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Parallel visual pathways from the retina to the primary visual cortex (V1) via the lateral geniculate nucleus are common to many mammalian species, including mice, carnivores, and primates. However, it remains unclear which visual features present in both retina and V1 may be inherited from parallel pathways versus extracted by V1 circuits in the mouse. Here, using calcium imaging and rabies circuit tracing, we explore the relationships between tuning of layer 4 (L4) V1 neurons and their retinal ganglion cell (RGC) inputs. We find that subpopulations of L4 V1 neurons differ in their tuning for direction, orientation, spatial frequency, temporal frequency, and speed. Furthermore, we find that direction-tuned L4 V1 neurons receive input from direction-selective RGCs, whereas orientation-tuned L4 V1 neurons receive input from orientation-selective RGCs. These results suggest that direction and orientation tuning of V1 neurons may be partly inherited from parallel pathways originating in the retina. [Display omitted] • Direction-selective (DS) layer 4 (L4) V1 neurons receive more input from DS RGCs • Orientation-selective (OS) L4 V1 neurons receive more input from OS RGCs • DS L4 V1 neurons receive more input from the dLGN shell than OS L4 V1 neurons • L4 V1 neurons with different spatiotemporal tuning reside at different depths in L4 Wang et al. find that direction-selective (DS) layer 4 (L4) V1 neurons receive more input from DS retinal ganglion cells (RGCs), whereas orientation-selective (OS) L4 V1 neurons receive more input from OS RGCs, suggesting that the tuning of L4 V1 neurons may be partly generated by retinal input. [ABSTRACT FROM AUTHOR]

The effects of ethanol on brain function have been extensively studied using a variety of in vitro and in vivo techniques. For example, electrophysiological studies using brain slices from rodents and non-human primates have demonstrated that acute and chronic exposure to ethanol alters the intrinsic excitability and synaptic signaling of neurons within cortical and sub-cortical areas of the brain. In humans, neuroimaging studies reveal alterations in measures of brain activation and connectivity in subjects with alcohol use disorder. While complementary, these methods are inherently limited due to issues related to either disruption of normal sensory input (in vitro slice studies) or resolution (whole brain imaging). In the present study, we used 2-photon laser scanning microscopy in intact animals to assess the impact of chronic ethanol exposure on sensory-evoked neuronal and vascular responses. Adult male C57BL/6J mice were exposed to four weekly cycles of chronic intermittent ethanol (CIE) exposure, while control mice were exposed to air. After withdrawal (≥72 h), a cranial window was placed over the primary visual cortex (V1), and sensory-evoked responses were monitored using the calcium indicator OGB-1. CIE exposure produced small but significant changes in response amplitude (decrease) and orientation selectivity of V1 neurons (increase). While arteriole diameter did not differ between control and CIE mice under baseline conditions, sensory-evoked dilation was enhanced in vessels from CIE-exposed mice as compared to controls. This was accompanied by a reduced latency in response to stimulation. In separate experiments, pial arteriole diameter was measured in the barrel cortex of control and CIE-exposed mice. Baseline diameter of barrel cortex arterioles was similar between control and CIE-exposed mice, but unlike vessels in V1, sensory-evoked dilation of barrel cortex arterioles was similar between the two groups. Together, the results of these studies suggest that chronic exposure to alcohol induces changes in neurovascular coupling that are region-dependent. [ABSTRACT FROM AUTHOR]

Although our brain and deep neural networks (DNNs) can perform high-level sensory-perception tasks, such as image or speech recognition, the inner mechanism of these hierarchical information-processing systems is poorly understood in both neuroscience and machine learning. Recently, Morcos et al. (2018) examined the effect of class-selective units in DNNs, i.e., units with high-level selectivity, on network generalization, concluding that hidden units that are selectively activated by specific input patterns may harm the network's performance. In this study, we revisited their hypothesis, considering units with selectivity for lower-level features, and argue that selective units are not always harmful to the network performance. Specifically, by using DNNs trained for image classification, we analyzed the orientation selectivity of individual units, a low-level selectivity widely studied in visual neuroscience. We found that orientation-selective units exist in both lower and higher layers of these DNNs, as in our brain. In particular, units in lower layers became more orientation-selective as the generalization performance improved during the course of training. Consistently, networks that generalized better were more orientation-selective in the lower layers. We finally revealed that ablating these selective units in the lower layers substantially degraded the generalization performance of the networks, at least by disrupting the shift-invariance of the higher layers. These results suggest that orientation selectivity can play a causally important role in object recognition, and that, contrary to the triviality of units with high-level selectivity, lower-layer units with selectivity for low-level features may be indispensable for generalization, at least for the several network architectures. [ABSTRACT FROM AUTHOR]

