Operant Conditioning of Spinal Cord Reflexes in Rats

The H-reflex, the electrical analog of the spinal stretch reflex (SSR) is mediated largely by a wholly spinal, primarily two-neuron pathway. Because this pathway is influenced by descending pathways from the brain, these spinal reflexes can be operantly conditioned. Motivated by a paradigm in which reward depends on reflex size, monkeys, humans, rats, and mice can gradually increase or decrease the SSR or the H-reflex. The reflex change develops gradually over weeks and involves neuronal and synaptic plasticity at multiple sites in the spinal cord and the brain. This simple learning phenomenon is important both as a basic science model and as the basis for a new approach to restoring useful function after spinal cord injury or in other disorders. As a basic science model, it provides access to the locations, mechanisms, and behavioral impact of the complex plasticity associated with acquisition and maintenance of even the simplest motor skills, and it offers a unique opportunity to study the role of corticospinal tract activity in health and disease. As a new therapeutic approach to spinal cord injury or other neuromuscular disorders, it offers the opportunity to target each person’s specific functional deficits and to produce pathway-specific changes designed to ameliorate these deficits and restore more effective motor function. This article describes the methodology of H-reflex conditioning in the laboratory rat. The conditioning protocol described here is comparable in its key features to the reflex conditioning protocols that have proved effective in monkeys, mice, and humans.