What's all this fuss about the neocortex?
This idea of cortical folding leads us to consider the significance of the neocortex in general.
First of all, what is neocortex??? Neocortex is the structure in the brain that differentiates mammals from other vertebrates and it is assumed that the neocortex is responsible for the evolution of intelligence.
Is there a relationship between the amount of neocortex and brain size? More importantly, is there an increase in relative neocortical volume in some mammals? Relevant data have been provided by a number of authors (Macphail, Stephen, Harman) that there is within different mammalian orders a good correlation between brain size and both neocortical volume and neocortical surface. For example, there is a direct linear relationship between neocortical volume and brain volume in primates (see Figure 7.3 and 7.4, Macphail, 248). There are some slight differences between orders in that rodents have less relative neocortex than primates, carnivores, and ungulates, and that some types of opossums have even less than rodents.
What is the significance of these statements? First, it seems that man possesses no more neocortex than would be expected in a primate of that brain size. Second, although primates generally have more neocortex than some other mammals, they clearly are not unique in their neocorticalization.
Knowing the "role" (see above, or see glossary) of neocortex, one may be surprised that man and primates show so little superiority in terms of amounts of neocortex. It has often been assumed that the evolution of the neocortex is responsible for the evolution of intelligence. Yet, what happens when data about neocortex is collected or analyzed slightly differently? Let's look at another method of research and see if there is an effect on outcomes and conclusions about neocortical significance . . .