Showing papers on "Orientation column published in 2013"

Diverse Visual Features Encoded in Mouse Lateral Geniculate Nucleus

Abstract: The thalamus is crucial in determining the sensory information conveyed to cortex. In the visual system, the thalamic lateral geniculate nucleus (LGN) is generally thought to encode simple center-surround receptive fields, which are combined into more sophisticated features in cortex, such as orientation and direction selectivity. However, recent evidence suggests that a more diverse set of retinal ganglion cells projects to the LGN. We therefore used multisite extracellular recordings to define the repertoire of visual features represented in the LGN of mouse, an emerging model for visual processing. In addition to center-surround cells, we discovered a substantial population with more selective coding properties, including direction and orientation selectivity, as well as neurons that signal absence of contrast in a visual scene. The direction and orientation selective neurons were enriched in regions that match the termination zones of direction selective ganglion cells from the retina, suggesting a source for their tuning. Together, these data demonstrate that the mouse LGN contains a far more elaborate representation of the visual scene than current models posit. These findings should therefore have a significant impact on our understanding of the computations performed in mouse visual cortex.

Orientation-selective Responses in the Mouse Lateral Geniculate Nucleus

Abstract: The dorsal lateral geniculate nucleus (dLGN) receives visual information from the retina and transmits it to the cortex. In this study, we made extracellular recordings in the dLGN of both anesthetized and awake mice, and found that a surprisingly high proportion of cells were selective for stimulus orientation. The orientation selectivity of dLGN cells was unchanged after silencing the visual cortex pharmacologically, indicating that it is not due to cortical feedback. The orientation tuning of some dLGN cells correlated with their elongated receptive fields, while in others orientation selectivity was observed despite the fact that their receptive fields were circular, suggesting that their retinal input might already be orientation selective. Consistently, we revealed orientation/axis-selective ganglion cells in the mouse retina using multielectrode arrays in an in vitro preparation. Furthermore, the orientation tuning of dLGN cells was largely maintained at different stimulus contrasts, which could be sufficiently explained by a simple linear feedforward model. We also compared the degree of orientation selectivity in different visual structures under the same recording condition. Compared with the dLGN, orientation selectivity is greatly improved in the visual cortex, but is similar in the superior colliculus, another major retinal target. Together, our results demonstrate prominent orientation selectivity in the mouse dLGN, which may potentially contribute to visual processing in the cortex.

Cortical-Like Receptive Fields in the Lateral Geniculate Nucleus of Marmoset Monkeys

Abstract: Most neurons in primary visual cortex (V1) exhibit high selectivity for the orientation of visual stimuli. In contrast, neurons in the main thalamic input to V1, the lateral geniculate nucleus (LGN), are considered to be only weakly orientation selective. Here we characterize a sparse population of cells in marmoset LGN that show orientation and spatial frequency selectivity as great as that of cells in V1. The recording position in LGN and histological reconstruction of these cells shows that they are part of the koniocellular (K) pathways. Accordingly we have named them K-o (“koniocellular-orientation”) cells. Most K-o cells prefer vertically oriented gratings; their contrast sensitivity and TF tuning are similar to those of parvocellular cells, and they receive negligible functional input from short wavelength-sensitive (“blue”) cone photoreceptors. Four K-o cells tested displayed binocular responses. Our results provide further evidence that in primates as in nonprimate mammals the cortical input streams include a diversity of visual representations. The presence of K-o cells increases functional homologies between K pathways in primates and “sluggish/W” pathways in nonprimate visual systems.

fMRI orientation decoding in V1 does not require global maps or globally coherent orientation stimuli

