[Neuronal plasticity exemplified by the somatosensory system].

The mammalian brain is capable of a substantial functional reorganization, manifesting on a cortical somatotopical and on a behavioral level. Possible mechanisms are reviewed based on the work by others and ourselves on somatosensory reorganization in humans. The somatosensory system is characterized by divergent projections from the periphery to the cerebral cortex. Changes in synaptic weights allow for reorganization of sensory processing: On one side, limb amputation will result in a representational "invasion" of the differentiated cortex from neighboring regions with concomitant perceptual changes. On the other side, sensorimotor training can increase the representational cortical zone of a limb. Plastic changes can be temporary or persistent. Modulating factors like pain and certain drugs seem to induce a permissive state in the cortex resulting in enhanced reorganization. Thus, specific physical training combined with pharmacoceutical modulation holds promise to improve functional recovery after brain lesions.