A re-evaluation of rat frontal cortex suggests that the medial frontal cortex, usually considered to homologous to the dorsolateral prefrontal cortex of primates, actually consists of cortex homologous to primate premotor and anterior cingulate cortex. The lateral MD-projection cortex of rats resembles portions of primate orbital cortex. If prefrontal cortex is construed broadly enough to include orbital and cingulate cortex, rats can be said to have prefrontal cortex. However, they evidently lack homologues of the dorsolateral prefrontal areas of primates. This assessment suggests that rats probably do not provide useful models of human dorsolateral frontal lobe function and dysfunction, although they might prove valuable for understanding other regions of frontal cortex.
Galagos are prosimian primates with relatively small brains and very small frontal lobes.
We found that galagos, like monkeys, possess a discrete region of frontal cortex with a well-developed internal granular layer. This region was tiny however, and while it contained cortex that resembled the frontal eyefield, we could find no region of galago cortex that had the distinctive connectional and architectonic characteristics of principalis cortex. Of course, the dorsolateral PFC receives a particularly strong MD projection, but so does cingulate and orbital cortex. Thus, MD projections are not diagnostic of dorsolateral prefrontal cortex. This region receives dense inputs from MD and from the dopamine-containing nuclei of the brainstem.