Influence of pyramidotomy on limb flexion movements induced by cortical stimulation and on associated postural adjustment in the cat.

Flexion movements induced by cortical stimulation and the associated postural adjustments in bilaterally pyramidotomised cats have been studied by means of an apparatus which measures separately the changes of force under each limb in the upright position of the animal. The results show: (1) The general motor behaviour of the animal is not affected by the lesion. The principal deficit is loss of tactile placing reaction in the forelimbs; there also appears a state akin to a vestibular syndrome when a light restraining harness is placed around the back and chest. (2) Stimulation of the motor cortex continues to evoke flexion movements of the contralateral limbs together with associated postural adjustment. Coordination between movement and postural adjustment is generally similar to that observed before pyramidal section, and response thresholds are unchanged. (3) Measurements reveal great quantitative modification both of the movement and the postural adjustment after the lesion. Weight shift latencies are increased and more dispersed in time, while the weight shifts themselves are reduced in amplitude and speed. (4) All these changes are more marked in the case of forelimb, rather than hindlimb, flexion, emphasising the greater degree of pyramidal influence on forelimb activity in the normal animal. (5) The results as a whole underline the ability of non-pyramidal systems, under the control of the motor cortex, to bring about both limb flexion and the associated postural adjustments in the absence of the corticospinal pathway.