Orientation column

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

Visualization of neuronal activity in monkey striate cortex.

Abstract: The greatest recent success at describing the functional anatomy of one neocortical area was achieved by Hubel & Wiesel (11) whose work on primary visual (striate) cortex has provided tantalizing information about the topographical organization of two response properties, ocular dominance and orientation selectivity. The first of these is associated with depth perception and refers to the response preference that a neuron shows for one eye or the other. The second property, orientation selectivity, relates to contour detec­ tion and refers to the preference that a neuron shows for edges at particular orientations. Hubel & Wiesel's work has established that both properties remain constant with depth, yet vary systematically with lateral displacement. For ocular dominance this variation arises from the interdigitation of two sets of slabs, each about 0.5 mm wide, and each containing neurons dominated by one eye or the other. For orientational preference this variation occurs con­ tinuously; lateral movements through cortex produce regular and predictable shifts (or rotations) in preferred orientation. At intervals however, that corre­ spond roughly (and curiously) to the widths of ocular dominance slabs, there are sudden jumps in preferred orientation or reversals in the direction of change that disrupt the continuity. Given the obvious importance that lateral arrangements play in the ordering of cortical information, one naturally wonders whether or not there might be a convenient way of studying them-a technique that possibly would allow the direct visualization of responses in cortex to different visual stimuli. The

Lateral inhibitory interactions in areas 17 and 18 of the cat visual cortex.

Abstract: Publisher Summary This chapter discusses the topographical aspects of horizontal connections and the possible functions of gamma-aminobutyric acid–releasing (GABAergic) lateral inhibitory processes in areas 17 and 18 of the feline visual cortex. Orientation selectivity and direction selectivity, as well as length tuning, have been originally described as typical properties of visual cortical cells in response to moving bar-shaped stimuli. The presence of laterally directed axons as morphological substratum for lateral signal processing in the visual cortex was initially shown by degeneration methods in monkeys and cats. Following the demonstration of the clusters of terminals emitted at regular intervals by intracellularly labelled pyramidal cell axons spanning several mm of horizontal distance and the observation of periodic patchy labeling in the visual cortex of monkeys and cats, increasing interest was directed toward horizontal interactions within areas 17 and 18. This interest was focused on the long-range axonal systems of pyramidal cells and predominantly on excitatory functions as shown with cross-correlation analysis of recordings from the pairs of cells with similar orientation specificity. Lateral inhibitory interactions could play a significant role in generating or sharpening specific response properties of visual cortical neurons.

Ocular integration in the human visual cortex.

Abstract: Human striate cortex contains an orderly map of the contralateral visual field, which is distorted to make a disproportionate amount of tissue available for the representation of the macula. Engrafted on the retinotopic map is a system of alternating inputs known as ocular dominance columns. These columns consist of interleaved bands of geniculocortical afferents in layer 4C serving either the right eye or the left eye. They can be revealed in humans with a history of prior visual loss in one eye by processing striate cortex for cytochrome oxidase at autopsy. Because their geniculate input is segregated, cells within ocular dominance columns in layer 4C respond to stimulation of one eye only. These monocular cells converge onto binocular cells in other layers, integrating signals from the two eyes. The columns in humans appear similar to those found in many primate species, including the macaque. In the squirrel monkey, however, the occurrence of ocular dominance columns is highly variable. Some squirrel monkeys lack columns, yet they seem to have no impairment of visual function. In animals with weakly expressed columns, one can detect a cortical pattern of metabolic activity corresponding to retinal blood vessels. It appears because visual deprivation from shadows cast by blood vessels induces remodeling of geniculocortical afferents, in a manner akin to the shrinkage of ocular dominance columns from congenital cataract. Although the function of ocular dominance columns is unknown, their metabolism is altered in strabismus, suggesting a role in visual suppression.

Corticocortical fiber connections of the rabbit visual cortex: a fiber degeneration study.

Abstract: Corticocortical fiber projections of the striate and occipital cortex of the rabbit, as defined by Rose ('31) have been determined by fiber degeneration methods following the production of cortical lesions within each of 24 rabbits. We have assumed that the striate and occipital cortices correspond respectively to the visual cortical areas 1 and 2 (V1 and V2) which have been demarcated electrophysiologically by Thornpson et al. ('50). A study of the ipsilateral fiber projections of the striate and occipital cortex of the rabbit reveals three distinct sets of associational corticocortical connections.(1) Neurons located in layers I-III of all regions of the striate cortex and the occipital cortex send fibers to terminate predominantly in layer V, but also in layers IV and VI, immediately beneath the cells of origin; however, the cells in the supragranular layers have not been found to send fibers to any other region of cerebral cortex. (2) The binocular portions of V1 and V2 appear to be interconnected ipsilaterally since cells in layers IV-VI of the lateral striate cortex have been shown to project to all layers of a restricted, adjacent portion of the medial occipital cortex; and the cells in layers TV-VIof medial occipital cortex send a similar, restricted projection to the adjacent lateral striate cortex. (3) Nerve cells in layers IV-VI of the lateral striate cortex (binocular Vl) send a restricted projection to the lateral portion of the occipital cortex. (4) After all lesions of the striate and/ or occipital cortices, degenerating fibers are seen radiating away from the lesion in layer I; the origin of these degenerating fibers could not be determined. The following observations have been made concerning the origins and terminations of commissural corticorticalfihers. (1) After ablation of most of the visual cortex of one side, commissural fibcrs are secn to terminate in all cortical layers in two narrow bands of visual cortex: one band occupies both sides of the striate-occipital boundary; the second band is found in the lateral portion of occipital cortex. (2) More punctate lesions reveal that commissural fibers arise from layers IV-VI of the lateral striate cortex and medial occipital cortex (binocular portions of V1 and V2 respectively) and end in hornotopic areas of the contralateral cortex.