How sensory cortex is subdivided in mammals: implications for studies of prefrontal cortex

A problem for studies of all cortex, including prefrontal cortex, is how to relate results to proposed subdivisions of the brain and how to compare results across species. Investigators have been highly dependent on traditional architectonic maps of neocortex. However, over the last 20 years, other methods, especially the microelectrode mapping method, have been applied to regions of sensory cortex, where orderly representations of receptor surfaces have provided strong evidence for new proposals of how cortex is subdivided. As a result, we can more reliably indicate functional subdivisions of cortex and identify valid homologies across species. Obtaining accurate maps of functional subdivisions of prefrontal cortex in a range of mammalian species is an important goal in that such maps are basic to interpreting other data. While microelectrode mapping methods may be more difficult to apply to prefrontal than sensory cortex, a range of useful anatomical and histochemical methods are available. Studies of sensory cortex suggest that all mammals have a few sensory areas in common, and that additional areas have evolved in some lines. One approach toward a better comparative understanding of frontal cortex might be to investigate the possibility that primary motor cortex, the supplementary motor area, and the frontal eye field are areas that exist in most or all mammals, and use these fields, when they can be clearly demonstrated, as reference areas for further studies on how frontal and prefrontal cortex is subdivided.