Periarchicortex in the context of "Parasubiculum"

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 areas of periallocortex (which themselves are transitional between "true" allocortex and proisocortex). The histological structure of proisocortex is also transitional between true isocortex and either peripaleocortex or periarchicortex, depending on with which subtype of periallocortex the given proisocortical area borders.

Proisocortex is found in the cingulate cortex (part of the limbic system), in Brodmann's areas 24, 25, 30 and 32, the insula and parahippocampal gyrus.

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 also called isocortex).

Thus, the periallocortex is also subdivided to two subtypes. One subtype is called peripaleocortex, which is formed at borders between paleocortex and neocortex. Areas considered to belong to peripaleocortex are for example anterior insular cortex. Another subtype of periallocortex is called periarchicortex. It is formed at borders between archicortex and neocortex. Areas considered to belong to periarchicortex include entorhinal cortex, perirhinal cortex, presubiculum, parasubiculum, retrosplenial cortex, subcallosal area and subgenual area.

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 the three-layered structure characteristic of paleocortex to the typical six-layered structure characteristic of isocortex. The main peripaleocortex area is anterior insular cortex.

Peripaleocortex does not histologically transit directly to the true isocortex. Instead, at borders between peripaleocortex and isocortex, there are other transitional areas from the isocortex side, called proisocortex. Thus, at borders between paleocortex and isocortex, there are two transitional areas. One transitional area, which is anatomically located closer to the paleocortex side and histologically, too, more resembling "true" paleocortex, is called peripaleocortex area. Another transitional area, which is anatomically located close to the true isocortex side and histologically more resembling it too, is called proisocortex area.