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The allocortex (also known as heterogenetic cortex) is one of the two types of cerebral cortex, the other being the neocortex. It is characterized by having just three or four cell layers, in contrast with the six layers of the neocortex, and takes up a much smaller area than the neocortex. There are three subtypes of allocortex: the paleocortex, the archicortex, and the periallocortex – a transitional zone between the neocortex and the allocortex.〔http://braininfo.rprc.washington.edu/centraldirectory.aspx?ID=2315〕 The specific regions of the brain usually described as belonging to the allocortex are the olfactory system, and the hippocampus. Allocortex is termed heterogenetic cortex, because during development it never has the six-layered architecture of homogenetic neocortex. It differs from heterotypic 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 cells.〔Crosby EC; Humphrey T; Lauer EW (1962)Correlative Anatomy of the Nervous System. New York: MacMillan〕 ==Structure== The allocortex has just 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 to five cortical laminae (layers of neuronal cell bodies). In comparison, the neocortex has six layers and the archicortex has three or four layers.〔Purves et al: Neuroscience 3rd Edition, 2004, page 617〕 Archicortex is a type of cortical tissue that consists of three laminae (layers of neuronal cell bodies). It has fewer layers than both neocortex, which has six, and paleocortex, which has either four or five. 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, paleocortex is thought to be an intermediate between neocortex and archicortex in both aspects, and archicortex is thought to be the oldest and most basic type of cortical tissue.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「allocortex」の詳細全文を読む スポンサード リンク
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