Cortical Columns Show Specificity for Modality and Location

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.

Figure 1  The Columnar Organization of the Somatosensory Cortex
The part of the somatosensory cortex shown here represents some of the fingers of the right hand. The different regions of somatosensory cortex—Brodmann’s areas 3a, 3b, 1, and 2—receive their main inputs from different kinds of receptors. Area 3b receives most of its projections from the superficial skin, including both fast-adapting and slow-adapting receptors; these projections are represented in separate cortical columns or slabs. Area 3a receives input from receptors in the muscle spindles. The cortex is organized vertically in columns and horizontally in layers. Input from the thalamus arrives at layer IV, where neurons distribute information up and down layers. (After Kaas et al., 1979.)

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.

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