The somatosensory cortex of mammals has a number of subdivisions or processing areas. Although the number varies by species, each cerebral hemisphere in all mammals contains at least two systematic representations of the tactile receptors of the contralateral body surface, the primary somatic area SI, and the secondary somatic area SII. Neurons throughout these representations can be activated by stimuli on restricted portions of the body surface, the receptive fields of the neurons. These two representations have fairly consistent organizations from individual to individual within a species and conform to a general plan across species. Yet the organizations of the maps of the body surface can be altered in developing or adult mammals by removing or changing the significance of some of the inputs, or by damaging parts of maps. These changes in map organizations result from neurons losing their original receptive fields and...