The connectional organization of neural systems in the cat cerebral cortex

BACKGROUND The mammalian brain consists of the cerebral cortical sheet, which is composed of many distinct areas, the cerebellar cortex, and many non-cortical nuclei. Powerful neuroanatomical techniques have revealed a large number of connections between these structures. The large number of brain structures and the very many connections between them form a strikingly complex network. The complexity of this network has made it difficult to understand how the central nervous system is organized. Recently, however, optimization analysis of an important subset of central nervous connections that occur between the different areas of the cerebral cortex has produced understandable and quantitative representations of the organization of cortical systems of the primate brain. RESULTS Here we briefly report the extension of this approach to the cortical systems of the cat. There were four connectional clusters of cortical areas in the cat. These clusters of areas corresponded to the visual, auditory, and somato-motor systems, and to the frontal and limbic areas, which we call the fronto-limbic complex. All the major sensory systems were hierarchically organized, and their 'higher' stations were more closely associated with the fronto-limbic complex than were their 'lower' stations. CONCLUSIONS Features of the organization of the cat brain, together with earlier primate results, suggest that there may be a common cortical plan in mammals. We suggest that this common plan may involve relatively discrete, hierarchically organized, cortical sensory systems and a topologically central fronto-limbic complex. Specific variations on this wiring plan may relate to evolutionary history and selection for particular ecological niches.