of both languages (14).…”

“…This 141 ranges from individuals being exposed to both languages since or early after birth, and thus are actively participates in verbal-visual incongruence recognition and also in word recognition (14).…”

Neural correlates of cognitive processing in monolinguals and bilinguals

“…Those who took the L2 course showed significant increases in FA in the corpus callosum over time, whereas controls did not. Similarly, Mohades et al . measured FA values for simultaneous bilinguals (L2 from birth), sequential bilinguals (L2 from age 3), and monolinguals (no L2) over a span of 2 years.…”

Neuroanatomical profiles of bilingual children

“…To our knowledge, only two studies have compared the anatomical microstructure of bilingual and monolingual children. Mohades (Mohades et al., ; Mohades et al., ) investigated 8–11‐year‐olds and found that the white matter tract connecting anterior regions of the frontal lobe with posterior regions of the temporo‐occipital lobe in the left hemisphere (i.e., inferior occipitofrontal fasciculus, IFOF) had a higher fractional anisotropy (FA) value in simultaneous bilinguals relative to sequential bilinguals and monolinguals, suggesting that simultaneous bilingual children have more organized IFOF tracts that assist with faster processing of semantic information. Despite the dearth of studies investigating the neuroanatomy of bilingual children, findings from adult studies can suggest some initial predictions about younger populations.…”