Plastic changes in the central nervous system are associated with hyperacti
vity, hypersensitivity, and spread of activity including activation of brai
n regions that are not typically involved. Symptoms and signs such as neuro
pathic pain and tinnitus and hyperactive disorders such as muscle spasm and
synkinesis may result from such changes in function. Plastic changes that
cause symptoms of diseases can be initiated by novel stimulations, overstim
ulation, or deprivation of input and the induced changes in the function of
central nervous system structures may persist and aggravate after these ev
ents have ceased if the condition is not reversed. Disorders that are cause
d by neural plasticity are potentially reversible with treatment. However,
the absence of morphologic abnormalities makes diagnosis of these condition
s difficult and their treatment has been hampered by lack of understanding
of their pathophysiology. Here the role of neural plasticity in the pathoph
ysiology of several disorders is reviewed.