The regions of the neocortex connect to each other via bundles of nerve fibers that travel under the neocortex, the so-called white matter of the brain. By carefully following these nerve fibers, scientists can determine how many regions there are and how they are connected. It is difficult to study human brains, so the first complex mammal that was analyzed this way was the macaque monkey. In 1991, two scientists, Daniel Felleman and David Van Essen, combined data from dozens of separate studies to create a famous illustration of the macaque monkey’s neocortex.
