Showing papers on "Orientation column published in 1991"

Synchronization of oscillatory neuronal responses between striate and extrastriate visual cortical areas of the cat

Abstract: Recent studies have shown that neurons in area 17 of cat visual cortex display oscillatory responses which can synchronize across spatially separate orientation columns. Here, we demonstrate that unit responses recorded from the posteromedial lateral suprasylvian area, a visual association area specialized for the analysis of motion, also exhibit an oscillatory temporal structure. Cross-correlation analysis of unit responses reveals that cells in area 17 and the posteromedial lateral suprasylvian area can oscillate synchronously. Moreover, we find that the interareal synchronization is sensitive to features of the visual stimuli, such as spatial continuity and coherence of motion. These results support the hypothesis that synchronous neuronal oscillations may serve to establish relationships between features processed in different areas of visual cortex.

The neural basis of visual function

Abstract: Topography of visual cortical area in cats and primates electrophysiological basis of eye movements in primates functional properties of the different classes of retinal ganglion cells receptive field structure of retinal ganglion cells in cats and monkeys electrophysiology of the LGNs in higher mammals inhibitory mechanisms in the visual cortex electrophysiology of the superior colliculus in subprimate species electrophysiolgy of the superior colliculus in subprimate species electrophysiology of the inner nuclear and inner plexiform layers of the retina the accessory optic system electrophysiology of the pulvinar in higher mammals quantitative electrophysiology of visual cortical neurons cat area 17 - laminer organization electrophysiology studies of the columnar organization of the visual cortex in higher mammals electrophysiology of colour vision in the retinogeniculocortical pathways intracellular recordings in visual pathways receptive field properties of extrastriate cortical neurons in subprimate species afferent inputs and receptive field properties of cells in different layers of striate cortex in cat and monkey receptive field structure of cells in visual cortex electrophysiology of vision beyond extrastriate cortex.

Relation of cortical cell orientation selectivity to alignment of receptive fields of the geniculocortical afferents that arborize within a single orientation column in ferret visual cortex.

Abstract: Neurons in the primary visual cortex of higher mammals are arranged in columns, and the neurons in each column respond best to light-dark borders of particular orientations. The basis of cortical cell orientation selectivity is not known. One possible mechanism would be for cortical cells to receive input from several lateral geniculate nucleus (LGN) neurons with receptive fields that are aligned in the visual field (Hubel and Wiesel, 1962). We have investigated the relationship between the arrangement of the receptive fields of geniculocortical afferents and the orientation preferences of cortical cells in the orientation columns to which the afferents provide visual input. Radial microelectrode penetrations were made into primary visual cortex of anesthetized adult sable ferrets. Cortical cells were recorded throughout the depth of the cortex, and their orientation preferences were determined. Cortical cell responses were then eliminated by superfusion of the cortex with either kainic acid (Zahs and Stryker, 1988) or muscimol. After the drug treatment, responses from many single units with distinct receptive fields were recorded. These responses were presumed to be those of geniculocortical afferents, because they had the response properties characteristic of LGN neurons, and because they could be recorded only in cortical layers that receive geniculate input. In 16 of 18 cases, the afferent receptive fields recorded in a single penetration covered an elongated region of visual space. In these penetrations, the best-fit line through the centers of the afferent receptive fields generally paralleled the preferred orientation of cortical cells recorded at the same site in cortex. These results are consistent with the Hubel and Wiesel (1962) model for the construction of oriented visual cortical receptive fields from geniculate inputs with aligned receptive fields.

A detailed model of the primary visual pathway in the cat: comparison of afferent excitatory and intracortical inhibitory connection schemes for orientation selectivity

