The allocortex (also known as heterogenetic cortex) is one of the two types of cerebral cortex, the other being the neocortex. It is characterized by having just three or four cell layers, in contrast with the six layers of the neocortex, and takes up a much smaller area than the neocortex. There are three subtypes of allocortex: the paleocortex, the archicortex, and the periallocortex – a transitional zone between the neocortex and the allocortex.
|Anatomical terms of neuroanatomy|
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 in Brodmann area 4 that lacks granule cells.
The allocortex has three or four layers of neuronal cell bodies, in contrast to the six layers of the neocortex. There are three subtypes of allocortex, the paleocortex, archicortex and periallocortex.
Paleocortex is a type of thin, primitive cortical tissue that consists of three cortical laminae (layers of neuronal cell bodies). The two granular layers II and IV of neocortex are absent in paleocortex. The main areas of paleocortex are the olfactory bulb, olfactory tubercle and piriform cortex.
Periallocortex is a transitional form between neocortex and either paleo- or archi-cortex. It thus can be either peripaleocortex (anterior insular cortex) or periarchicortex (entorhinal cortex, presubicular cortex, retrosplenial, supracallosal, and subgenual areas).
Because the number of laminae that compose a type of cortical tissue seems to be directly proportional to both the information-processing capabilities of that tissue and its phylogenetic age, and also because olfaction is a major sensory modality in phylogenetically early animals, paleocortex is thought to be the most primitive form of cortex.
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- "Archicortex". BrainInfo. University of Washington. Retrieved 17 March 2017.