Showing papers on "Orientation column published in 1988"

Experimentally induced visual projections into auditory thalamus and cortex

Abstract: Retinal cells have been induced to project into the medial geniculate nucleus, the principal auditory thalamic nucleus, in newborn ferrets by reduction of targets of retinal axons in one hemisphere and creation of alternative terminal space for these fibers in the auditory thalamus. Many cells in the medial geniculate nucleus are then visually driven, have large receptive fields, and receive input from retinal ganglion cells with small somata and slow conduction velocities. Visual cells with long conduction latencies and large contralateral receptive fields can also be recorded in primary auditory cortex. Some visual cells in auditory cortex are direction selective or have oriented receptive fields that resemble those of complex cells in primary visual cortex. Thus, functional visual projections can be routed into nonvisual structures in higher mammals, suggesting that the modality of a sensory thalamic nucleus or cortical area may be specified by its inputs during development.

A theory for the use of visual orientation information which exploits the columnar structure of striate cortex

Abstract: A neural model is constructed based on the structure of a visual orientation hypercolumn in mammalian striate cortex. It is then assumed that the perceived orientation of visual contours is determined by the pattern of neuronal activity across orientation columns. Using statistical estimation theory, limits on the precision of orientation estimation and discrimination are calculated. These limits are functions of single unit response properties such as orientation tuning width, response amplitude and response variability, as well as the degree of organization in the neural network. It is shown that a network of modest size, consisting of broadly orientation selective units, can reliably discriminate orientation with a precision equivalent to human performance. Of the various network parameters, the discrimination threshold depends most critically on the number of cells in the hypercolumn. The form of the dependence on cell number correctly predicts the results of psychophysical studies of orientation discrimination. The model system's performance is also consistent with psychophysical data in two situations in which human performance is not optimal. First, interference with orientation discrimination occurs when multiple stimuli activate cells in the same hypercolumn. Second, systematic errors in the estimation of orientation can occur when a stimulus is composed of intersecting lines. The results demonstrate that it is possible to relate neural activity to visual performance by an examination of the pattern of activity across orientation columns. This provides support for the hypothesis that perceived orientation is determined by the distributed pattern of neural activity. The results also encourage the view of neural activity. The results also are determined by the responses of many neurons rather than the sensitivity of individual cells.

Functional anatomy of macaque striate cortex. IV. Contrast and magno- parvo streams

Abstract: Macaque monkeys were shown achromatic gratings of various contrasts during 14C-2-deoxy-d-glucose (DG) infusion in order to measure the contrast sensitivity of different subdivisions of primary visual cortex. DG uptake is essentially saturated at stimulus contrasts of 50% and above, although the saturation contrast varies with layer and with different criteria. Following visual stimulation with gratings of 8% contrast, stimulus-driven uptake was relatively high in striate layer 4Ca (which receives primary input from the magnocellular LGN layers), but was absent in layer 4Cb (which receives primary input from the parvocellular layers). In this same (magnocellular-specific) stimulation condition, striate layers 4B, 4Ca, and 6 showed strong stimulus-induced DG uptake, and layers 2, 3, 4A, and 5 showed only light or negligible uptake. By comparison to other cases that were shown stimuli of systematically higher contrast, and to a wide variety of DG cases shown very different stimuli, it is evident that information derived from the magnocellular and parvocellular layers in the LGN remains partially, or largely, segregated in its passage through striate cortex, and projects in a still somewhat segregated fashion to different extrastriate areas. The sum of all available evidence suggests that the magnocellular information projects strongly through striate layers 4Ca, 4B, and 6, with moderate input into the blobs in layers 2 + 3, and to blob-aligned portions of layer 4A. Parvocellular-dominated regions of striate cortex include both the blob and interblob portions of layers 2 + 3, 4A, 4Cb, and 5. Because the major striate input to V2 arrives from striate layers 2 + 3, and because the major striate input to MT originates in layer 4B and 6, it appears that area V2 receives information derived largely from the parvocellular LGN layers, and that area MT receives information derived mainly from the magnocellular layers.

Organization of primary visual cortex (area 17) in the ferret.

