Versatile robotic interface to evaluate, enable and train locomotion and balance after neuromotor disorders

Central nervous system (CNS) disorders distinctly impair locomotor pattern generation and balance, but technical limitations prevent independent assessment and rehabilitation of these subfunctions. Here we introduce a versatile robotic interface to evaluate, enable and train pattern generation and balance independently during natural walking behaviors in rats. In evaluation mode, the robotic interface affords detailed assessments of pattern generation and dynamic equilibrium after spinal cord injury (SCI) and stroke. In enabling mode, the robot acts as a propulsive or postural neuroprosthesis that instantly promotes unexpected locomotor capacities including overground walking after complete SCI, stair climbing following partial SCI and precise paw placement shortly after stroke. In training mode, robot-enabled rehabilitation, epidural electrical stimulation and monoamine agonists reestablish weight-supported locomotion, coordinated steering and balance in rats with a paralyzing SCI. This new robotic technology and associated concepts have broad implications for both assessing and restoring motor functions after CNS disorders, both in animals and in humans.

Fig. Training enabled by the robotic postural neuroprosthesis restores equilibrated steering in rats with a severe SCI. (A) Schemes depicting experimental testing paradigm and conventions to compute body angles. Rats were positioned quadrupedally in the robotic interface, which provided constant-force vertical support while delivering zero force in all the other directions. The rats walked along a 90°-curved runway. Trunk orientation was measured as the angle between the pelvis and the orientation of the upper body velocity vector, termed heading, which also defined the locomotor trajectory. (B) Schemes depicting the SCI, as well as the electrical and pharmacological stimulations for enabling locomotor states. (C) Successive positions of the trunk at swing onset, locomotor trajectory and velocity (arrow’s length) of trunk motion as well as direction of upper body motion (arrow) during a representative trial performed before the lesion and at 60 d after lesion for a nontrained and a trained rat. The bottom plots show the superimposed locomotor trajectories extracted from all the trials of all the rats. The density distribution of locomotor trajectories (all trials and rats) is shown in the top left corner of each plot. (D) Averaged (all rats, ± s.d.) distance between locomotor trajectories and the optimal trajectory computed from all the prelesion trials (n = 9 rats). The shaded area indicates the progression along the curved section of the runway. (E) Averaged distance between each locomotor trajectory and the optimal trajectory. (F) Maximum deviation of the pelvis segment with respect to the heading vector. Error bars, s.e.m. **P < 0.01 from all the other nonmarked conditions.