Mapping the principal gradient on the corpus callosum. A) Visualisation of the principal gradient on the cortical surface. B) Examples for percentage maps (20-40-60%) depicting associated cortical areas. C) Percentage-specific tractograms as derived from the percentage gradients maps shown in B. D) Midsagittal display of callosal connectivity based on the tractograms for the 20th, 40th and 60th gradient percentages. Callosal areas with low probabilities (red) indicate that fewer participants showed connections to the particular gradient percentage in this area. The prevalence across gradient values for 12 exemplary voxels is depicted in supplementary figure S1-A. E) Callosal gradient map (left), which was computed as the weighted average of callosal connectivity across all percentage maps of the gradient with the 7 Wittelson regions parcellation superimposed. The distribution of gradient values along the Wittelson parcellation scheme is shown on the right. For a hard-border classification of voxels to gradient values please see supplementary figure S1-B. F) Scatterplots showing the relation between callosal connectivity (left) or number of non-zero connectivity voxels (right) and the residual between the gradient corrected for the number of voxels in the respective gradient percentage map. By callosal connectivity, we mean interindividual probability of connection.