The Superior Colliculus

The superior colliculus is located on the dorsal surface of the brain stem. Unconscious visual input goes directly from the retina to the colliculus, and therefore implicates this neural tissue in navigational processing (related to the peripheral "where" retina).

Output from the superior colliculus goes to motor centers responsible for orienting behaviors. Orienting behaviors are immediate, rapid organism responses (reflexes), usually to movement. A dark spot moving at a given speed across a frog retina causes the frog to flick its tongue outward to snag the fly. A large shadow across the frog retina causes the amphibian to jump into the water and dive for cover. These are brain stem level, automatic behaviors caused by reflex patterns governed by the superior colliculus.

In higher animals the cerebral centers analyze input in association with (or before) the superior colliculus. In primates the colliculus controls the automatic saccades that put the retina in position to analyze sudden movements across the retina.

In surgical cases where the corpus callosum has been severed, the lower brain commissures often are not cut. Important, lower level (subconscious) visual processing systems, primarily the superior colliculus and hippocampal areas have commissures that connect the two sides of the brain. When these are not severed, there remains significant hemisphere crossover. This helps explain why patients still have good mobility skills after cutting the corpus callosum. It also helps explain why cortically blinded individuals have "blind sight", why they are able to avoid obstacles and move about even though they have no conscious awareness of this "sight."


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