The term third visual complex refers to the region of cortex located immediately in front of V2, which includes the region named visual area V3. The "complex" nomenclature is justified by the fact that some controversy still exists regarding the exact extent of area V3, with some researchers proposing that the cortex located in front of V2 may include two or three functional subdivisions.

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Subdivisions of V3

Some have proposed the existence of a "dorsal V3" distinct from the "ventral V3" (or ventral posterior area, VP) located in the lower part of the brain.

Dorsal and ventral V3 have distinct connections with other parts of the brain, appear different in sections stained with a variety of methods, and contain neurons that respond to different combinations of visual stimulus (for example, colour-selective neurons are more common in the ventral V3). Additional subdivisions, including V3A and V3B have also been reported.

Location

Dorsal V3 is normally considered to be part of the dorsal stream, receiving inputs from V2 and from the primary visual area and projecting to the posterior parietal cortex. It may be anatomically located in Brodmann area 19.

Functions

Braddick using fMRI has suggested that area V3/V3A may play a role in the processing of global motion.
Others consider dorsal V3 as part of a larger area, the dorsomedial area (DM), which contains a representation of the entire visual field.
Neurons in area DM respond to coherent motion of large patterns covering extensive portions of the visual field.

Ventral V3 (VP), has much weaker connections from the primary visual area, and stronger connections with the inferior temporal cortex. While earlier studies proposed that VP contained a representation of only the upper part of the visual field (above the point of fixation), more recent work indicates that this area is more extensive than previously appreciated, and like other visual areas it may contain a complete visual representation. The revised, more extensive VP is referred to as the ventrolateral posterior area (VLP)