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Spinal Cord Plasticity in the Acquisition of a Simple Motor Skill

  • Jonathan R. Wolpaw

Abstract

Studies of the plasticity underlying the acquisition of motor skills traditionally focus on supraspinal areas such as cerebral cortex and cerebellum. However, a large body of clinical and laboratory evidence indicates that substantial plasticity occurs in the spinal cord and that it plays an important part in skill acquisition. Operant conditioning of the spinal stretch reflex (SSR) or of its electrical analog, the H-reflex, is a simple example of such plasticity and provides a convenient laboratory model for defining the responsible mechanisms. The SSR and the H-reflex are mediated by a wholly spinal and largely monosynaptic pathway consisting of the la afferent fiber from the muscle spindle, its synapse on the spinal motoneuron, and the motoneuron itself. Monkeys, humans, and rats can gradually increase or decrease SSR or H-reflex amplitude when rewarded for doing so. Driven by task-appropriate change in descending influence from supraspinal structures, reflex change begins with a rapid change (phase I) in the first 1–2 days and then continues with gradual change (phase II) over weeks and months. Reflex change is accompanied by plasticity at multiple sites in the spinal cord. Plasticity occurs in motoneuron firing threshold and conduction velocity, in several different synaptic terminal populations on the motoneuron, and probably in interneurons as well. It also occurs contralaterally. The corticospinal tract is probably essential for producing this plasticity. While some changes, such as that in firing threshold, probably contribute to the rewarded behavior (primary plasticity), others may preserve previously learned behaviors (compensatory plasticity), or are activity-driven products of plasticity elsewhere (reactive plasticity). As these data and data from other simple vertebrate and invertebrate models illustrate, a complex pattern of plasticity is the necessary and inevitable outcome of even the simplest learning. Operant conditioning of the SSR and H-reflex appears to be similar to changes in spinal cord function that occur in early life and in the course of skill acquisition throughout life. The gradual development of this plasticity over the course of training is an important element in skill acquisition. The spinal cord is shaped by long-term descending influence so as to provide a substrate suited for execution of an individual’s entire roster of motor performances.

Keywords

Operant Conditioning Presynaptic Inhibition Experimental Brain Research Reflex Amplitude Spinal Cord Function 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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Copyright information

© Springer Science+Business Media New York 2001

Authors and Affiliations

  • Jonathan R. Wolpaw
    • 1
    • 2
  1. 1.Wadsworth CenterNew York State Department of HealthAlbanyUSA
  2. 2.State University of New YorkAlbanyUSA

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