Parcellation of motor cortex-associated regions in the human corpus callosum on the basis of Human Connectome Project data.

The corpus callosum (CC) is the largest white matter structure of the brain and offers the structural basis for an intense interaction between both cerebral hemispheres. Especially with respect to the interaction of both motor cortices it shows a differentiated somatotopic organization. Neuropathological processes are often reflected in structural alterations of the CC and a spatially precise description of structures for the healthy brain is essential for further differentiation of structural damage in patients. We performed a fine-grained parcellation of the CC on 1065 diffusion-weighted data sets of the Human Connectome Project. Interhemispheric tractograms between interhemispherically corresponding functional subdivisions of the primary motor cortex (M1; Brainnetome Atlas) were calculated, transformed into a common space, averaged and thresholded, to be assessed for localization, fractional anisotropy (FA) and mean diffusivity (MD). Spatially distinct CC regions for each functional M1 subdivision (lower and upper limbs, head/face, tongue/larynx) were identified and will be available as anatomical masks. Non-parametrical statistics for the average FA and MD values showed significant differences between all callosal regions. The newly proposed callosal regions allow for a precise differentiation of M1-M1 motor connectivity and the structural integrity of these tracts. Availability of masked regions in a common space will help to better understand inter-hemispherical callosal connectivity in patients or healthy volunteers.