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The superior colliculus, (Latin, ''upper hill'') is a paired structure of the mammalian midbrain. In other vertebrates this is known as the optic tectum or simply tectum, and the adjective ''tectal'' may also be used. The superior colliculus forms a major component of the midbrain. The tectum is a layered structure, with a number of layers that varies by species. The superficial layers are sensory-related, and receive input from the eyes as well as other sensory systems.〔Wallace et al., 1998〕 The deep layers are motor-related, capable of activating eye movements as well as other responses. There are also intermediate layers, with multi-sensory cells and motor properties. The general function of the tectal system is to direct behavioral responses toward specific points in egocentric ("body-centered") space. Each layer of the tectum contains a topographic map of the surrounding world in retinotopic coordinates, and activation of neurons at a particular point in the map evokes a response directed toward the corresponding point in space. In primates, the superior colliculus has been studied mainly with respect to its role in directing eye movements. Visual input from the retina, or "command" input from the cerebral cortex, create a "bump" of activity in the tectal map, which, if strong enough, induces a saccadic eye movement. Even in primates, however, the tectum is also involved in generating spatially directed head turns, arm-reaching movements,〔Lunenburger et al., 2001〕 and shifts in attention that do not involve any overt movements.〔 In other species, the tectum is involved in a wide range of responses, including whole-body turns in walking rats, swimming fishes, or flying birds; tongue-strikes toward prey in frogs; fang-strikes in snakes; etc. In some vertebrates, including fish and birds, the tectum is one of the largest components of the brain. In mammals, and especially primates, the massive expansion of the cerebral cortex reduces the tectum ("superior colliculus") to a much smaller fraction of the whole brain. It remains nonetheless important in terms of function as the primary integrating center for eye movements. ''Note on terminology'': This article follows terminology established in the literature for the analogous structure in mammals/non-mammals (see above), using the term "superior colliculus" when discussing mammals and "optic tectum" when discussing either specific non-mammalian species or vertebrates in general. ==Structure== The two superior colliculi sit below the thalamus and surround the pineal gland in the vertebrate midbrain. It comprises the dorsal aspect of the midbrain, posterior to the periaqueductal gray and immediately superior to the inferior colliculus. The inferior and superior colliculi are known collectively as the corpora quadrigemina (Latin, ''quadruplet bodies''). The brachium of superior colliculus (or superior brachium) extends laterally from the superior colliculus, and, passing between the pulvinar and medial geniculate body, is partly continued into an eminence called the lateral geniculate body, and partly into the optic tract. 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「Superior colliculus」の詳細全文を読む スポンサード リンク
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