Role of Motor Cortex in Control of Locomotion

1. The activity of 252 motor cortex (MC) neurons (including 70 pyramidal tract neurons) was recorded extracellularly in the cat by means of a mobile electrode during free locomotion in a box. 2. The activity of 89% MC neurons was modulated during locomotion. The modulation was related to the stepping movements, since it increased in one stepping phase and decreased in the next. 3. MC neurons were also studied while the animal moved up a flat inclined surface, walking at different speeds, with a load of 85g attached to each forelimb, when the cat had to perform snakelike movements (turns) or walk on the flat surface placed in a horizontal plane. The pattern of MC neuron activity changed little under these conditions in comparison with uncomplicated locomotion. 4. The activity of 68 neurons was recorded in experiments with barriers and involving locomotion on a horizontal ladder which restricted the possible paw positions along the direction of locomotion. These tasks greatly affected the MC activity. 5. Neither bilateral MC lesion nor tetrodotoxin inactivation hampered uphill locomotion, walking along a moving floor, or locomotion involving turns and loaded forelimbs. On the contrary, it proved to be necessary for the MC to be intact for locomotion with space linked stepping limb movements (i.e. with barriers, on a ladder) to be possible. 6. Bilateral destruction of the ventrolateral nucleus of the thalamus (VL) resulted in a decrease in the rhythmical modulation of MC neurons during locomotion. After VL lesion the cat could walk quite well on the horizontal surface and uphill, at various speeds, with the forelimbs loaded; it could perform turns and could walk on the moving floor. The cat proved to be incapable, however, of walking with barriers and on the ladder.