Robotic training and spinal cord plasticity.

What is the potential for recovery of locomotor ability after a spinal cord injury? Both human and animal studies show that the spinal cord has the potential to reorganize and/or readjust to the loss of supraspinal input and utilize the remaining peripheral input to actually control stepping and standing. Motor training can be used to provide sensory ensembles within the spinal circuitry that are task-specific, i.e., step training improves stepping and stand training improves standing. A large component of this learning is a function of improved coordination of motor pools within and among limbs. The most successful type of training includes variability in the performed task, i.e., monotonous repetition of the exact same sensorimotor pattern results in "learned disuse". The use of robotics for training specific motor tasks has become more prevalent recently and we report here that using an "assist-as-needed" approach for step training after a severe spinal cord injury provides a high probability of successful rehabilitation. The "assist-as-needed" paradigm allows variability in the step trajectory within specific boundaries such that the robotic arms constrain the deviations in a manner mimicking that observed under normal, intact conditions. Another critical feature of robotic devices or step training seems to be the ability to integrate normal hip and leg motion as occurs during normal stepping. These types of robotic devices have the potential to aid therapists in the clinical setting and to enhance the ability of spinal cord injured individuals to regain the maximum locomotor ability possible.