Title : Effect of stimulating the lumbar skin caudal to a complete spinal cord injury on

35 Sensory feedback is a potent modulator of the locomotor pattern generated by spinal 36 networks. The purpose of this study was to assess the effect of cutaneous inputs from the back on 37 the spinal-generated locomotor pattern. The spinal cord of six adult cats was transected at low 38 thoracic levels. Cats were then trained to recover hindlimb locomotion. During experiments, the 39 skin overlying lumbar vertebrae L2 to L7 was mechanically stimulated by a small calibrated clip 40 or by manual pinching. Trials without and with cutaneous stimulation were performed at a 41 treadmill speed of 0.4 m/s. Although manually pinching the skin completely stopped hindlimb 42 locomotion and abolished weight support, cutaneous stimulation with the calibrated clip 43 produced smaller effects. Specifically, more focalized cutaneous stimulation with the clip 44 reduced flexor and extensor muscle activity and led to a more caudal positioning of the paw at 45 contact and liftoff. Moreover, cutaneous stimulation with the clip led to a greater number of steps 46 with improper non-plantigrade paw placements at contact and paw drag at the stance-to-swing 47 transition. The most consistent effects on the hindlimb locomotor pattern were observed with 48 cutaneous stimulation at mid-lumbar levels, from L3-L5. The results indicate that cutaneous 49 stimulation of the skin modulates the excitability of spinal circuits involved in generating 50 locomotion and weight support, particularly at spinal segments thought to be critical for rhythm51 generation. 52 53