Human corticospinal tract lateralization at the height of the internal capsule is not related to handedness.

Evaluating the integrity of the corticospinal tract at the height of the posterior limb of the internal capsule with a lateralization index has been applied to predict upper limb motor recovery after stroke in numerous diffusion tensor imaging studies. When comparing patient groups with healthy controls in this context, matching for age and gender is generally recommended. Since a generalized lateralization of diffusion strength to the dominant left hemisphere has been reported, it can be argued that handedness should also be accounted for. To address this question, we used the Human Connectome Project data set containing 1,065 diffusion-weighted MRI sets as well as information on handedness as defined by the Edinburgh Handedness Inventory. We hypothesized that handedness might be related to diffusion strength of the corticospinal tract. As commonly employed, we extracted fractional anisotropy values at the level of the internal capsule to calculate a laterality index. Contrary to our hypothesis, we found no association between corticospinal tract diffusion strength and handedness. We conclude that for handedness, no balancing between patient and control groups is needed when comparing corticospinal tract diffusivity parameters.