Allocortex

The allocortex (from Latin allo-, meaning other, and cortex, meaning bark or crust), or heterogenetic cortex, and neocortex are the two types of cerebral cortex in the brain. In the human brain, the allocortex is the much smaller area of cortex taking up just 10%; the neocortex takes up the remaining 90%.^[1] It is characterized by having just three or four cortical layers, in contrast with the six cortical layers of the neocortex. There are three subtypes of allocortex: the paleocortex, the archicortex, and the periallocortex—a transitional zone between the neocortex and the allocortex.^[2]

The specific regions of the brain usually described as belonging to the allocortex are the olfactory system and the hippocampus.

Allocortex is termed heterogenetic cortex, because during development it never has the six-layered architecture of homogenetic neocortex. It differs from heterotypic cortex, a type of cerebral cortex, which during prenatal development, passes through a six-layered stage to have fewer layers, such as the agranular cortex such as Brodmann area 4 that lacks granule cells.^[3]