Taking the measure of diversity: Comparative alternatives to the model-animal paradigm in cortical neuroscience

Cortical neuroscience is founded on studies of a very few model organisms, mainly rats, cats, and macaque monkeys. The concentration of effort on such a few species would be defensible if cortical organization were basically uniform across mammals, as is commonly believed. Although there is little r eason to doubt that some features of cortical organization are indeed wides pread among mammals, phyletic variation in cortical organization is far mor e extensive than has generally been appreciated or acknowledged. Rats, for example, differ from other mammals in the generics and chemistry of their c ortical neurons, in connectivity and areal organization, and in the functio ns of specific cortical regions. Likewise, macaque monkeys, although widely used as models of the human visual system, lack a number of features found in human visual cortex. Given the variability of cortical organization, ho w should neuroscientists approach the study of nonhuman species, and what c an we reasonably expect to learn from them? First, by examining a wider ran ge of species than are currently employed, and by using modern techniques o f phyletic analysis, neuroscientists can more rigorously identify those fea tures of cortical organization that are, in fact, widely shared among mamma ls or among particular mammalian subgroups. Second, by taking account of va riations, neuroscientists can abstract more reliable and general principles of structure-function relationships in the nervous system. Finally freed f rom the doctrine of basic uniformity, neuroscientists can pursue the study of human cortical specializations, and so advance our understanding of what distinguishes humans as a biological species. Copyright (C) 2000 S. Karger AG. Basel.