Superior colliculus

Superior colliculus
Diagram of the superior colliculus (L) of the human midbrain (shown in red) and surrounding regions. The superior colliculus is surrounded by a red ring and transparent red circle to indicate its location.
Section through midbrain at the level of the superior colliculus showing path of oculomotor nerve
Details
Part of	Tectum
Identifiers
Latin	colliculus superior
MeSH	D013477
NeuroNames	473
NeuroLex ID	birnlex_1040
TA98	A14.1.06.015
TA2	5912
TH	H3.11.03.3.01002
TE	colliculus_by_E5.14.3.3.1.4.4 E5.14.3.3.1.4.4
FMA	62403
Anatomical terms of neuroanatomy [edit on Wikidata]

In neuroanatomy, the superior colliculus (from Latin 'upper hill') is a structure lying on the roof of the mammalian midbrain.^[1] In non-mammalian vertebrates, the homologous structure is known as the optic tectum or optic lobe.^[1][2][3] The adjective form tectal is commonly used for both structures.

In mammals, the superior colliculus forms a major component of the midbrain. It is a paired structure and together with the paired inferior colliculi forms the corpora quadrigemina. The superior colliculus is a layered structure, with a pattern that is similar to all mammals.^[4] The layers can be grouped into the superficial layers (stratum opticum and above) and the deeper remaining layers. Neurons in the superficial layers receive direct input from the retina and respond almost exclusively to visual stimuli. Many neurons in the deeper layers also respond to other modalities, and some respond to stimuli in multiple modalities.^[5] The deeper layers also contain a population of motor-related neurons, capable of activating eye movements as well as other responses.^[6] In other vertebrates the number of layers in the homologous optic tectum varies.^[4]

The general function of the tectal system is to direct behavioral responses toward specific points in body-centered space. Each layer 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 superior colliculus is also involved in generating spatially directed head turns, arm-reaching movements,^[7] and shifts in attention that do not involve any overt movements.^[8] In other species, the superior colliculus is involved in a wide range of responses, including whole-body turns in walking rats. In mammals, and especially primates, the massive expansion of the cerebral cortex reduces the 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.

In non-mammalian species the optic tectum is involved in many responses including swimming in fish, flying in birds, tongue-strikes toward prey in frogs, and fang-strikes in snakes. In some species, including fish and birds, the optic tectum, also known as the optic lobe, is one of the largest components of the brain.

Note on terminology: This article follows terminology established in the literature, using the term "superior colliculus" when discussing mammals and "optic tectum" when discussing either specific non-mammalian species or vertebrates in general.