Periallocortex is one of three subtypes of

allocortex The allocortex (from Latin allo-, meaning other, and cortex, meaning bark or crust), or heterogenetic cortex, is one of the two types of cerebral cortex in the brain, together with the neocortex. In the human brain, the allocortex is the much sm ...

, the other two subtypes being

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

and

archicortex The archicortex, or archipallium, is the phylogenetically second oldest region of the brain's cerebral cortex (the oldest is the paleocortex). In older species, such as fish, the archipallium makes up most of the cerebrum. Amphibians develop an a ...

. The periallocortex is formed at transition areas where any of the other two subtypes of allocortex borders with the

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, ...

(which is also called isocortex). Thus, the periallocortex is also subdivided to two subtypes. One subtype is called

peripaleocortex Peripaleocortex is one of two subtypes of periallocortex, the other being periarchicortex. Peripaleocortex is formed at borders between isocortex (neocortex) and paleocortex (a subtype of allocortex). It shows slow histological transition from th ...

, which is formed at borders between paleocortex and neocortex. Areas considered to belong to peripaleocortex are for example anterior

insular cortex The insular cortex (also insula and insular lobe) is a portion of the cerebral cortex folded deep within the lateral sulcus (the fissure separating the temporal lobe from the parietal lobe, parietal and frontal lobes) within each brain hemisphere ...

. Another subtype of periallocortex is called

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 t ...

. It is formed at borders between archicortex and neocortex. Areas considered to belong to periarchicortex include

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 t ...

perirhinal cortex The perirhinal cortex is a brain cortex, cortical region in the medial temporal lobe that is made up of Brodmann areas Brodmann area 35, 35 and Brodmann area 36, 36. It receives highly processed sensory information from all sensory regions, and i ...

presubiculum Brodmann area 27 is a cytoarchitecturally defined cortical area that is a rostral part of the parahippocampal gyrus. It is commonly regarded as a synonym of presubiculum. The dorsal part of the presubiculum is more commonly known as the postsu ...

parasubiculum In the rodent, the parasubiculum is a retrohippocampal isocortical structure, and a major component of the subicular complex. It receives numerous subcortical and cortical inputs, and sends major projections to the superficial layers of the ento ...

retrosplenial cortex The retrosplenial cortex (RSC) is a cortical area in the brain comprising Brodmann areas 29 and 30. It is secondary association cortex, making connections with numerous other brain regions. The region's name refers to its anatomical location im ...

subcallosal area The subcallosal area (parolfactory area of Broca) is a small triangular field on the medial surface of the hemisphere in front of the subcallosal gyrus, from which it is separated by the posterior parolfactory sulcus; it is continuous below with th ...

and subgenual area. No one allocortex or even periallocortex area borders, contacts or transitions immediately to the so-called true isocortex. Instead, they border and slowly transition to another transitional area from the neocortex side, called

proisocortex Proisocortex or pro-isocortex is one of two subtypes of cortical areas in the areas belonging to the neocortex. The other subtype is termed the true isocortex. Proisocortical areas are transitional areas placed between areas of true isocortex and ...

, which then slowly transitions to the true isocortex. Thus, at borders between isocortex and allocortex there are two transitional areas, one from allocortex side and histologically more resembling allocortex, so it is called periallocortex, and another from isocortex side, histologically more resembling true isocortex, so it is called proisocortex. Those two transitional areas (one from isocortex or neocortex side, called proisocortex, and another from allocortex side, called periallocortex) together form what is called

mesocortex The paralimbic cortex is an area of three-layered cortex that includes the following regions: the piriform cortex, entorhinal cortex, the parahippocampal cortex on the medial surface of the temporal lobe, and the cingulate cortex just above the c ...

References

{{reflist, 3 Cerebral cortex