Does Functional Recovery Imply Stable Circuitry in the Spinal Animal?

Spinal animals can regain locomotor function through gait training. However, the neural processes involved in this recovery are poorly understood. Here we use computer simulation to address if the reorganization of spinal circuits associated with the functional recovery leads to meaningful, stable circuitry function. Specifically, we develop a neuromuscular model of a spinalized rat whose circuitry can adapt based on two alternative Hebbian learning strategies, one designed to guide the circuitry back to its normal pre-injury state and the other designed to destabilize it and drive it into saturation. Exposing the model to simulated gait training, we find that both strategies lead to recovery of locomotor function as defined by the outcome measures reported in studies with spinal rats. If anything, the results obtained with the destabilizing learning strategy seem to agree more with animal observations, since it produces similarly excessive amplitudes in muscle activity. Our results suggest that gait training of spinalized animals does not necessarily effect a meaningful recovery of their spinal circuitry function. More experimental work should be directed to clarify this point, as it may have grave implications for the potential of gait rehabilitation in patients with motor complete injuries of the spinal cord.