Abstract: The orientation of a large grating can be decoded from V1 functional magnetic resonance imaging (fMRI) data, even at low resolution (3-mm isotropic voxels). This finding has suggested that columnar-level neuronal information might be accessible to fMRI at 3T. However, orientation decodability might alternatively arise from global orientation-bias maps. Such global maps across V1 could result from bottom-up processing, if the preferences of V1 neurons were biased toward particular orientations (e.g. radial from fixation, or cardinal, i.e. vertical or horizontal). Global maps could also arise from local recurrent or top-down processing, reflecting pre-attentive perceptual grouping, attention spreading, or predictive coding of global form. Here we investigate whether fMRI orientation decoding with 2-mm voxels requires (a) globally coherent orientation stimuli and/or (b) global-scale patterns of V1 activity. We used opposite-orientation gratings (balanced about the cardinal orientations) and spirals (balanced about the radial orientation), along with novel patch-swapped variants of these stimuli. The two stimuli of a patch-swapped pair have opposite orientations everywhere (like their globally coherent parent stimuli). However, the two stimuli appear globally similar, a patchwork of opposite orientations. We find that all stimulus pairs are robustly decodable, demonstrating that fMRI orientation decoding does not require globally coherent orientation stimuli. Furthermore, decoding remained robust after spatial high-pass filtering for all stimuli, showing that fine-grained components of the fMRI patterns reflect visual orientations. Consistent with previous studies, we found evidence for global radial and vertical bias maps in V1. However, these were weak or absent for patch-swapped stimuli, suggesting that global bias maps depend on globally coherent orientations and might arise through recurrent or top-down processes related to the perception of global form.

Demonstration of Tuning to Stimulus Orientation in the Human Visual Cortex: A High-Resolution fMRI Study with a Novel Continuous and Periodic Stimulation Paradigm

Abstract: Cells in the animal early visual cortex are sensitive to contour orientations and form repeated structures known as orientation columns. At the behavioral level, there exist 2 well-known global biases in orientation perception (oblique effect and radial bias) in both animals and humans. However, their neural bases are still under debate. To unveil how these behavioral biases are achieved in the early visual cortex, we conducted high-resolution functional magnetic resonance imaging experiments with a novel continuous and periodic stimulation paradigm. By inserting resting recovery periods between successive stimulation periods and introducing a pair of orthogonal stimulation conditions that differed by 90° continuously, we focused on analyzing a blood oxygenation leveldependent response modulated by the change in stimulus orientation and reliably extracted orientation preferences of single voxels. We found that there are more voxels preferring horizontal and vertical orientations, a physiological substrate underlying the oblique effect, and that these over-representations of horizontal and vertical orientations are prevalent in the cortical regions near the horizontal- and vertical-meridian representations, a phenomenon related to the radial bias. Behaviorally, we also confirmed that there exists perceptual superiority for horizontal and vertical orientations around horizontal and vertical meridians, respectively. Our results, thus, refined the neural mechanisms of these 2 global biases in orientation perception.

Sublinear binocular integration preserves orientation selectivity in mouse visual cortex

Abstract: Inputs from the two eyes are first combined in simple cells in the primary visual cortex. Consequently, visual cortical neurons need to have the flexibility to encode visual features under both monocular and binocular situations. Here we show that binocular orientation selectivity of mouse simple cells is nearly identical to monocular orientation selectivity in both anaesthetized and awake conditions. In vivo whole-cell recordings reveal that the binocular integration of membrane potential responses is sublinear. The sublinear integration keeps binocularly evoked depolarizations below threshold at non-preferred orientations, thus preserving orientation selectivity. Computational simulations based on measured synaptic conductances indicate that inhibition promotes sublinear binocular integration, which are further confirmed by experiments using genetic and pharmacological manipulations. Our findings therefore reveal a cellular mechanism for how visual system can switch effortlessly between monocular and binocular conditions. The same mechanism may apply to other sensory systems that also integrate multiple channels of inputs.

Cortical metabolic activity matches the pattern of visual suppression in strabismus.

