Somatotopic Arrangement and Location of the Corticospinal Tract in the Brainstem of the Human Brain

The corticospinal tract (CST) is the most important motor pathway in the human brain. Detailed knowledge of CST somatotopy is important in terms of rehabilitative management and invasive procedures for patients with brain injuries. In this study, I conducted a review of nine previous studies of the somatotopical location and arrangement at the brainstem in the human brain. The results of this review indicated that the hand and leg somatotopies of the CST are arranged medio-laterally in the mid to lateral portion of the cerebral peduncle, ventromedial-dorsolaterally in the pontine basis, and medio-laterally in the medullary pyramid. However, few diffusion tensor imaging (DTI) studies have been conducted on this topic, and only nine have been reported: midbrain (2 studies), pons (4 studies), and medulla (1 study). Therefore, further DTI studies should be conducted in order to expand the literature on this topic. In particular, research on midbrain and medulla should be encouraged.

Evaluation of the Somatotopic Organization of Corticospinal Tracts in the Internal Capsule and Cerebral Peduncle: Results of Diffusion-Tensor MR Tractography

OBJECTIVE: We have used diffusion tensor tractography (DTT) for the evaluation of the somatotopic organization of corticospinal tracts (CSTs) in the posterior limb of the internal capsule (PLIC) and cerebral peduncle (CP). MATERIALS AND METHODS: We imaged the brains of nine healthy right-handed subjects. We used a spin-echo echo-planar imaging (EPI) sequence with 12 diffusion-sensitized directions. DTT was calculated with an angular threshold of 35 degrees and a fractional anistropy (FA) threshold of 0.25. We determined the location of the CSTs by using two regions of interest (ROI) at expected areas of the pons and expected areas of the lateral half of the PLIC, in the left hemisphere of the brain. Fiber tracts crossing these two ROIs and the precentral gyrus (PCG) were defined as CSTs. Four new ROIs were then defined for the PCG, from the medial to lateral direction, as ROI 1 (medial) to ROI 4 (lateral). Finally, we defined each fiber tract of the CSTs between the pons and each ROI in the PCG by using two ROIs methods. RESULTS: In all subjects, the CSTs were organized along the long axis of the PLIC, and the hand fibers were located anterior to the foot fibers. The CSTs showed transverse orientation in the CP, and the hand fibers were located usually medial to the foot fibers. CONCLUSION: Corticospinal tracts are organized along the long axis of the PLIC and the horizontal direction of the CP.