Abstract In the cortex, demarcated unimodal sensory regions often respond to unforeseen sensory stimuli and exhibit plasticity. The goal of the current investigation was to test evoked responses of primary visual cortex (V1) neurons when an adapting auditory stimulus is applied in isolation. Using extracellular recordings in anesthetized cats, we demonstrate that, unlike the prevailing observation of only slight modulations in the firing rates of the neurons, sound imposition in isolation entirely shifted the peaks of orientation tuning curves of neurons in both supra- and infragranular layers of V1. Our results suggest that neurons specific to either layer dynamically integrate features of sound and modify the organization of the orientation map of V1. Intriguingly, these experiments present novel findings that the mere presentation of a prolonged auditory stimulus may drastically recalibrate the tuning properties of the visual neurons and highlight the phenomenal neuroplasticity of V1 neurons. Highlights • Prolonged application of sound shifts preferred orientation of neurons in area 17 of cats. • Orientation tuning shifts in the individual neurons in supra- and infragranular layers of V1. • Supra- and infragranular layers of V1 operate together but also as distinct compartments following sound adaptation. • Visual cortex is specifically and dynamically impacted by non-visual stimuli. • Sound adaptation certainly modifies the organization of orientation maps in V1. [ABSTRACT FROM AUTHOR]

Orientation selectivity is an important feature of visual cortical neurons. Optical imaging of the visual cortex allows for the generation of maps of orientation selectivity that reflect the activity of large populations of neurons. To estimate the statistical significance of effects of experimental manipulations, evaluation of the stability of cortical maps over time is required. Here, we performed optical imaging recordings of the visual cortex of anesthetized adult cats. Monocular stimulation with moving clockwise square-wave gratings that continuously changed orientation and direction was used as the mapping stimulus. Recordings were repeated at various time intervals, from 15 min to 16 h. Quantification of map stability was performed on a pixel-by-pixel basis using several techniques. Map reproducibility showed clear dynamics over time. The highest degree of stability was seen in maps recorded 15–45 min apart. Averaging across all time intervals and all stimulus orientations revealed a mean shift of 2.2 ± 0.1°. There was a significant tendency for larger shifts to occur at longer time intervals. Shifts between 2.8° (mean ± 2SD) and 5° were observed more frequently at oblique orientations, while shifts greater than 5° appeared more frequently at cardinal orientations. Shifts greater than 5° occurred rarely overall (5.4% of cases) and never exceeded 11°. Shifts of 10–10.6° (0.7%) were seen occasionally at time intervals of more than 4 h. Our findings should be considered when evaluating the potential effect of experimental manipulations on orientation selectivity mapping studies. [ABSTRACT FROM AUTHOR]

The simple cells of the visual cortex respond over a narrow range of stimulus orientations, and this tuning is invariant to the contrast at which the stimulus is presented. The inputs to a single cell derive from a population of thalamic cells that provide a bell-shaped tuning width and offset that increases with stimulus contrast. Synaptic depression, noise and inhibition have been proposed as feedforward mechanisms to explain why these increases do not appear in simple cells. The extent to which these three mechanisms contribute to contrast-invariant orientation tuning is unknown. Consequently, the aim was to test the hypothesis that these mechanisms do not contribute equally. Unlike previous studies, all mechanisms were examined using the same network model based on Banitt et al. (2007). The results showed that thalamocortical synaptic noise was essential and sufficient to widen tuning widths at low contrasts to that of higher contrasts but could not counteract the offset at higher contrasts. Thalamocortical synaptic depression could only be used to counteract a small fraction of the offset otherwise the relationship between contrast and response rate was disrupted. Only broadly tuned simple and complex cell inhibition could counteract the remaining offset for all stimulus contrasts but complex cell inhibition reduced the gain of the response. These results suggest unequal contributions of these feedforward mechanisms with thalamic synaptic noise widening tuning widths for low contrasts, synaptic depression counteracting a small component of the offset and synaptic inhibition completely removing the remaining offset to produce contrast-invariant orientation tuning. [ABSTRACT FROM AUTHOR]