Abstract: When an eye becomes deviated in early childhood, a person does not experience double vision, although the globes are aimed at different targets. The extra image is prevented from reaching perception in subjects with alternating exotropia by suppression of each eye's peripheral temporal retina. To test the impact of visual suppression on neuronal activity in primary (striate) visual cortex, the pattern of cytochrome oxidase (CO) staining was examined in four macaques raised with exotropia by disinserting the medial rectus muscles shortly following birth. No ocular dominance columns were visible in opercular cortex, where the central visual field is represented, indicating that signals coming from the central retina in each eye were perceived. However, the border strips at the edges of ocular dominance columns appeared pale, reflecting a loss of activity in binocular cells from disruption of fusion. In calcarine cortex, where the peripheral visual field is represented, there were alternating pale and dark bands resembling ocular dominance columns. To interpret the CO staining pattern, [(3)H]proline was injected into the right eye in two monkeys. In the right calcarine cortex, the pale CO columns matched the labeled proline columns of the right eye. In the left calcarine cortex, the pale CO columns overlapped the unlabeled columns of the left eye in the autoradiograph. Therefore, metabolic activity was reduced in the ipsilateral eye's ocular dominance columns which serve peripheral temporal retina, in a fashion consistent with the topographic organization of suppression scotomas in humans with exotropia.

Functional Relevance of Micromodules in the Human Association Cortex Delineated with High-Resolution fMRI

Abstract: Recent advancement of resting-state functional connectivity magnetic resonance imaging (MRI) has provided a method for drawing boundaries of brain areas. However, it remains to be elucidated how the parcellated areas in the association cortex relate to the spatial extent of the brain activation which ought to reflect a functional unit in the neural network supporting that particular function. To address this issue, in the present study, we first mapped boundaries and 2 adjacent activations in the human inferior frontal cortex, and then examined the spatial relationship between the boundaries and the 2 activations. The boundaries mapped with high-resolution functional magnetic resonance imaging revealed a collection of micromodules, the size of which was approximately only 12 mm on average, much smaller than the Brodmann areas. Each of the 2 activations associated with 2 functions, response inhibition and feedback processing, was smaller in size than the micromodules. By comparing the spatial patterns between the boundaries and the 2 activations, it was revealed that the brain activations were less likely to be located on the boundaries. These results suggest the functional relevance of the areas in the association cortex delineated by the boundary mapping method based on resting-state functional connectivity MRI.

Volumetric Seismic Dip and Azimuth Estimation With 2D Log-Gabor Filter Array

Abstract: In this paper, we propose a novel method of orientation estimation in seismic data. Unlike conventional methods of orientation estimation with a context window, our method is inspired by the neural mechanism of visual perception. The primary visual cortex in the brain contains orientation columns, which are composed of an array of orientation detectors. A log-Gabor filter with a specific orientation and scale configuration simulates the neuronal mechanism of the orientation detector, while an array of such filters simulates the orientation columns. The resulting orientation is derived at the sample level of the input seismic data: the filter response competes with each other in the array, and the maximum response defines the seismic orientation. Our proposed method has many applications in seismic interpretation, e.g., calculating the volumetric azimuth and dip attributes without picking, guiding seismic attribute computation, and detecting seismic texture patterns.

A computational study of brightness-related responses in visual cortex.

Abstract: Rossi, Rittenhouse, and Paradiso (1996) reported a cut-off at 4 Hz in the modulation amplitude of neural responses to large (up to 14°) simultaneous contrast stimuli in the striate cortex of cats, as the temporal frequency of the luminance of flanking patches increased, while the luminance of a central patch covering the neurons' classical receptive fields (CRFs) was held constant. This indicates that the modulation may involve slow processing of information in visual cortex. We develop models with a small set of parameters to explain these brightness-related responses in visual cortex. A model with any of the following mechanisms can fit the data: (a) slow local inhibition (Slow Inhibition Model); (b) slow excitation of the nodes in the second of two layers, which feed back to the inhibitory nodes in the first layer (Slow Excitation Model); and (c) conduction delays along lateral connections (Delay Model). However, the Slow Inhibition Model predicts that neurons in extrastriate cortex show similar response modulations as neurons in V1, while the Slow Excitation Model predicts that, unlike the modulations of V1 neurons shown in the experimental data, neurons in extrastriate cortex show slow modulations of responses to both the direct luminance change and the simultaneous contrast stimuli. The Delay Model predicts that the cut-off frequency of the response modulations depends on the distance from the flanker to the CRFs of the neurons. Further physiological experiments could clarify which mechanism plays an important role in the brightness-related responses in visual cortex.

