Figure 1.

Experimental design. A, The experimental box was divided into two corridors, each 2.5 m long and 0.5 m wide. The corridors were partially separated by a barrier (gray), and one corridor contained a horizontal ladder. Cats were trained to pass sequentially and repeatedly through the corridors. Open circles on the crosspieces of the ladder schematically show placements of cat forelimbs. B, A scheme of the recording area within the forelimb representation of the left motor cortex. The microelectrode entry points into the cortex (cortical plate openings through which penetrations have been made) were combined from all cats and are shown by black circles. Cru, Cruciate sulcus; Pcd, post cruciate dimple). C, Types of neurons recorded: CT6, corticofugal neurons of layer VI projecting to VL; CT5, corticofugal neurons of layer V that project to VL or to VL and the PT. The neurons were identified by their antidromic responses to electrical stimulation of the corresponding structures (Stim 1, Stim 2). MC, Motor cortex. D, Photomicrograph of a section through the motor cortex, stained with cresyl violet. Layers of the cortex are numbered, and layer V is outlined by dashed lines. Note the clusters of giant cells that are characteristic of layer V. An arrow points to the microlesion made in the upper layer VI in the awake animal using the criteria outlined in Materials and Methods.