The cerebral cortex is organized into vertical columns of neurons, with each column having a particular functional significance. In pioneering work begun in the 1950s, Vernon Mountcastle (1984) mapped the receptive fields of individual neurons in somatosensory cortex using microelectrodes.
Mountcastle found that each cortical cell not only has a precise receptive field, but also responds to only one submodality. For example, some cells respond only to a light touch, and others respond only to deep pressure. Furthermore, within a given column of neurons, all the cells respond to the same location and quality of stimulation. Cells in a band of columns respond to the same quality of stimulation, and another band of columns is devoted to another kind of stimulation, as Figure 1 illustrates.
Each column extends from the surface of the cortex (layer I in the figure) down to the base of the cortex (layer VI). Each type of receptor feeds information to a different cortical column. Moving the stimulation to a slightly different region on the skin shifts the excitation to a different cortical column. Thus, the columns code for both location and quality of stimulation.
Kaas, J. H., Nelson, R. J., Sur, M., Lin, C. S., et al. (1979). Multiple representations of the body within the primary somatosensory cortex of primates. Science 204: 521–523.
Mountcastle, V. B. (1984). Central nervous mechanisms in mechanoreceptive sensibility. In I. Darian-Smith (Ed.), Handbook of physiology, Section 1: Vol. 3. Sensory processes (pp. 789–878). Bethesda, MD: American Physiological Society.