Surround suppression maps in the cat primary visual cortex.

Abstract: In the primary visual cortex and higher-order areas, it is well known that the stimulation of areas surrounding the classical receptive field of a neuron can inhibit its responses. In the primate area MT, this surround suppression was shown to be spatially organized into high and low suppression modules. However, such an organization hasn’t been demonstrated yet in the primary visual cortex. Here, we used optical imaging of intrinsic signals to spatially evaluate surround suppression in the cat visual cortex. The magnitude of the response was measured in areas 17 and 18 for stimuli with different diameters, presented at different eccentricities. Delimited regions of the cortex were revealed by circumscribed stimulations of the visual field (“cortical response field”). Increasing the stimulus diameter increased the spread of cortical activation. In the cortical response field, the optimal stimulation diameter and the level of suppression were evaluated. Most pixels (3/4) exhibited surround suppression profiles. The optimal diameter, corresponding to a population of receptive fields, was smaller in area 17 (22 deg.) than in area 18 (36 deg.) in accordance with electrophysiological data. No difference in the suppression strength was observed between both areas (A17: 25%, A18: 21%). Further analysis of our data revealed the presence of surround modulation maps, organized in low and high suppression domains. We also developed a statistical method to confirm the existence of this cortical map and its neuronal origin. The organization for center/surround suppression observed here at the level of the primary visual cortex is similar to those found in higher order areas in primates (e.g. area MT) and could represent a strategy to optimize figure ground discrimination.

Why Neurons Are Not the Right Level of Abstraction for Implementing Cognition

Abstract: The cortex accounts for 70% of the brain volume. The human cortex is made of micro-columns, arrangements of 110 cortical neurons (Mountcastle), grouped in by the thousand in so-called macro-colums (or columns) which belong to the same functional unit as exemplified by Nobel laureates Hubel and Wiesel with the orientation columns of the primary visual cortex. The cortical column activity does not exhibit the limitations of single neurons: activation can be sustained for very long periods (sec.) instead of been transient and subject to fatigue. Therefore, the cortical column has been proposed as the building block of cognition by several researchers, but to not effect – since explanations about how the cognition works at the column level were missing. Thanks to the Theory of neural Cognition, it is no more the case.

A spatialized model of textures perception using structure tensor formalism

Abstract: The primary visual cortex (V1) can be partitioned into fundamental domains or hypercolumns consisting of one set of orientation columns arranged around a singularity or ''pinwheel'' in the orientation preference map A recent study on the specific problem of visual textures perception suggested that textures may be represented at the population level in the cortex as a second-order tensor, the structure tensor, within a hypercolumn In this paper, we present a mathematical analysis of such interacting hypercolumns that takes into account the functional geometry of local and lateral connections The geometry of the hypercolumn is identified with that of the Poincare disk $\D$ Using the symmetry properties of the connections, we investigate the spontaneous formation of cortical activity patterns These states are characterized by tuned responses in the feature space, which are doubly-periodically distributed across the cortex

A spatialized model of visual texture perception using the structure tensor formalism

Abstract: The primary visual cortex (V1) can be partitioned into fundamental domains or hypercolumns consisting of one set of orientation columns arranged around a singularity or ``pinwheel'' in the orientation preference map. A recent study on the specific problem of visual textures perception suggested that textures may be represented at the population level in the cortex as a second-order tensor, the structure tensor, within a hypercolumn. In this paper, we present a mathematical analysis of such interacting hypercolumns that takes into account the functional geometry of local and lateral connections. The geometry of the hypercolumn is identified with that of the Poincare disk $\mathbb{D}$. Using the symmetry properties of the connections, we investigate the spontaneous formation of cortical activity patterns. These states are characterized by tuned responses in the feature space, which are doubly-periodically distributed across the cortex.

