Title: Incomplete Spinal Cord Injury Promotes Durable Functional Changes within the Spinal 1 Locomotor Circuitry 2 Groupe De Recherche Sur Le Système Nerveux Central (frsq) And

32 While walking in a straight path, changes in speed result mainly from adjustments in the 33 duration of the stance phase while the swing phase remains relatively invariant, a basic feature of 34 the spinal central pattern generator (CPG). To produce a broad range of locomotor behaviors, the 35 CPG has to integrate modulatory inputs from the brain and the periphery and alter these 36 swing/stance characteristics. In the present work we raise the issue as to whether the CPG can 37 adapt or reorganize in response to a chronic change of supraspinal inputs, as it is the case after 38 spinal cord injury (SCI). Kinematic data obtained from 6 adult cats walking at different treadmill 39 speeds were collected to calculate the cycle and sub-phases duration at different stages after a 40 first spinal hemisection at T10 and after a subsequent complete SCI at T13 respectively aimed at 41 disconnecting unilaterally and then totally the spinal cord from its supraspinal inputs. The results 42 show, first, that the neural control of locomotion is flexible and responsive to a partial or total 43 loss of supraspinal inputs. Second, we demonstrate that a hemisection induces durable plastic 44 changes within the spinal locomotor circuitry below the lesion. In addition, this study gives new 45 insights into the organization of the spinal CPG for locomotion such that phases of the step cycle 46 (swing, stance) can be independently regulated for adapting to speed and also that the CPGs 47 controlling the left and right hindlimbs can up to a point be regulated independently. 48 49