Abstract: Anatomical and electrophysiological mapping techniques were used to determine topographic organization and arrangement of ocular dominance columns in the primary visual cortex of ferrets. From its border with area 18 on the posterior lateral gyrus, area 17 extends around the caudal pole of the hemisphere and over the splenial gyrus to the caudal bank of the splenial sulcus. The visuotopic map is oriented with the isoazimuth lines approximately parallel to the long axis of the posterior lateral gyrus and the isoelevation lines approximately perpendicular to the isoazimuths. Central azimuths are represented on the posterior lateral gyrus and peripheral azimuths are represented on the splenial gyrus; the inferior visual field maps medially and the superior visual field maps laterally. As in other species, the representation of the central visual field is expanded. The ferret has a considerable degree of binocular vision. Receptive fields driven through the ipsilateral eye extended more than 20 degrees into the contralateral visual field. Within the region of area 17 corresponding to the binocular portion of the visual field, tritiated proline injected into one eye transneuronally labelled an ipsilateral projection as a series of patchy bands roughly complementary to gaps in the labelled contralateral projection. Physiological ocular dominance columns were evident as well in that neurons and groups of neurons recorded in this region showed clustered ocular dominance preferences. Most single neurons studied were binocularly driven.

Functional anatomy of macaque striate cortex. I. Ocular dominance, binocular interactions, and baseline conditions

Abstract: A series of experiments was carried out using 14C-2-deoxy-d-glucose (DG) in order to examine the functional architecture of macaque striate (primary visual) cortex. This paper describes the results of experiments on uptake during various baseline (or reference) conditions of visual stimulation (described below), and on differences in the functional architecture following monocular versus binocular viewing conditions. In binocular “baseline” experiments, monkeys were stimulated either (1) in the dark, (2) with a diffuse gray screen, or (3) with a very general visual stimulus composed of gratings of varied orientation and spatial frequency. In all of these conditions, DG uptake was found to be topographically uniform within all layers of parafoveal striate cortex. In monocular experiments that were otherwise similar, uptake was topographically uniform within the full extent of the eye dominance strip, in all layers. Certain other visual stimuli produce high uptake in the blobs, and still another set of visual stimuli (including high-spatial-frequency gratings) produce highest uptake between the blobs at parafoveal eccentricities, even in an unanesthetized, unparalyzed monkey. Eye movements per se had no obvious effect on striate DG uptake. Endogenous uptake in the blobs (relative to that in the interblobs) appears higher in the squirrel monkey than in the macaque. The pattern of DG uptake produced by binocular viewing was found to deviate in a number of ways from that expected by linearly summing the component monocular DG patterns. One of the most interesting deviations was an enhancement of the representation of visual field borders between stimuli differing from each other in texture, orientation, direction, etc. This “border enhancement” was confined to striate layers 1–3 (not appearing in any of the striate input layers), and it only appeared following binocular, but not monocular, viewing conditions. The border enhancement may be related to a suppression of DG uptake that occurs during binocular viewing conditions in layers 2 + 3 (and perhaps layers 1 and 4B), but not in layers 4Ca, 4Cb, 5 or 6. Another major class of binocular interaction was a spread of neural activity into the “unstimulated” ocular dominance strips following monocular stimulation. Such an effect was prominent in striate layer 4Ca, but it did not occur in layer 4Cb. This “binocular” spread of DG uptake into the inappropriate eye dominance strip in 4Ca may be related to the appearance of orientation tuning and orientation columns in that layer. No DG effects were seen that depended on the absolute disparity of visual stimuli in macaque striate cortex.

The primary visual cortex in the mouse: receptive field properties and functional organization.

Abstract: Receptive field (RF) characteristics of cells in primary visual cortex of the mouse (C57B16 strain) were studied by single unit recording. We have studied the functional organization of area 17 along both the radial and tangential dimensions of the cortex. Eighty seven percent of the visual neurons could be classified according to their responses to oriented stimuli and to moving stimuli. Cells which preferred a flashed or moving bar of a particular orientation and responded less well to bars of other orientations or to spots, were classified as orientation selective (simple RF 23%, complex RF 18%). The majority of them were, moreover, unidirectional (24%). All orientations were roughly equally represented. Cells with oriented RFs were recorded mostly in the upper part of cortical layers II-III, where they appeared to be clustered according to their preferred orientation. Neurons that responded equally well to spots and bars of all orientations (46%) were classified as "non-oriented"; among these neurons there were several subcategories. Cells which responded equally well to spots and bars but preferred stimuli moving along one or both directions of a particular axis were classified as non oriented asymmetric cells (unidirectional 14%, bidirectional 4%). They were recorded mainly in supra- and infra-granular layers. Cells unaffected by stimulus shape and orientation which responded equally well to all directions of movement were classified as symmetric units. They had receptive field classified as ON (11%), OFF (1%), ON/OFF (11%), or were unresponsive to stationary stimuli (5%). These cells were mostly found in layer IV, in which they constituted the majority of recorded cells. There was no apparent correlation between the functional type and size of RFs. However, the greatest proportion of small RFs was found in layer IV. In the binocular segment of the mouse striate cortex, the influence of the contralateral eye predominated. Ninety five percent of cells in this segment were driven through the contralateral eye. However, 70% of cells were binocularly activated, showing that considerable binocular integration occurred in this cortical segment. Ocular dominance varied less along the radial than along the tangential dimension of the cortex.