Bio-inspired orientation analysis for seismic image

Abstract: In this paper, we propose a novel method of orientation analysis for seismic image. Unlike conventional methods of orientation estimation with a context window, our method is inspired by the neural mechanism of visual perception in the biological brain. In the brain, the primary visual cortex contains orientation columns, which is composed of an array of simple cells as orientation detectors. A log-Gabor filter with a specific orientation and scale configuration simulates the neuronal mechanism of the simple cell, while an array of such orientation detectors simulates the neuronal responses of the orientation columns. The resulting orientation is derived at the pixel level of the input seismic image: the neuronal response of each simple cell competes with other cells in the same orientation column for the same pixel, and the winning neuron with maximum response defines the perceived orientation. We applied the proposed method to seismic interpretation to analyze the orientation patterns, and it also can be used as a general image orientation analysis tool.

Inferring retinal ganglion cell mosaics from measured orientation preference maps in cat V1

Abstract: It has been argued that the emergence of roughly periodic orientation preference maps (OPMs) in the primary visual cortex (V1) of carnivores and primates can be explained by a so-called statistical connectivity model. This model assumes that input to V1 neurons is dominated by feed-forward projections originating from a small set of retinal ganglion cells (RGCs). The typical spacing between adjacent cortical orientation columns preferring the same orientation then arises via Moire-Interference between hexagonal ON/OFF RGC mosaics. While this Moire-Interference critically depends on long-range hexagonal order within the RGC mosaics, a recent statistical analysis of RGC receptive field positions found no evidence for such long-range positional order. Hexagonal order may be only one of several ways to obtain spatially repetitive OPMs in the statistical connectivity model. Here, we investigate a more general requirement on the spatial structure of RGC mosaics that can seed the emergence of spatially repetitive cortical OPMs, namely that angular correlations between so-called RGC dipoles exhibit a spatial structure similar to that of OPM autocorrelation functions. Both in cat beta cell mosaics as well as primate parasol receptive field mosaics we find that RGC dipole angles are spatially uncorrelated. To help assess the level of these correlations, we introduce a novel point process that generates mosaics with realistic nearest neighbor statistics and a tunable degree of spatial correlations of dipole angles. Using this process, we show that given the size of available data sets, the presence of even weak angular correlations in the data is very unlikely. We conclude that the layout of ON/OFF ganglion cell mosaics lacks the spatial structure necessary to seed iso-orientation domains in the primary visual cortex.

Alpha and Beta Oscillations in the Dynamics of the Areas and Weightings of the Receptive Fields of Striate Neurons in Cats in Classical and Combined Mapping

Abstract: Acute experiments on 22 anesthetized and immobilized cats were performed to produce dynamic time-slices maps of 83 on and/or off receptive fields of 47 visual cortex field 17 neurons using classical and combined mapping. These experiments showed that the areas and weightings of neuron fields during response generation using classical mapping changed in a wavelike manner. Mathematical processing of these data showed that the dynamics of receptive field characteristics consisted of the sum of a slow aperiodic and a rapid periodic component. The slow aperiodic component showed biphasic receptive field dynamics. The oscillation frequency of the periodic component in most cases was distributed into the alpha and, more rarely, beta EEG ranges. Additional activation of the discharge center of the receptive field of the neuron in combined mapping had no effect on the frequency of periodic oscillations but elicited significant reductions in the duration and amplitude of the aperiodic component. The mechanisms underlying the dynamics of neuron receptive fields in the primary visual cortex are discussed, as is the functional significance of these dynamics.