The Influence of Handedness on White Matter Microstructure: Investigation of Quantitative Anisotropy Based on the Human Connectome Project

In previous white matter (WM) studies, the findings have been inconsistent regarding whether WM microstructure is modulated by handedness. Such inconsistency could be due to the impact of crossing fibres on traditional diffusion metrics like fractional anisotropy (FA), as well as the very fact that handedness is a concept defined by comparing the left and right sides of the body/brain. As such, locally defined diffusion metrics may be insensitive to handedness on its own. As a remedy, we proposed to use quantitative anisotropy (QA), an improved anisotropy metric, to construct QA-based laterality indices (LI-QA). Diffusion data from young adult righthanders (n=128) and non-right-handers (n=128) matched in both sex and age were obtained from the Human Connectome Project, to be tested for handedness-induced structural differences. As expected, whereas QA-based correlational tractography was insensitive to handedness, voxel-based analyses on LI-QA revealed interesting patterns of lateralisation and association with handedness.