Inhibition contributes to orientation selectivity in visual cortex of cat.

Abstract: Neurons in the visual cortex are selectively responsive to light or dark bars presented at particular orientations1. On the basis of physiological data, this orientation selectivity is hypothesized as being due at least partially to intracortical inhibitory mechanisms2–6. But this hypothesis has been challenged by intracellular recordings indicating that excitatory inputs themselves are orientation-selective, so inhibition may not contribute to the observed selectivity7. Also, there is controversy about the presence of intracortical horizontal connections mediating inhibition for selectivity8–11 and about the theoretical validity of such inhibitory connections12–14. Using cross-correlation analysis of the activities of two neurons recorded simultaneously, we find that inhibitory interactions exist between cells with somewhat different, but not orthogonal, orientation preferences. This suggests that intracortical horizontal inhibition operates between 'orientation columns' to sharpen the orientation tuning of cortical neurons.

Two-dimensional spatial structure of receptive fields in monkey striate cortex

Abstract: Measurements of the spatial contrast sensitivity function and orientation selectivity of visual neurons in the foveal striate cortex (V1) of primates were interpreted within the context of a model of the two-dimensional spatial structure of their receptive fields Estimates of the spatial dimensions of the receptive fields along the axis of preferred orientation were derived from the application of the model and were compared with estimates of the smallest spatial subunit in the dimension orthogonal to the preferred orientation Some measure of agreement was found with corresponding estimates of parameters for psychophysical channels in human foveal vision

Visual cortex of the dolphin: an image analysis study.

Abstract: On cytoarchitectonic grounds we have identified two distinct types of cortical formations composing the lateral gyrus (visual cortex) of the dolphin and have termed these heterolaminar cortex and homolaminar cortex. The heterolaminar cortex occupies the medial and lateral banks of the entolateral sulcus whereas the homolaminar cortex occupies the remainder of the lateral gyrus both lateral and medial to the entolateral sulcus. Each of these cortices exhibits special cytoarchitectonic features, a major difference being that heterolaminar cortex contains an incipient layer IV whereas layer IV is clearly absent in homolaminar cortex. Quantitative imaging procedures reveal that there is greater laminar differentiation in heterolaminar than in homolaminar cortex. Golgi analysis of neuronal forms and dendritic architecture confirms this distinction between the two types of cortex composing the lateral gyrus. Computer-assisted morphometric methods have been applied to both types of cortex and indicate by a variety of parameters several quantitative differences in the cellular numbers, types, and organization in each type of cortex. Both types of cortex, homolaminar and heterolaminar, exhibit a markedly higher cellular density in the posterior sector of the lateral gyrus than in the anterior sector. We have also for the first time been able to identify a columnar type of organization of the cetacean visual cortex and have described two types of cytoarchitectonic columns, major and minor, in each of these types of cortex. Comparisons in organization of these basic columnar units between the bat, representing a prototypic brain, and the dolphin reveal many similarities but also major quantitative differences in type of organization between the visual cortices in these species. Marked differences are also seen between the cytoarchitectonic columnar organization of the visual cortices in the dolphin and columnar organization of striate cortex in the human brain, the number of columns per unit of cortex in the human being almost twice that seen in the dolphin brain. Some phylogenetic implications of these findings are discussed in relation to the so-called "initial" type of cortical organization reconstructed largely by retrospective inference.

Small lateral suprasylvian cortex lesions produce visual neglect and decreased visual activity in the superior colliculus.

