Cortical mapping demonstrates human somatosensory gyrus is larger than motor gyrus

Abstract Craniotomy with intraoperative rolandic cortical mapping was used to evaluate and compare the relative exposed surface areas of somatosensory gyri (SSG) and motor gyri (MG). The records of patients who underwent intraoperative photography and electrophysiologic mapping of SSG and MG were reviewed. Patients were excluded if the perirolandic area was involved with tumor or if the operative exposure did not permit adequate visualization of perirolandic cortex. Twenty-five patients (10 females, 15 males, median age 31 years) with varying pathologies met these criteria. Twenty of the 25 craniotomies were performed on the left side. Outlines of the exposed SSG and MG were traced on transparencies, which were then digitized. The areas of the exposed surfaces of SSG and MG were computed in pixels. A ratio (S/M = surface area of exposed SSG/surface area of exposed MG) was computed for each patient. S/M was >1 (surface area of the SSG was larger than the surface area of MG) in 19 of 25 patients (76%). S/M ranged from 0.79 to 1.62 (median 1.18). These data indicate that the exposed surface area of SSG is usually larger than MG ( p