six-layered structure characteristic of isocortex. The main peripaleocortex area is anterior insular cortex.

Peripaleocortex does not histologically transit directly to the true isocortex. Instead, at borders between peripaleocortex and isocortex, there are other transitional areas from the isocortex side, called proisocortex. Thus, at borders between paleocortex and isocortex, there are two transitional areas. One transitional area, which is anatomically located