Lateral views of the hemispheres of M1 (a) and M4 (b). (c,d) Coronal sections taken at the level of the recorded regions, as indicated by the dashed line in (a,b). Low-power photomicrographs show higher magnification views of a Nissl-stained coronal section. Arrows indicate tracks of probe penetrations where visuomotor grasping neurons were recorded. For the sake of comparison, the data of M4 (left hemisphere) are shown as a right hemisphere. CS, central sulcus; IAS, inferior arcuate sulcus; IPS, intraparietal sulcus; LS, lateral sulcus; PS, principal sulcus; SAS, superior arcuate sulcus; Spur of the arcuate sulcus; STS, superior temporal sulcus.