Review Article DOI 10.3349/ymj.2011.52.4.553 pISSN: 0513-5796, eISSN: 1976-2437 Yonsei Med J 52(4):553-557, 2011 Somatotopic Arrangement and Location of the Corticospinal Tract in the Brainstem of the Human Brain Sung Ho Jang Department of Physical Medicine and Rehabilitation, College of Medicine, Yeungnam University, Daegu, Korea. Received: March 14, 2011 Corresponding author: Dr. Sung Ho Jang, Department of Physical Medicine and Rehabilitation, College of Medicine, Yeungnam University, 317-1 Daemyeong 5-dong, Nam-gu, Daegu 705-717, Korea. Tel: 82-53-620-3269, Fax: 82-53-620-3269 E-mail: strokerehab@hanmail.net ∙ The author has no financial conflicts of interest. © Copyright: Yonsei University College of Medicine 2011 This is an Open Access article distributed under the terms of the Creative Commons Attribution Non- Commercial License (http://creativecommons.org/ licenses/by-nc/3.0) which permits unrestricted non- commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. 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 ar- rangement 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). There- fore, 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. Key Words: Corticospinal tract, somatotopy, brainstem, cerebral peduncle, mid- brain, pons, medulla INTRODUCTION The corticospinal tract (CST) is the major neuronal pathway for motor function in the human brain.1-4 The CST is known to be critical in recovery of motor weakness following brain injury, particularly with regard to fine motor activity of the hands.2,4-7 Many previous studies have reported that the CST has somatotopy along the pathway of the human brain.8-21 Detailed knowledge of CST somatotopy would be helpful in establishing scientific rehabilitative strategies, estimating reha- bilitative period, establishing guidelines for invasive procedures, and predicting fi- nal outcomes for patients with brain injury. The CST descends through an area at the brainstem that is narrower than the su- pratentorial area in the human brain.1,22 Therefore, even a small lesion at the brain- stem can cause severe motor weakness. The anatomical location of CST at the brainstem has been well-documented in neuroanatomy textbooks and stud- ies.1,9,10,12,15,22-33 However, little is known about the somatotopic location and ar- rangement of the CST at the brainstem.8,11,16-19,21,34,35 Recent developments in diffu- sion tensor tractography (DTT), which is derived from diffusion tensor imaging Yonsei Med J http://www.eymj.org Volume 52 Number 4 July 2011 553