Structural Asymmetries in the Infant Language and Sensori-Motor Networks

TLDR

Language capacity and hand preference are uniquely human traits linked to hemispheric asymmetries in speech and sensorimotor networks, and early‑life studies are needed to determine whether structural left–right differences drive or result from functional lateralization. The study aimed to identify in vivo structural markers of hemispheric asymmetries in 1–4‑month‑old infants using diffusion tensor imaging. The authors applied three complementary diffusion‑tensor analysis methods focusing on local diffusion indices and tract spatial localization. They found early leftward asymmetries in the arcuate fasciculus and corticospinal tract, indicating that the geometry, micro‑organization, and maturation of these bundles are linked to later functional lateralization.

Abstract

Both language capacity and strongly lateralized hand preference are among the most intriguing particularities of the human species. They are associated in the adult brain with functional and anatomical hemispheric asymmetries in the speech perception–production network and in the sensori-motor system. Only studies in early life can help us to understand how such asymmetries arise during brain development, and to which point structural left–right differences are the source or the consequence of functional lateralization. In this study, we aimed to provide new in vivo structural markers of hemispheric asymmetries in infants from 1 to 4 months of age, with diffusion tensor imaging. We used 3 complementary analysis methods based on local diffusion indices and spatial localizations of tracts. After a prospective approach over the whole brain, we demonstrated early leftward asymmetries in the arcuate fasciculus and in the cortico-spinal tract. These results suggest that the early macroscopic geometry, microscopic organization, and maturation of these white matter bundles are related to the development of later functional lateralization.