Figure 2. Areas of the motor cortex studied.

A: Areas of recording within representations of the fore- and hindlimb in the left motor cortex. Microelectrode entry points are combined from cat 1 (circles), 2 (diamonds), and 3 (squares) and shown by white (forelimb-related neurons in the track) or black (hindlimb-related neurons in the track) symbols on a photograph of cat 9 2 cortex. Arrows indicate approximate medio-lateral positions of parasagittal sections show in D–G. B: The method of insertion and advancement of electrodes into cortex. A microelectrode (2) is manually inserted in one of openings in the plastic plate (1) implanted into skull; and is then soldered to an arm (3) of a micromanipulator (4). In this manually driven micromanipulator, one revolution of the screw results in 200 μm advancement of the electrode. C: Collision test determines whether a PTN response is antidromic. Top trace, a PTN spontaneously discharges (arrow 1), and pyramidal tract neuron is stimulated ~5 ms later (arrow 2). PTN responds with a latency ~1 ms (arrow 3). Bottom trace, a PTN spontaneously discharges (arrow 1) and pyramidal tract is stimulated ~0.5 ms later (arrow 2). The PTN does not respond (arrow 3) because in 0.5 ms its spontaneous spike was still en route to pyramidal tract, and thus collision/nullification of spontaneous and evoked spikes occurred. D: Drawing of a parasagittal section through the rostral bank of the cruciate sulcus (CRU). The reference track made with a thick electrode is shown by a tilted line and the position of the reference electrolytic lesion is shown by a black circle. The square approximately indicates the area shown in the photomicrograph in E. E, Photomicrograph of a parasagittal section through the motor cortex, stained with cresyl violet. Layers of the cortex are numbered. Clusters of giant cells in layer V that are characteristic for area 4γ are visible around the lesion. Arrows point to a track made by a microelectrode. Arrowheads point to the reference electrolytic lesions. F: Drawing of a parasagittal section through the caudal bank of the cruciate sulcus. The position of the reference electrolytic lesion is shown by a black circle. The square approximately indicates the area shown in the photomicrograph in G. G, Photomicrograph of a parasagittal section through the motor cortex, stained with cresyl violet. Layers of the cortex are numbered. An arrowhead points to the reference electrolytic lesion. Clusters of giant cells in layer V that are characteristic for area 4γ are visible around the lesion. Scales in D–G were not corrected for shrinkage of tissue during processing. H: An example recording of a neuron along with 4 movement sensors for four limbs (F-R – right forelimb, F-L – left forelimb, H-R – right hindlimb, H-L – left hindlimb), and 4 muscles (Tric-R – right triceps, Tric-L – left triceps, Glut-R – right gluteus, Glut-L – left gluteus) during quadrupedal locomotion.