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, sp ...

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 of ...

in the

brain A brain is an organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It is located in the head, usually close to the sensory organs for senses such as vision. It is the most complex organ in a v ...

. 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 layer 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 of ...

s, in contrast with the six layers of the neocortex. There are three subtypes of allocortex: the

paleocortex In anatomy of animals, the paleocortex, or paleopallium, is a region within the telencephalon in the vertebrate brain. This type of cortical tissue consists of three cortical laminae (layers of neuronal cell bodies). In comparison, the neocortex ...

, the

archicortex The archicortex, or archipallium, is the phylogenetically oldest region of the brain's cerebral cortex. It is often considered contiguous with the olfactory cortex, but its extent varies among species. In older species, such as fish, the archipal ...

, and the

periallocortex Periallocortex is one of three subtypes of allocortex, the other two subtypes being paleocortex and archicortex. The periallocortex is formed at transition areas where any of the other two subtypes of allocortex borders with the neocortex (which ...

—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 ...

, 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, a ...

. 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 Brodmann area 4 refers to the primary motor cortex of the human brain. It is located in the posterior portion of the frontal lobe. Brodmann area 4 is part of the precentral gyrus. The borders of this area are: the precentral sulcus in front (an ...

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 In anatomy of animals, the paleocortex, or paleopallium, is a region within the telencephalon in the vertebrate brain. This type of cortical tissue consists of three cortical laminae (layers of neuronal cell bodies). In comparison, the neocortex ...

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 ( ...

olfactory tubercle The olfactory tubercle (OT), also known as the tuberculum olfactorium, is a multi-sensory processing center that is contained within the olfactory cortex and ventral striatum and plays a role in reward cognition. The OT has also been shown to ...

and

piriform cortex The piriform cortex, or pyriform cortex, is a region in the brain, part of the rhinencephalon situated in the cerebrum. The function of the piriform cortex relates to the sense of smell. Structure The piriform cortex is part of the rhinencepha ...

Archicortex The archicortex, or archipallium, is the phylogenetically oldest region of the brain's cerebral cortex. It is often considered contiguous with the olfactory cortex, but its extent varies among species. In older species, such as fish, the archipal ...

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 t ...

Periallocortex Periallocortex is one of three subtypes of allocortex, the other two subtypes being paleocortex and archicortex. The periallocortex is formed at transition areas where any of the other two subtypes of allocortex borders with the neocortex (which ...

is a transitional form between neocortex and either paleo- or archi-cortex. It thus can be either peripaleocortex (anterior insular cortex) or

periarchicortex Periarchicortex is one of two subtypes of periallocortex, the other being peripaleocortex. It is formed at borders between archicortex (a subtype of allocortex) and isocortex and shows slow histological transition from the four-layered structure ty ...

(

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 the ...

, 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