Anatomical location of the frontopontine fibers in the internal capsule in the human brain: a diffusion tensor tractography study.

The frontopontine fibers (FPFs) originate from the frontal lobe and end in the pontine nuclei. Many neuroanatomy textbooks have described the FPFs as descending through the anterior limb of the internal capsule. However, several studies have reported controversial results. In this study, using diffusion tensor tractography, we investigated the anatomical location of the FPFs in the internal capsule in the human brain. We recruited 53 healthy volunteers for this study. For reconstruction of the FPFs, the seed region of interest was given in the medial cerebral peduncle of the reconstructed corticospinal tract. The target regions of interest were placed in the three cerebral cortices, respectively: Brodmann's area (BA) BA 6, BA 8, and BA 9. The anatomical locations of the FPFs were evaluated using the highest probabilistic location in the internal capsule. We measured the relative distance of the FPFs from the middle point at the genu of the internal capsule to the most posterior point of the lenticular nucleus. The relative mean distances of the highest probabilistic location for the FPFs from BA 9, 8, and 6 were 18.18, 32.08, and 43.83% from the middle point of the genu of the internal capsule, respectively. By contrast, the highest probabilistic location for the corticospinal tract was 74.18%. According to our findings, the FPFs were located at the anterior half of the posterior limb in the internal capsule, in the following order, from the anterior direction: the FPFs from BA 9, BA 8, and BA 6.