Orientation column

About: Orientation column is a research topic. Over the lifetime, 1142 publications have been published within this topic receiving 130169 citations.

Desegregation: Bussing of Signals Through the Retinal Network

Abstract: One of the information processing principles that has been repeatedly discovered in the nervous system is the segregation of signals into separate but parallel pathways. In the visual system, for example, separationist groups such as ocular dominance and orientation columns have been uncovered in the visual cortex (8). This reactionary processing is also prominent in the retina where there is an apparent separation of rod-cone, ON-OFF, and transient-sustained signals (7,9,11, 23). These various modalities decompose images from the outside world into informational components that can be processed by the nervous system. This model of sensory processing proposes that images from the outside world are handled by a multiplicity of parallel pathways, each relaying information about a particular characteristic of the external image, such as its color, orientation, or direction of motion. This theory has found strong support in the discovery of neurons that are preferentially stimulated by one of these trigger features (2,12). Although this appears to be an important mechanism in sensory systems, recent studies in amphibian retina suggest that the segregation of signals is not so absolute, and that in fact there may be a mixing of signals which at face value seems to contradict the principles of decomposition and segregation that enables animals to interpretation the visual world.

Chapter 8 – Do Lateral Intrinsic and Callosal Axons Have Comparable Actions in Early Visual Areas?

Abstract: Anatomy and function of long-range intrinsic and callosal axons in primary visual cortex are reviewed. In cats, both arborize in a patchy manner, in an orderly relationship to the visuotopic map and visual stimulus features. Patches tend to link neurons with similar contour and direction preference aligned along a collinear visual field axis. Direct investigation of callosal action on visual responses reveals a multiplicative shift without changing neuronal selectivity. Both gain and bias toward excitation or inhibition depend on global stimulus attributes. Interactions are more pronounced for neurons processing similar, in particular cardinal, visual features. As feature selectivity emerges already in ongoing neuronal activity, it is hypothesized that perceptual grouping is anticipated via the feature bias in patchy connections. By comparing data from lateral and feedback circuits, we conclude that visual callosal connections are more similar to intrinsic connections and can be interpreted as extending this circuit across the hemispheres.

Effect of division of cortico — Subcortical connections on spontaneous unit activity in the lateral geniculate body and visual cortex

Abstract: In acute experiments on cats the cortical projection connections of one hemisphere were divided, and the principal characteristics of spontaneous unit activity were studied in the lateral geniculate bodies (LGB) and visual cortex (area 17). After the operation the same types of spontaneous activity were found in these structures as in the intact structures. However, the number of spontaneously active cells in the structures on the side of the operation was considerably reduced. In the isolated visual cortex there was a redistribution of the relative percentage of neurons with spontaneous activity in the various layers: these cells were most numerous in layers IV–V, whereas in the normal cortex they are more numerous in layers III–IV. The mean firing rate of all types of cells was reduced in the isolated cortex. In LGB on the side of the operation a relative decrease in the number of cells with a high firing rate was observed.