STRUCTURE OF THE HUMAN SENSORIMOTOR SYSTEM .1. MORPHOLOGY AND CYTOARCHITECTURE OF THE CENTRAL SULCUS

We have studied the morphology of the central sulcus and the cytoarchi tecture of the primary sensorimotor cortex in 20 human brains obtained at autopsy. Although the surface appearance of the central sulcus var ies greatly from brain to brain (and between hemispheres of individual brains), its deep structure is remarkably consistent. The fundus of t he central sulcus is divided into medial and lateral limbs by a comple x junction midway between the sagittal and Sylvian fissures. Based on functional imaging studies, this junction appears to be a structural h allmark of the sensorimotor representation of the distal upper extremi ty. We also identified and measured area 4 (primary motor cortex) and area 3 (primary somatic sensory cortex) in Nissl-stained sections cut orthogonal to the course of the central sulcus. Although the positions of the cytoarchitectonic boundaries in the paracentral lobule showed considerable interindividual variation, the locations of the borders o f areas 4 and 3 along the course of the sulcus were similar among the 40 hemispheres examined. In addition to describing more thoroughly thi s portion of the human cerebral cortex, these observations provide a b asis for evaluating lateral symmetry of the human primary sensorimotor cortex.