The allocortex is the most primitive part of the cerebrum. It is located on the inferior surface of the cerebral cortex and it is a very small area in relation to the cortex as a whole. Unlike the neocortex (or isocortex), which is composed of a six-layered structure, the allocortex has three layers of nerve cells and neuroglia. Since it is a primeval part of the brain, its function is linked to emotion and emotion-related long-term memory and sense of smell.
The allocortex consists of the archicortex, periarchicortex, hippocampus, paleocortex, and olfactory tract and bulb. The paleocortex is the part of the allocortex from which the olfactory tract extends forwards to connect with the olfactory bulb, which contains mitral cells. The olfactory tract is a band of myelinated nerve fibers which send smell sensory information picked up by the mitral cells in the bulb to the paleocortex and amygdala. The archicortex, on the other hand, constitutes the three cortical layers of the hippocampus, which lies in turn deep within the temporal lobe.
Below, the inferior surface of the cerebrum, showing the different parts that make up the allocortex, which is phylogenetically the oldest portion of the cerebral cortex. Hippocampus cannot be seen as it lies within the archicortex.
