White Matter Asymmetry in the Human Brain: A Diffusion Tensor MRI Study

TLDR

Language ability and handedness are likely linked to asymmetry of the cerebral cortex and white‑matter connectivity, yet previous voxel‑based morphometry studies have shown inconsistent white‑matter differences and failed to detect handedness effects. The study aimed to investigate white‑matter asymmetries in two independent subject groups using diffusion‑tensor imaging. Diffusion‑tensor imaging was employed, and voxel‑based statistical analyses were applied to assess asymmetries in white‑matter composition. Voxel‑based analyses revealed a left‑hemisphere asymmetry of the arcuate fascicle and handedness‑related differences in precentral‑gyrus white matter, findings that were robust in small samples and demonstrate DTI’s sensitivity for detecting white‑matter tissue differences.

Abstract

Language ability and handedness are likely to be associated with asymmetry of the cerebral cortex (grey matter) and connectivity (white matter). Grey matter asymmetry, most likely linked to language has been identified with voxel-based morphometry (VBM) using T(1)-weighted images. Differences in white matter obtained with this technique are less consistent, probably due to the relative insensitivity of the T(1) contrast to the ultrastructure of white matter. Furthermore, previous VBM studies failed to find differences related to handedness in either grey or white matter. We revisited these issues and investigated two independent groups of subjects with diffusion-tensor imaging (DTI) for asymmetries in white matter composition. Using voxel-based statistical analyses an asymmetry of the arcuate fascicle was observed, with higher fractional anisotropy in the left hemisphere. In addition, we show differences related to handedness in the white matter underneath the precentral gyrus contralateral to the dominant hand. Remarkably, these findings were very robust, even when investigating small groups of subjects. This highlights the sensitivity of DTI for white matter tissue differences, making it an ideal tool to study small patient populations.