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Hypercomplex Cell
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A hypercomplex cell (currently called an end-stopped cell) is a type of visual processing neuron in the mammalian cerebral cortex. Initially discovered by David Hubel and Torsten Wiesel in 1965, hypercomplex cells are defined by the property of end-stopping, which is a decrease in firing strength with increasingly larger stimuli. The sensitivity to stimulus length is accompanied by selectivity for the specific orientation, motion, and direction of stimuli. For example, a hypercomplex cell may only respond to a line at 45˚ that travels upward. Elongating the line would result in a proportionately weaker response. Ultimately, hypercomplex cells can provide a means for the brain to visually perceive corners and curves in the environment by identifying the ends of a given stimulus .[1]
Hypercomplex cells were originally characterized as the superordinate class of visual processing cells above complex and simple cells. Whereas complex cells were sensitive to moving stimuli of specific orientations that travel in a specific direction, simple cells only responded to properly oriented linear stimuli. Neither simple nor complex cells were believed to display end-stopping. Likewise, end-stopping was believed to be restricted to higher order visual areas (Brodmann area 18 and Brodmann area 19), but was later discovered to also exist in the primary visual cortex (Brodmann area 17). By 1968, Geoffrey Henry and Bogdan Dreher discovered simple and complex cells with end-stopping properties. Subsequently, hypercomplex cells were no longer recognized as a distinct class but rather a subtype of simple and complex cells. Currently, simple end-stopped and complex end-stopped cells are the terms of choice to describe neurons with end-stopping properties.[1]
![](http://upload.wikimedia.org/wikipedia/commons/thumb/7/70/Brodmann_areas_17_18_19.png/220px-Brodmann_areas_17_18_19.png)