Abstract: In order to arrive at a quantitative understanding of the dynamics of cortical neuronal networks, we simulated a detailed model of the primary visual pathway of the adult cat. This computer model comprises a 5 degrees x 5 degrees patch of the visual field at a retinal eccentricity of 4.5 degrees and includes 2048 ON- and OFF-center retinal beta-ganglion cells, 8192 geniculate X-cells, and 4096 simple cells in layer IV in area 17. The neurons are implemented as improved integrate-and-fire units. Cortical receptive fields are determined by the pattern of afferent convergence and by inhibitory intracortical connections. Orientation columns are implemented continuously with a realistic receptive field scatter and jitter in the preferred orientations. We first show that realistic ON-OFF-responses, orientation selectivity, velocity low-pass behaviour, null response, and responses to spot stimuli can be obtained with an appropriate alignment of geniculate neurons converging onto the cortical simple cell (Hubel and Wiesel, 1962) and in the absence of intracortical connections. However, the average receptive field elongation (length to width) required to obtain realistic orientation tuning is 4.0, much higher than the average observed elongation. This strongly argues for additional intracortical mechanisms sharpening orientation selectivity. In the second stage, we simulated five different inhibitory intracortical connection patterns (random, local, sparse-local, circular, and cross-orientation) in order to investigate the connection specificity necessary to achieve orientation tuning. Inhibitory connection schemes were superimposed onto Hubel and Wiesel-type receptive fields with an elongation of 1.78. Cross-orientation inhibition gave rise to different horizontal and vertical orientation tuning curves, something not observed experimentally. A combination of two inhibitory schemes, local and circular inhibition (a weak form of cross-orientation inhibition), is in good agreement with observed receptive field properties. The specificity required to establish these connections during development is low. We propose that orientation selectivity is caused by at least three different mechanisms (“eclectic” model): a weak afferent geniculate bias, broadly tuned cross-orientation inhibition, and some iso-orientation inhibition. The most surprising finding is that an isotropic connection scheme, circular inhibition, in which a cell inhibits all of its postsynaptic target cells at a distance of approximately 500 microns, enhances orientation tuning and leads to a significant directional bias. This is caused by the embedding of cortical cells within a columnar structure and does not depend on our specific assumptions.

Effects of binocular deprivation on the development of clustered horizontal connections in cat striate cortex.

Abstract: Intrinsic horizontal axon collaterals in the striate cortex of adult cats specifically link columns having the same preferred orientation; consequently, retrograde tracer injections result in intrinsic labeling that is sharply clustered. We have previously shown that the normal development of this circuitry involves the emergence of crude clusters from an unclustered pattern during the second postnatal week. Crude clusters are later refined to the adult level of specificity by the selective rearrangement of axonal arbors that initially project to incorrect orientation columns. Here we report that depriving animals of patterned visual experience by binocular lid suture prior to natural eye opening had no discernible effect on the emergence of crude clusters. In contrast, cluster refinement was dramatically affected by binocular deprivation. Injections of retrograde tracers in the striate cortex of animals binocularly deprived for greater than 1 month revealed only crude clusters, indicating that horizontal axon collaterals projecting to incorrect orientation columns were retained well past the age when they normally would have been eliminated. Layer 2/3 pyramidal cells from 6-week-old binocularly deprived animals had abnormal distributions of intrinsic horizontal axon collaterals that mirrored the lack of cluster refinement. The radial clustering of their horizontal collaterals was considerably less precise than normal. These cells, nevertheless, developed many of the features of normal mature arbors, including the distal axonal branches not seen in arbors from younger animals with normal visual experience. Together, these results indicate that axonal rearrangements occurred, but with reduced specificity. Thus, binocular deprivation did not simply arrest the development of this orientation-specific circuit at an immature state but limited the accuracy with which axon collaterals were added or eliminated. We suggest that development of this orientation-specific circuitry, like ocular dominance column segregation, may depend on temporal correlation of activity for regulation of axonal rearrangement. The specificity of rearrangement may be degraded in binocularly deprived cats because they do not experience sharply oriented visual stimuli necessary for concurrent activation of same-orientation columns.

Single-unit and 2-deoxyglucose studies of side inhibition in macaque striate cortex.

Abstract: In the course of studies to map spatial frequency tuning of neurons in layers 2 and 3 of macaque striate cortex, we found that a high proportion (70%) of cells in the interblob regions responded poorly to full-field gratings, compared with responses to single bars, edges, or delimited gratings. This was most often due to side inhibition, in which increasing the number of cycles of a grating placed within the cell's receptive field causes progressive inhibition of response. Quantitative receptive-field mappings showed, however, that the inhibition can occur within the region activated by a bar, as well as beyond it. The inhibition appears to be orientation-selective, in that a surround grating was more effective at inhibiting the response to a center grating patch if it was of similar orientation. 2-Deoxyglucose experiments confirmed that side inhibition is very widespread in the interblobs of layers 2 and 3 and suggested that it is reduced or lacking in layers 4A through 6. Since layers 2 and 3 of striate cortex are the major source of cortical projections to area V2 and beyond, the prevalence of side stopping in these laminae has implications for theories of cortical visual function. Side-stopped interblob cells may be acting as "contour-pass filters" that filter out redundant information in textured or noisy surfaces, focusing subsequent form processing on contrasts corresponding to object boundaries.

