In older species, such as fish, the archipallium makes up most of the cerebrum.

[2] Because the number of cortical layers that make up a type of cortical tissue seems to be directly proportional[clarification needed] to both the information-processing capabilities of that tissue and its phylogenetic age, the archicortex is thought to be the oldest and most basic type of cortical tissue.

[3] The archicortex is most prevalent in the olfactory cortex and the hippocampus,[4] which are responsible for processing smells and forming memories, respectively.

[7] Archicortical precursor cells are also present in the dentate gyrus of the developing mammalian embryo.

[9] Unlike the neocortex, current theories of the archicortex argue that it performs simple memorization without changing the input's format in any complex manner.