Deficits in severe spinal cord injury (SCI) are the result of disconnection between supraspinal motor control centers and the local lumbar spinal circuits necessary to produce voluntary leg movement. Promising studies in both animals and humans with severe SCI have shown that lumbar electric epidural stimulation (EES) can restore the ability to stand and perform coordinated complex locomotion. However, the exact mechanism by which such stimulation may restore lower-limb function remains poorly understood. Moraud et al1 recently published an article in Neuron using both computational and experimental models of gait and locomotion to elucidate the mechanisms by which EES can restore lower-limb motor function. They showed that EES interacts primarily with muscle spindle feedback circuits to elicit muscle activity in the specific patterns necessary to achieve locomotion.The authors first developed a dynamic computational model that coupled spinal neural firing patterns to the biomechanics of the rat hind limb. The model incorporated information on the output of S alpha motor neurons, excitatory and inhibitory interneurons, and input from group Ia and group II afferent fibers.
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