 The neomammalian brains structure is of great complexity, and has evolved over time allowing humans to reach the top of the food chain.The neocortex is made up of grey matter consisting of folds to increase the surface area and memory retention, these folds in humans are 80% excitatory and 20% inhibitory.The arrangement of these folds differs from human to human, and is believed to account for the differing cognitive abilities of individual humans.