Fig. 2. Improved in vivo human dMRI shows greater agreement with NHP anatomic studies.
Probabilistic tractography from a seed region in the frontal pole is shown for in vivo human dMRI datasets acquired with (a) a higher-resolution protocol (bmax = 10 K s/mm2, 384 directions, 1.5mm resolution), and (b) a lower-resolution protocol (b = 700 s/mm2, 60 directions, 2mm resolution). Based on both anatomic tracing and ex vivo dMRI tractography in NHPs, we expect frontal pole to project through the corpus callosum (CC), internal capsule (IC), and uncinate fasciculus (UF), among other pathways. These projections are present consistently in the higher-resolution human dMRI tractography, while many are missing in the lower-resolution human dMRI tractography. True positives are marked with green arrows; false negatives with yellow arrows. When discrepancies between human dMRI and NHP tracing disappear as dMRI data quality improves, these discrepancies are likely to be dMRI errors and not true inter-species differences.