The allocortex or heterogenetic cortex, and

neocortex The neocortex, also called the neopallium, isocortex, or the six-layered cortex, is a set of layers of the mammalian cerebral cortex involved in higher-order brain functions such as sensory perception, cognition, generation of motor commands, ...

are the two types of

cerebral cortex The cerebral cortex, also known as the cerebral mantle, is the outer layer of neural tissue of the cerebrum of the brain in humans and other mammals. The cerebral cortex mostly consists of the six-layered neocortex, with just 10% consisting o ...

in the

brain The brain is an organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It consists of nervous tissue and is typically located in the head ( cephalization), usually near organs for special ...

. The allocortex is the much smaller area of cortex taking up just 10 %, the neocortex takes up the remaining 90 %. It is characterized by having just three or four cortical layers, in contrast with the six 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. The specific regions of the brain usually described as belonging to the allocortex are the

olfactory system The olfactory system, or sense of smell, is the sensory system used for smelling (olfaction). Olfaction is one of the special senses, that have directly associated specific organs. Most mammals and reptiles have a main olfactory system and an ac ...

, and the

hippocampus The hippocampus (via Latin from Greek , ' seahorse') is a major component of the brain of humans and other vertebrates. Humans and other mammals have two hippocampi, one in each side of the brain. The hippocampus is part of the limbic system, ...

. Allocortex is termed heterogenetic cortex, because during development it never has the six-layered architecture of homogenetic neocortex. It differs from hetero''typic'' 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 cell A granule is a large particle or grain. It can refer to: * Granule (cell biology), any of several submicroscopic structures, some with explicable origins, others noted only as cell type-specific features of unknown function ** Azurophilic granul ...

Structure

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 The olfactory bulb (Latin: ''bulbus olfactorius'') is a neural structure of the vertebrate forebrain involved in olfaction, the sense of smell. It sends olfactory information to be further processed in the amygdala, the orbitofrontal cortex (O ...

, olfactory tubercle and piriform cortex. Archicortex is a type of cortical tissue that consists of four laminae (layers of neuronal cell bodies). The main areas of archicortex are the

and

dentate gyrus The dentate gyrus (DG) is part of the hippocampal formation in the temporal lobe of the brain, which also includes the hippocampus and the subiculum. The dentate gyrus is part of the hippocampal trisynaptic circuit and is thought to contribute ...

. 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 The entorhinal cortex (EC) is an area of the brain's allocortex, located in the medial temporal lobe, whose functions include being a widespread network hub for memory, navigation, and the perception of time.Integrating time from experience in ...

, 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.

References

* "Allocortex." ''Stedman's Medical Dictionary, 27th ed.'' (2000). * Haines, Duane E. ''Fundamental Neuroscience, 2nd.'' (2002). {{Authority control Cerebral cortex

Structure

See also

References