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Anatomical evidence for segregated processing streams in the cat’s visual cortex Boyd, Jamie D.

Abstract

Studies in primates suggest the existence of at least three separate systems operating in parallel and specialized to process information about: 1) shape; 2) colour; and 3) motion. In visual cortex, these systems are segregated into either the “blobs” staining densely for cytochrome oxidase (CO), or the less densely staining interbiobs. Recent reports of CO blobs in the cat led to this investigation to determine whether CO blobs in this species also act to segregate inputs and outputs. LGN inputs to cat Vi arise from three classes of cells, known as X, Y, and W cells. W cell input was found in different layers of areas 17 and 18 than the X and Y cell input and was localized to CO blobs but not interblobs. The Y cell input from layer C was also found to be confined to the blobs. Area 17 has five major output pathways; to areas 18, 19, 20a, 21a, and the posterior medial lateral suprasylvian area (PMLS). In areas 17 and 18, PMLS-projecting cells were clustered within the CO blobs. Labeling from injections in PMLS was also observed in other cortical areas, and was always clustered, most notably in area 19, where clusters of labeled cells were much wider than in other areas, and often elongated in a direction perpendicular to the 18/19 border. Large injections of tracers into area 19 labeled both blobs and interblobs in areas 17 and 18 while small injections often labeled either only blobs, or only interblobs. Labeling of the callosal pathway, while dense and uniform at the 17/18 border, showed, at the edges of the labeling pattern in areas 17 and 18, regular fluctuations of labeling density that aligned with the CO blobs. Together, these results provide the first demonstration of segregated visual processing streams in a non-primate species. Such an organization may be a general characteristic of mammalian visual cortical organization and not a primate specialization, as was once thought. Knowledge of these pathways in cats, a frequently used system for many developmental and physiological studies, should prove valuable.

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