Abstract: Previous experiments in cats have shown that complete contralateral visual neglect is produced by removing all known visual cortex on one side of the brain, which can then be reversed by damaging the opposite superior colliculus. Presumably, descending facilitatory influences from the visual cortex to the ipsilateral superior colliculus are counterbalanced by intercollicular inhibition (Sprague: Science 153:1544-1546, '66). However, not all of visual cortex or all of the superior colliculus needs to be involved in this circuit. It is the deep rather than the superficial laminae of the superior colliculus that are primarily involved in visual attentive and orientation behaviors, and these laminae are largely independent of primary visual cortex. However, they do depend on corticotectal influences from a comparatively small extraprimary visual area of the posterior region of the lateral suprasylvian cortex (PSSC-Ogasawara et al: J. Neurophysiol. 52:1226-1245, '84). The present experiments demonstrate that lesions only a few millimeters in diameter in this corticotectal zone of the PSSC can produce profound visual neglect. While damage to this area has little, if any, effect on superficial laminae visual activity, it produces a dramatic decrease in the visual activity of the deep laminae. These cats with PSSC lesions fail to orient to a visual stimulus that is introduced suddenly into the contralateral visual field, yet they respond on nearly 100% of the trials to this same stimulus when it is presented in the ipsilateral visual field. The lesion-induced visual neglect produced by PSSC lesions is long-lasting but can be abruptly ameliorated by a midbrain lesion that primarily involves, or undercuts, the deep laminae of the contralateral superior colliculus. Thus, 1) visual neglect can be produced by depriving the deep laminae of the superior colliculus of visual inputs from the cortex, even when the principal visual cortical regions (17, 18, and 19) and their target structures are intact, and 2) visually guided behavior can be restored by eliminating afferents originating in, or passing through, the deep laminae of the contralateral superior colliculus.

Topographic relations between ocular dominance and orientation columns in the cat striate cortex.

Abstract: In the visual cortex of four adult cats ocular dominance and orientation columns were visualized with (3H)proline and (14C)deoxyglucose autoradiography. The two columnar systems were reconstructed from serial horizontal sections or from flat-mount preparations and graphically superimposed. They share a number of characteristic features: In both systems the columns have a tendency to form regularly spaced parallel bands whose main trajectory is perpendicular to the border between areas 17 and 18. These bands frequently bifurcate or terminate in blind endings. The resulting irregularities are much more pronounced in the ocular dominance than in the orientation system. The periodicity of the columnar patterns was assessed along trajectories perpendicular to the main orientation of the bands and differed in the two columnar systems. The spacing of the ocular dominance stripes was significantly narrower than the spacing of orientation bands. The mean periodicity of a particular columnar system was virtually identical in the two hemispheres of the same animal but it differed substantially in different animals. However, the spacing of orientation columns covaried with that of the ocular dominance columns, the ratios of the mean spacings of the two columnar systems being similar in the four cats. The superposition of the two columnar systems revealed no obvious topographic relation between any of the organizational details such as the location of bifurcations, blind endings and intersections. We suggest the following conclusions: 1. The developmental processes generating the two columnar systems seem to obey the same algorithms but they act independently of each other. 2. The space constants of the two systems are rigorously specified and appear to depend on a common variable. 3. The main orientation of the bands in both columnar systems is related to a) the representation of the vertical meridian, b) the anisotropy of the cortical magnification factor, and c) the tangential spread of intracortical connections.

Metabolic activity in striate and extrastriate cortex in the hooded rat: contralateral and ipsilateral eye input.

Abstract: The extent of changes in glucose metabolism resulting from ipsilateral and contralateral eye activity in the posterior cortex of the hooded rat was demonstrated by means of the C-14 2-deoxyglucose autoradiographic technique. By stimulating one eye with square wave gratings and eliminating efferent activation from the other by means of enucleation or intraocular TTX injection, differences between ipsilaterally and contralaterally based visual activity in the two hemispheres were maximized. Carbon-14 levels in layer IV of autoradiographs of coronal sections were measured and combined across sections to form right and left matrices of posterior cortex metabolic activity. A difference matrix, formed by subtracting the metabolic activity matrix of cortex contralateral to the stimulated eye from the ipsilateral "depressed" matrix, emphasized those parts of the visual cortex that received monocular visual input. The demarcation of striate cortex by means of cholinesterase stain and the examination of autoradiographs from sections cut tangential to the cortical surface aided in the interpretation of the difference matrices. In striate cortex, differences were maximal in the medial monocular portion, and the lateral or binocular portion was shown to be divided metabolically into a far lateral contralaterally dominant strip along the cortical representation of the vertical meridian, and a more medial region of patches of more or less contralaterally dominant binocular input. Lateral peristriate differences were less than those of striate cortex, and regions of greater and lesser monocular input could be distinguished. We did not detect differences between the two hemispheres in either anterior or medial peristriate areas, thus indicating either completely binocular input (which seems unlikely given the retinotopic organization of these regions), or a greater dependence than in the lateral peristriate on inputs that were not affected by the visual manipulations.

The ipsilateral field representation in the striate cortex of the opossum.

