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The hippocampus (named after its resemblance to the seahorse, from the Greek ἱππόκαμπος, "seahorse" from ἵππος ''hippos'', "horse" and κάμπος ''kampos'', "sea monster") is a major component of the brains of humans and other vertebrates. Humans and other mammals have two hippocampi, one in each side of the brain. It belongs to the limbic system and plays important roles in the consolidation of information from short-term memory to long-term memory and spatial navigation. The hippocampus is located under the cerebral cortex;〔Wright, Anthony. (Chapter 5: Limbic System: Hippocampus ). Department of Neurobiology and Anatomy, The UT Medical School at Houston〕 and in primates it is located in the medial temporal lobe, underneath the cortical surface. It contains two main interlocking parts: Ammon's horn〔Pearce, 2001〕 and the dentate gyrus. In Alzheimer's disease, the hippocampus is one of the first regions of the brain to suffer damage; memory loss and disorientation are included among the early symptoms. Damage to the hippocampus can also result from oxygen starvation (hypoxia), encephalitis, or medial temporal lobe epilepsy. People with extensive, bilateral hippocampal damage may experience anterograde amnesia—the inability to form and retain new memories. In rodents, the hippocampus has been studied extensively as part of a brain system responsible for spatial memory and navigation. Many neurons in the rat and mouse hippocampus respond as place cells: that is, they fire bursts of action potentials when the animal passes through a specific part of its environment. Hippocampal place cells interact extensively with head direction cells, whose activity acts as an inertial compass, and conjecturally with grid cells in the neighboring entorhinal cortex. Since different neuronal cell types are neatly organized into layers in the hippocampus, it has frequently been used as a model system for studying neurophysiology. The form of neural plasticity known as long-term potentiation (LTP) was first discovered to occur in the hippocampus and has often been studied in this structure. LTP is widely believed to be one of the main neural mechanisms by which memory is stored in the brain. == Name == The earliest description of the ridge running along the floor of the temporal horn of the lateral ventricle comes from the Venetian anatomist Julius Caesar Aranzi (1587), who likened it first to a silkworm and then to a seahorse (Latin: ''hippocampus'' from Greek: ἵππος, "horse" and κάμπος, "sea monster"). The German anatomist Duvernoy (1729), the first to illustrate the structure, also wavered between "seahorse" and "silkworm." "Ram's horn" was proposed by the Danish anatomist Jacob Winsløw in 1732; and a decade later his fellow Parisian, the surgeon de Garengeot, used "cornu Ammonis" – horn of (the ancient Egyptian god) Amun.〔Duvernoy, 2005〕 Another mythological reference appeared with the term ''pes hippocampi'', which may date back to Diemerbroeck in 1672, introducing a comparison with the shape of the folded back forelimbs and webbed feet of the Classical hippocampus (Greek: ἱππόκαμπος), a sea monster with a horse's forequarters and a fish's tail. The hippocampus was then described as ''pes hippocampi major'', with an adjacent bulge in the occipital horn, the calcar avis, being named ''pes hippocampi minor''.〔 The renaming of the hippocampus as hippocampus major, and the calcar avis as hippocampus minor, has been attributed to Félix Vicq-d'Azyr systematising nomenclature of parts of the brain in 1786. Mayer mistakenly used the term hippopotamus in 1779, and was followed by some other authors until Karl Friedrich Burdach resolved this error in 1829. In 1861 the hippocampus minor became the centre of a dispute over human evolution between Thomas Henry Huxley and Richard Owen, satirised as the Great Hippocampus Question. The term hippocampus minor fell from use in anatomy textbooks, and was officially removed in the Nomina Anatomica of 1895.〔Gross, 1993〕 Today, the structure is called the hippocampus rather than hippocampus major, with ''pes hippocampi'' often being regarded as synonymous with De Garengeot's "cornu Ammonis",〔 a term that survives in the names of the four main histological divisions of the hippocampus: CA1, CA2, CA3, and CA4.〔Wechsler, 2004〕 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「Hippocampus」の詳細全文を読む スポンサード リンク
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