Introduction

The traditional view of the spinal cord

A major feature of neuroscience over the past 30 years has been the steadily growing recognition of the ubiquity of activity-dependent plasticity in the central nervous system (CNS). Recognition of the multiple mechanisms of synaptic and neuronal plasticity, of their existence in many different regions, and of the frequency with which they are activated, has wholly overturned the traditional view of a hardwired CNS that stores the effects of past experience by a limited set of mechanisms and only in a few specialized places. This new understanding, however, still focuses mainly on the brain, and excludes, intentionally or otherwise, the spinal cord. As late as the 18th century, the spinal cord was seen as simply a big well-protected nerve through which the brain interacts with the world; and it is still commonly assumed to be merely a stable way station between the brain and the periphery, the repository of nothing more than a few fixed reflexes. The original rationale for this 19th-century assumption was as much theological as scientific (reviewed in Wolpaw and Tennissen, 2001). Nevertheless, it remains embedded in neuroscientific theory and research. Activity-dependent plasticity, or persistent CNS modification that results from past experience and affects future behavior, is still considered by many neuroscientists to be a purely supraspinal capacity.

The recognition of spinal cord plasticity

It is now abundantly clear that the spinal cord possesses capacities for activity-dependent plasticity comparable to those found elsewhere in the CNS.