Scientific basis of spasticity: Insights from a laboratory model

A variety of central nervous system injuries, diseases, and developmental d eficits can lead to motor disorders that present complex mixtures of sympto ms. Those that have a fundamental similarity characterized by the appearanc e of exaggerated velocity-dependent resistance to the lengthening of skelet al muscles are called spasticity. Reports based on clinical observations of motor disorders have and continue to provide the essential database of inf ormation regarding the range and distribution of unifying and discordant fe atures of spasticity. Laboratory investigations employing animal models of motor disorders following experimental lesions of the central nervous syste m have reproduced some of the neurophysiologic changes that accompany injur y of the central nervous system in humans. Those experimental lesions produ ced by spinal cord contusion/compression reproduce many of the histopatholo gic features displayed in traumatic injury of the human spinal cord as well . Studies using this model have revealed not only changes in reflex thresho ld and amplitude but also alterations in fundamental rate-modulation proces ses that regulate reflex excitability during repetitive stimulation. This r eport characterizes insights obtained from a laboratory investigation in se arch of fundamental mechanisms that contribute to the development of spasti city and provides a vantage point for understanding therapeutic strategies for treatment of spasticity.