agranular orbitofrontal cortex
Acronym: OFa-p
The term agranular orbitofrontal cortex refers to one of two components of the insulo-orbital agranular cortex of the human ( Ongur-2003 ) and the macaque ( Carmichael-1994 ). While the authors of both studies refer to it as 'agranular_insula', or the orbital part thereof, it is topologically located entirely on the posterolateral surface of the orbital gyri of the frontal lobe. The other component of insulo-orbital agranular cortex is the agranular sector of the insula.
     Defined on the basis of internal structure, it is identified by multiple stains. Caudally it is continuous with the agranular sector of the insula. It is bounded rostrally by area 13 and area 47/12. It is one of nine subdivisions of the orbitomedial prefrontal cortex in the human; the others besides those mentioned are area 10, area 11, area 24, area 25, area 32ac, and area 32pl. In the human it has four (perhaps five, see below) subdivisions: area Iam, area Iapm, area Iai, and area Ial ( Ongur-2003 ).
     The macaque has corresponding areas ( Carmichael-1994 ): area Iam (macaque), area Iapm ( macaque), area Iai (macaque), and area Ial (macaque) an area Iapl (macaque), which may have an equivalent in the human located beyond the portion of cortex evaluated by authors of the human study ( Ongur-2003 ).
     In the macaque, the agranular orbitofrontal cortex is one of six components of the orbitomedial prefrontal cortex (macaque). In that context it consists of two subdivisions: the medial agranular insular region and the lateral agranular insular region ( Carmichael-1994 ). It is considered to be the periallocortex of two paleocortical structures, the claustrum and the piriform area ( Mesulam-1982; Carmichael-1994; Zilles-2004 ).
     While it has no topological equivalent in the smooth cortex of the rat ( Swanson-2004 ) and mouse ( Dong-2004 ), its parent structure, insulo-orbital agranular cortex, is architecturally equivalent to the rodent's agranular insular cortex. That is located rostrally on the ventrolateral surface of the cerebral cortex, dorsal to the piriform area and ventral to the gustatory cortex and visceral cortex.
     Note that the insulo-orbital agranular cortex is different from, and does not overlap, the agranular insular cortex (Roberts), which is based on a different segmentation of the insula.

Also known as: orbito-insular cortexNeuroNames ID : 3501

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