Endpoint force patterns evoked by intraspinal stimulation-ipsilateral and contralateral responses

We studied the mapping and structure of endpoint forces produced by microstimulation of the cat spinal cord. The forces evoked by microstimulation varied in magnitude and direction as a function of limb configuration. At some stimulation sites, the force patterns exhibited a point of convergence where the net endpoint force was zero. Ipsilateral stimulation in the dorsal aspect of the cord evoked flexion responses that exhibited a convergent point, while extension responses evoked by ipsilateral stimulation were not convergent. Conversely, contralateral stimulation in the dorsal aspect of the cord evoked extension responses that exhibited a convergent point, while flexion responses evoked by contralateral stimulation were not convergent. Stimulation in the ventral aspects of the cord, as well as intramuscular stimulation of single muscles did not produce convergent force patterns. The results demonstrate that stimulation in the dorsal and intermediate aspects of the spinal cord can generate organized, convergent force patterns, while stimulation in the ventral aspect of the cord can not. These results suggest that electrical activation of higher-order neurons may be used to coordinate the activation of the multiple muscles required in multi-joint movements