| Functional motion and control of limbs paralyzed after spinal cord injury or stroke can be restored by using electrodes implanted within the body. Unfortunately, not many motor prostheses have been established as standard devices for restoring functional limb movement. Direct stimulation of the neuromuscular junction is most commonly used. However, nerve trunk, spinal cord and spinal roots are other feasible control sites. From the viewpoint of understanding neural mechanisms toward more graceful control of limb movement, this thesis focused on the general role played by the spinal cord, the biomechanics of multiarticulated limb, and sensorimotor regulation by first order sensory neurons.; Muscle, nerve and spinal cord stimulation generated selective movements in all directions. Ventral and dorsal roots only elicited extension and flexion responses respectively. Muscle stimulation produced the most smoothly graded recruitment curves, but required an order of magnitude more current. The evidence for the existence of 4 or 5 clear 'primitives', originally suggested using frogs, was not verified in the mammalian spinal cord. However, a noteworthy finding was that the intermediate gray matter contains some rostrocaudal and ventrodorsal localization (but not complete modules) that would produce coordinated synergies. Movement elicited by simultaneous stimulation of multiple sites did not follow the linear summation of the vectors produced by stimulating individual sites, but tended to converge to an equilibrium point, suggesting that musculoskeletal properties play an important role in determining the trajectory. These principles should allow a more rational choice of stimulation site to restore particular functions in paralyzed human subjects.; A high-density, intrafascicular microelectrode array implanted in the sciatic nerve permitted more selective stimulation with more graded recruitment of individual muscles in chronic cats than was achieved by conventional cuff electrodes. The microelectrode arrays simultaneously recorded from over 100 sensory neurons in dorsal root ganglia in anesthetized cats. The activity of many neurons was correlated with the position of the foot and the activity in a population of neurons can be used to predict this position accurately. These methods may be useful for developing advanced prosthetic devices in which sensory information is used in a feedback control system. |
