Fig 3. Intraoperative images of the brain tumor outlined by sonography and demarcated on the surface by letters A, B, and C. The postcentral gyrus extending anteriorly to approximate the posterior border of the middle frontal gyrus, hiding the superior-lateral portion of the precentral gyrus from view, is notable. Electrocortical stimulation of the upper precentral gyrus (position 5) resulted in proximal upper-extremity movement. Electrocortical stimulation at positions 1, 2, 3, and 11 within the anterior aspect of the postcentral gyrus resulted in hand movements. Electrocortical stimulation at positions 8 and 10 in the posterior aspect of the postcentral gyrus resulted in right-hand numbness. Stimulation at position 7 within the postcentral gyrus involved by the tumor resulted in a reproducible abnormal sensation of the upper back. T, tumor beneath visible cortex.