Coverage and the design of striate cortex

Abstract: Hubel and Wiesel (1977) suggested that ocular dominance and orientation columns in the macaque monkey striate cortex might be bands of uniform width that intersected orthogonally. They pointed out that if this were the case, there would be an equal allocation of cells of different orientation preference to each eye and to each point in visual space. However, orientation and ocular dominance columns have a more complex structural organization than is implied by this model: for example, iso-orientation domains do not intersect ocular dominance stripes at right angles and the two columnar systems have different periodicities. This raises the question as to how well the striate cortex manages to allocate equal numbers of neurons of different orientation preference to each eye and to each region of visual space, a factor referred to here as coverage. This paper defines a measure of uniformity of coverage, c?, and investigates its dependence on several different parameters of columnar organisation. Calculations were done first using a simplified one-dimensional model of orientation and ocular dominance columns and were then repeated using more realistic two-dimensional models, generated with the algorithms described in the preceding paper (Swindale 1991). Factors investigated include the relative periodicities of the two columnar systems, the size of the cortical point image, the width of orientation tuning curves, whether columns are spatially anisotropic or not, and the role of the structural relationships between columns described by Blasdel and Salama (1986). The results demonstrate that coverage is most uniform when orientation hypercolumns are about half the size of ocular dominance hypercolumns. Coverage is most uneven when the hypercolumns are the same size, unless they are related in the way described by Blasdel and Salama, in which case coverage gets only slightly worse as the size ratio (ori/od) increases above 0.5. The minimum diameter of cortical point image that ensures reasonably uniform coverage is about twice the size of an ocular dominance hypercolumn i.e. about 1.5---2.0 mm.

Isotropic connections generate functional asymmetrical behavior in visual cortical cells.

Abstract: 1. We study the relationship between structure and function in inhibitory long-range interactions in visual cortex. The sharpening of orientation tuning with "cross-orientation inhibition" is used as an example to discuss anisotropies that are generated by long-range connections. 2. In this study, as opposed to the detailed cortex model described in a previous report, a model of the cortical orientation column structure is proposed in which cortical cells are described only by their orientation preference. 3. We present results using different geometric arrangements of orientation columns. In the simplest case, straight parallel orientation columns were used. We also utilized more realistic, curved columns generated by a simple algorithm. The results were confirmed by the study of a patch of real column structure, determined experimentally by Swindale et al. 4. A given cell receives functionally defined cross-orientation inhibition if the cell receives inhibitory input that is strongest along its nonpreferred orientation. On the other hand, a cell is said to receive structurally defined cross-orientation inhibition if the inhibition arises from source cells with an orientation preference orthogonal to that of the target cell. Even though those definitions seem to describe similar situations, we show that, in the general case, structurally defined cross-orientation inhibition does not efficiently sharpen orientation selectivity. In particular, for straight and parallel columns, structurally defined cross-orientation inhibition results in unequal amounts of inhibition for whole cell populations with different preferred orientations. 5. In more realistic column structures, we studied the question of whether structural cross-orientation inhibition could be implemented in a more efficient way. However, for the majority of cells, it is demonstrated that their nonpreferred stimulus will not preferably excite "cross-oriented" cells. Thus structural cross-orientation inhibition is not efficient in real cortical columns. 6. We propose a new mechanism called circular inhibition. In this connection scheme, a target cell receives inhibitory input from source cells that are located at a given distance (the same for all cells) from the target cell. Circular inhibition can be regarded as two-dimensional long-range lateral inhibition. As opposed to structural cross-orientation inhibition, this mechanism does not introduce unwanted anisotropies in the orientation tuning of the target cells. It is also conceptually much simpler and developmentally advantageous. It is shown that this connection scheme results in a net functional cross-orientation inhibition in all realistic column geometries. The inhibitory tuning strength obtained with circular inhibition is weak and similar to that measured in reality.(ABSTRACT TRUNCATED AT 400 WORDS)

Figure-ground separation: evidence for asynchronous processing in visual perception?

Abstract: The performance of the human visual system in extracting noisy figures from a noisy background is astonishingly good. Even in situations of very poor contrast, boundaries emerge clearly. Conversely, typical edge detectors fail to give good results for such images. In an attempt to explain the discrepancies in these performances we have developed a neural network model relying on two assumptions, both of which are based on neurophysiological findings. Firstly, the processing of visual information is considered ta be asynchronous: stimuli are delayed accordingly to their intensity. Secondly, emergent boundaries have the property of producing coherent responses corresponding to the (near)-simultaneous responses of cells in the cortical orientation columns. Results show that such neural network can indeed benefit from the asynchrony when treating images with ratio signal-to-noise particularly low.

Orientation and Color Columns in Monkey Striate Cortex

Abstract: The parallel stripe model of orientation columns in monkey striate cortex was first proposed by Hubel and Wiesel (1972) as part of an anatomical lesion study of projections from parvo and magnocellular layers of the lateral geniculate nucleus (LGN) to the cortex. This paper demonstrated ocular dominance columns (in the form of parallel stripes) in striate cortex, a given stripe receiving input from either layer 5 or layer 6 of the LGN, whose inputs in turn derive from the ipsilateral and contralateral eyes, respectively. There was no evidence in the paper for any particular arrangement of orientation columns, but it was proposed that orientation columns might take the form of parallel stripes running orthogonal to the ocular dominance stripes. There has been no evidence since then to support the existence of the parallel stripe orientation column model in monkeys, but it has somehow persisted, in the absence of any better model to replace it. Hubel still chose to include it, with a new name (the ‘ice cube’ model), in his recent book (Hubel, 1988). In fact, the model has not changed in 16 years.