Abstract: Reference axes for the visuotopic study of the opossum's striate cortex were estimated from corresponding binocular response fields using multi-unit recording. These central binocular axes (CBA) were derived from experimental data based on the concept that corresponding receptive fields for each eye should be mostly in register under natural conditions. Vertical reference meridians, orthogonal to these axes, define a contralateral and an ipsilateral field for each eye with respect to the recording site. An ipsilateral field representation was observed for both eyes in the striate cortex at the transition zone with peristriate. Maximal values for the center and border of ipsilateral receptive fields were, respectively, 8 and 20 degrees for the contralateral eye and 6 and 14 degrees for the ipsilateral eye. An equivalent ipsilateral field representation was found in animals that had the anterior commissure cut prior to the recording session. This suggests that the ipsilateral field of both eyes may be represented in the striate cortex via the ipsilateral optic tract. Additionally, it was observed that the region of higher ganglion cell density in the retina shows a flattened distribution and that the CBA intersects the retina at the temporal aspect of this region.

Interconnections of the visual cortex with the frontal cortex in the rat.

Abstract: Horseradish peroxidase conjugated to wheat germ agglutinin (WGA-HRP) and autoradiography of tritiated leucine were used to trace the cortical origins and terminations of the connections between the visual and frontal cortices in the rat. Ipsilateral reciprocal connections between each subdivision of the visual cortex (areas 17, 18a and 18b) and the posterior half of the medial part of the frontal agranular cortex (PAGm), and their laminar organizations were confirmed. These connections did not appear to have a significant topographic organization. Although in areas 17 and 18b terminals or cells of origin in this fiber system were confined to the anterior half of these cortices, in area 18a they were observed spanning the anteroposterior extent of this cortex, with in part a column like organization. No evidence could be found for the participation of both the posterior parts of areas 17 and 18b and the anterior half of this frontal agranular cortex in these connections. Fibers from each subdivision of the visual cortex to the PAGm terminated predominantly in the lower part of layer I and in layer II. In area 17, this occipito-frontal projection was found to arise from the scattered pyramidal cells in layer V and more prominently from pyramidal cells in layer V of area 17/18a border. In area 18a, the fibers projecting to the PAGm originated mainly from pyramidal cells primarily in layer V and to a lesser extent in layers II, III and VI. Whereas in area 18b, this projection was found to arise mainly from pyramidal cells in layers II and III, to a lesser extent in layers V and VI, and less frequent in layer IV. On the other hand, the reciprocal projection to the visual cortex was found to originate largely from pyramidal cells in layers III and V of the PAGm. In areas 17 and 18a, these fibers terminated in layers I and VI, and in layers I, V and VI, respectively. Whereas in area 18b, they were distributed throughout all layers except layer II.

Superior colliculus-mediated visual behaviors in cat and the concept of two corticotectal systems.

Abstract: Publisher Summary This chapter is the outgrowth of a series of experiments in cat in an attempt to understand how cortex and midbrain (specifically, the superior colliculus) interact in the production of visual behaviors. A number of years ago, researchers examined how primary visual cortex affects the most visually “dominant” area of the superior colliculus (SC), its superficial laminae. This proved to be an excellent model for determining how the brain builds receptive fields from converging afferents. An extrastriate cortical area has now been identified as controlling the deep laminae SC cells that connect to those areas of the brainstem and spinal cord through which overt responses are initiated. Compromising any station along this circuit seriously impairs visual attention and orientation capability. Many of the receptive field properties of these visual cells were found to be dependent on the inputs received from primary visual cortex. This dependency is apparent when removal of striate cortex eliminated from these SC cells their binocularity, directional selectivity, and preferences for moving rather than stationary flashed.

Functional characteristics of directionally tuned neurons in the frontal visual field of the chipmunk striate cortex

Abstract: Research was performed on the intracellular activity of 150 neurons belonging to area 17 of the binocular region of the chipmunk visual cortex, showing that 65% were directionally selective and tuned (to varying degrees) to the angle of boundaries between contrasting areas and a light bar; 18% were not tuned to the direction and angle of stimulus movement, while 17% were only activated by general illumination of the receptive field. Of 39 directionally tuned neurons tested in relation to moving and stationary stimuli, 16 responded to stimulus movement only, 13 reacted to presentation of stationary bars with prolonged tonic activation, seven with a brief phasic response, and three with a phasic-tonic response. All phasic neurons were more intensively activated at higher rates of movement than tonic cells. The article considers whether an analogy may be drawn between “fast” (phasic) and “slow” (or tonic) neurons with Y- and X-systems respectively.

Functional features of receptive fields of neurons in the posterotemporal cortex of the cat

Abstract: 1. During prolonged (up to 2 h) multiple testing of the visual receptive fields of neurons in the posterotemporal cortex of the awake cat, significant fluctuations were found in form, size, and orientation in the absence of controlling experimental effects. 2. Neurons were found whose receptive fields have several separate zones (discharge centers) detected simultaneously or alternately during testing.