The Organization of Somatosensory Cortex in Primates and Other Mammals

Abstract

In pioneering studies on macaque monkeys, Marshall, Woolsey and Bard (1937) defined a region of postcentral parietal cortex that was responsive to stimulation of the body. The responsive region, which became known as the primary or first somatosensory region, S-I, contains four generally recognized architectonic fields, Areas 3a, 3b, 1, and 2. Since the original report of Marshall et al. (1937), there have been a number of interpretations of the significance of these four fields, and of the organization of the S-I region of primates (for recent examples, see Carlson et al., 1982; McKenna et al., 1982; Jones et al., 1978; Paul et al., 1972). In a series of papers, stemming from our first report on the organization of the S-I region in owl monkeys (Merzenich et al., 1978), my colleagues and I have argued that each of the four architectonic fields constitutes a functionally distinct area of somatosensory cortex. In the same sense that visual areas I and II (Areas 17 and 18) are functionally distinct and yet obviously interrelated, we postulated that each of Areas 3a, 3b, 1 and 2 contains a separate and parallel representation of the body; that Areas 3b, 1, and probably 2 are further distinguished by mirror reversals of somatopic order at their common borders, and that each Area has its own distinctive pattern of anatomical connections, neuron response types, and intrinsic organization.