Neuromodulation of evoked muscle potentials induced by epidural spinal cord stimulation

32 Epidural stimulation of the lumbosacral spinal cord has been used to facilitate standing and 33 voluntary movement after clinically motor complete spinal cord injury. It seems of importance to 34 examine how the epidurally evoked potentials are modulated in the spinal circuitry, and 35 projected to various motor pools. We hypothesized that chronically implanted electrode arrays 36 over the lumbosacral spinal cord can be used to functionally assess spinal circuitry linked to 37 specific motor pools. The purpose of this study was to investigate the functional and topographic 38 organization of compound evoked potentials induced by the stimulation. Three individuals with 39 complete motor paralysis of the lower limbs participated in the study. The evoked potentials to 40 epidural spinal stimulation were investigated after surgery in supine position, and in one 41 participant during both supine and standing with body weight load of 60%. The stimulation was 42 delivered with intensity from 0.5 to 10V at a frequency of 2Hz. Recruitment curves of evoked 43 potentials in knee and ankle muscles were collected at three localized and two wide-field 44 stimulation configurations. Epidural electrical stimulation of rostral and caudal areas of lumbar 45 spinal cord resulted in a selective topographical recruitment of proximal and distal leg muscles, 46 as revealed by both magnitude and thresholds of the evoked potentials. Epidural stimulation 47 activated both afferent and efferent pathways. The components of neural pathways that can 48 mediate motor evoked potentials were highly dependent on the stimulation parameters and 49 sensory conditions, suggesting a weight-bearing induced reorganization of the spinal circuitries. 50