An animal model of functional electrical stimulation: evidence that the central nervous system modulates the consequences of training

Study Design:Review of how spinal neurons can modulate the consequences of functional electrical stimulation (FES) in an animal model.Methods:Spinal effects of FES are examined in male Sprague–Dawley rats transected at the second thoracic vertebra. The rats are exposed to FES training 24–48 h after surgery. Experimental manipulations of stimulation parameters, combined with physiological and pharmacological procedures, are used to examine the potential role of spinal neurons.Results:The isolated spinal cord is inherently capable of learning the response–outcome relations imposed in FES training contingencies. Adaptive behavioral modifications are observed when an outcome (electrical stimulation) is contingent on a behavioral response. In contrast, a lack of correlation between the response and outcome in training produces a learning deficit in the spinal cord, rendering it incapable of adaptive learning for up to 48 h. The N-methyl-D-aspartic acid receptor appears to mediate both the adaptive plasticity and loss of plasticity, seen in this spinal model.Conclusion:The behavioral effects observed with FES therapies are not simply due to the direct (motor) consequences of stimulation elicited by the activation of efferent motor neurons and/or selected muscles. FES training has the capacity to shape inherent spinal circuits and to produce a long-lasting behavioral modification. Further understanding of the spinal mechanisms underlying adaptive behavioral modification will be integral for establishing functional neural connections in a regenerating spinal system.