Neuromechanical strategies for obstacle negotiation during overground locomotion following an incomplete spinal cord injury in adult cats

Abstract

Following incomplete spinal cord injury in animals, including humans, substantial locomotor recovery can occur. However, functional aspects of locomotion, such as negotiating an obstacle remains challenging. We collected kinematic and electromyography data in ten adult cats before and at weeks 1-2 and 7-8 after a lateral mid-thoracic hemisection while they negotiated obstacles of three different heights. Intact cats always cleared obstacles without contact. At weeks 1-2 after hemisection, the ipsilesional hindlimb contacted obstacles in ~50% of trials, triggering a stumbling corrective reaction or lack of response. When complete clearance occurred, we observed exaggerated ipsilesional hindlimb flexion when it crossed the obstacle with the contralesional limbs leading. At weeks 7-8 after hemisection, complete clearance increased in favor of absent responses while the proportion of stumbling corrective reactions remained relatively the same. We found redistribution of weight support after hemisection, with reduced diagonal supports and increased homolateral supports, particularly on the contralesional side. The main neural strategy for complete clearance in intact cats consisted of increased activation of muscles that flex the knee. After hemisection, knee flexor activation remained but it was insufficient or more variable as the limb approached the obstacle. Intact cats also increased their speed when stepping over an obstacle, an increase that disappeared after hemisection. The increase in complete clearance over time after hemisection paralleled the recovery of muscle activation patterns or new strategies. Our results suggest partial recovery of anticipatory control through neuroplastic changes in the locomotor control system.