ABSTRACT
Sensory and motor systems in mammals consist of a number of interconnected representations (maps) of receptor surfaces or muscle movements. The details of the organizations of these maps have long been known to be mutable or plastic during the development of the nervous system, so that injuries to the receptor array and other forms of sensory deprivation alter the course of development and produce an abnormal system. Because such alterations were difficult or impossible to reverse in the mature brain, and manipulations that were effective in altering the developing brain failed to alter the mature brain, the prevailing assumption was that sensory and motor systems were highly stable after a period of developmental malleability. We now know that the sensory and motor maps of mature mammals are highly plastic in internal organization (see for review Kaas, 1996; Chino, 1997; Florence et al., 1997; Nudo et al., 1997; Buonomano and Merzenich, 1998). The removal of activating inputs through peripheral nerve or sensory tract damage can be followed by reactivations of deprived neurons in sensory systems so that these neurons acquire new receptive fields and altered response properties. Similar changes in neurons can be observed after lesions that partially damage central nuclei and cortical areas, and after injuries to motor nerves and structures.