Unsupervised learning for the visual cortex (layer IV): model and simulations

Abstract: The authors present a statistical model to study the evolution of orientation columns in layer IV of the visual cortex after birth by simulating, on the retina, the first visual experiences of an animal (darkness, biased, and normal visual environments). The results are consistent with biological experiments. The authors show the necessity of introducing a new nonlinear model in which both vertical and intracortical connections evolve simultaneously as soon as the visual experience begins. The model sets up intracortical connections and achieves the maturation of orientation columns. It takes into account recent neurobiological observations for the development of intracortical connections. Simulations reproduce the results of experiments which observe excitative intracortical connections between cells of similar orientation in different hypercolumns. >

Single-unit and 2-deoxyglucose studies of side inhibition in macaque striate cortex (visual cortex/side stopping/side-band inhibition/surround inhibition/contour perception)

Abstract: In the course of studies to map spatial fre- quency tuning of neurons in layers 2 and 3 of macaque striate cortex, we found that a high proportion (70%) of cells in the interblob regions responded poorly to full-field gratings, com- pared with responses to single bars, edges, or delimited grat- ings. This was most often due to side inhibition, in which increasing the number of cycles of a grating placed within the cell's receptive field causes progressive inhibition of response. Quantitative receptive-field mappings showed, however, that the inhibition can occur within the region activated by a bar, as well as beyond it. The inhibition appears to be orientation- selective, in that a surround grating was more effective at inhibiting the response to a center grating patch if it was of similar orientation. 2-Deoxyglucose experiments confirmed that side inhibition is very widespread in the interblobs of layers 2 and 3 and suggested that it is reduced or lacking in layers 4A through 6. Since layers 2 and 3 of striate cortex are the major source of cortical projections to area V2 and beyond, the prevalence of side stopping in these laminae has implica- tions for theories of cortical visual function. Side-stopped interblob cells may be acting as "contour-pass filters" that filter out redundant information in textured or noisy surfaces, focusing subsequent form processing on contrasts correspond- ing to object boundaries.

The Design of Striate Cortex

Abstract: Our lack of knowledge about the functions of most regions of the brain makes it difficult to discuss how different parts of it may have evolved, and why particular brain regions are differently organised in different species. It is relatively easy to understand why the shape of a bird’s beak varies from one species to the next, since the function of the beak is understood, but why is the lateral geniculate nucleus of a monkey organised differently from that of a cat or a mouse? A satisfactory explanation of the evolution of the lateral geniculate nucleus (or that of almost any other brain region) is impossible because we have very little idea of what the nucleus is for. Although discussing the evolution of the striate cortex may seem an equally impossible task, we do have some ideas about its possible function, thanks mainly to the work of Hubel and Wiesel, and my purpose in this chapter is to discuss one of their suggestions about what striate cortex does, and to show how this may have influenced some aspects of its design or evolution.

A functional model of spectral orientation columns in the primary auditory cortex.

Abstract: A functional model of the primary auditory cortex is proposed based on physiological maps of the response area organization in ferret AI [S A Shamma, J W Fleshman, and P Wiser, J Neurophysiol (submitted for publication)] Systematic changes in the excitatory and inhibitory portions of the response areas along the isofrequency planes are approximated by a difference of Gaussian function with spatially changing parameters The fundamental functional principle that emerges from the analysis of the model is that the primary auditory cortex encodes the shape of the acoustic spectrum in the distribution of its responses along the isofrequency planes Specifically, it maps to each isofrequency plane a normalized measure of the locally averaged gradient of the input spectrum at that frequency Physiological and psychoacoustical correlates and implications of these findings are explained Parallels to the functional organization of the visual cortex are also discussed

Backward conditioned connection and inhibitory reorganization of the receptive fields of cortical neurons as the basis of subconscious change in the thresholds of visual recognition and detection.

Abstract: Three groups of facts are compared in this study: the significant adaptive and adaptational modification of the receptive fields of neurons of the visual cortex of the cat, the conditioned, selective, subsensory change in the threshold of perception (detection and recognition) by an individual of a letter in relation to two control letters, and the role of spatially-specialized cortical inhibition in the formation and adaptive modifications of the receptive fields and detector properties of neurons of the visual cortex. The relationship of the described phenomena and the commonality of their mechanisms is discussed.