Cerebral cortex contains various types of GABAergic neurons exerting local inhibition. Although the number of GABAergic inhibitory neurons is much smaller than glutamatergic excitatory neurons, they show greater diversity in their morphological and physiological properties. Genetic markers for distinct sub-classes of GABAergic neurons have been identified, and technical advances achieved in the past few decades have brought about a demonstration of a unique function of each sub-class of GABAergic neurons in the cortex. In particular, visual processing in the cortex requires inhibitory function of various GABAergic neurons. Here, we summarize current understandings on the function of inhibitory neurons in the cortex, especially focusing on their roles in visual processing. [ABSTRACT FROM AUTHOR]

Bipolar cells (BCs) are integral to the retinal circuits that extract diverse features from the visual environment. They bridge photoreceptors to ganglion cells, the source of retinal output. Understanding how such circuits encode visual features requires an accounting of the mechanisms that control glutamate release from bipolar cell axons. Here, we demonstrate orientation selectivity in a specific genetically identifiable type of mouse bipolar cell—type 5A (BC5A). Their synaptic terminals respond best when stimulated with vertical bars that are far larger than their dendritic fields. We provide evidence that this selectivity involves enhanced excitation for vertical stimuli that requires gap junctional coupling through connexin36. We also show that this orientation selectivity is detectable postsynaptically in direction-selective ganglion cells, which were not previously thought to be selective for orientation. Together, these results demonstrate how multiple features are extracted by a single hierarchical network, engaging distinct electrical and chemical synaptic pathways. [Display omitted] • BC5A axon terminals respond best to vertically oriented features • BC5A terminal orientation tuning relies on connexin 36-containing gap junctions • Vertically orientated wide-field amacrine cell processes contact BC5A axon terminals • BC5A tuning shapes orientation selectivity in postsynaptic DSGCs Hanson and colleagues demonstrate that glutamatergic excitatory inputs to classic ON-OFF direction-selective ganglion cells are tuned for orientation by being electrically coupled to a set of wide-field amacrine cells with vertically oriented processes. Thus, orientation and direction-selective information may be encoded by a single retinal neuron, like in the visual cortex. [ABSTRACT FROM AUTHOR]

Electrophysiological recordings in cat and mouse V1 reveal that ketamine influence depends on the post-adaptation shift amplitude. It alters the orientation selectivity acquired following adaptation and induces plasticity in the primary visual cortex in both species, even though they exhibit different organization of V1. In addition, ketamine adjusts the configuration of involved connectomes. [Display omitted] • The effects of visual adaptation on the preferred orientation are not maintained after ketamine application. • Ketamine alters the functional connectivities established after visual adaptation. • Ketamine increases spike synchronization in cat but not in mouse. Adult primary visual cortex features well demonstrated orientation selectivities. However, the imposition of a non-preferred stimulus for many minutes (adaptation) or the application of an antidepressant drug, such as ketamine, shifts the peak of the tuning curve, assigning a novel selectivity to a neuron. The effect of ketamine on V1 neural circuitry is not yet ascertained. The present investigation explores (in control, post-adaptation, and following local ketamine application) the modification of orientation selectivities and its outcome on functional relationships between neurons in mouse and cat. Two main results are revealed. Electrophysiological neuronal responses of monocular stimulation show that in cells exhibiting large orientation shifts after adaptation, ketamine facilitates the cell's recovery. Whereas in units displaying small shifts following adaptation, the drug increases the magnitude of orientation shifts. In addition, pair-wise cross correlogram analyses show modifications of functional relationships between neurons revealing updated micro-circuits as a consequence of ketamine application. We report in cat but not in mouse, that ketamine significantly increases the connectivity rate, their strengths, and an enhancement of neuronal synchrony. [ABSTRACT FROM AUTHOR]

In spite of the fact that the functional organization of primary visual cortices (V1) differs across species, the dynamic of orientation selectivity is highly structured within neuronal populations. In fact, neurons functionally connect each other in an organized Hebbian process, wherein their wiring and firing are intimately related. Moreover, neuronal ensembles have been suggested to be strongly implicated in sensory processing. Within these ensembles, neurons may be sharply or broadly tuned in relation to the stimulus. Therefore, it is important to determine the relationship between the response selectivity of neurons and their functional connectivity pattern across species. In the present investigation, we sought to compare the stimulus-evoked functional connectivity between the broadly tuned and the sharply tuned neurons in two species exhibiting different cortical organization for orientation selectivity: cats (columnar-organized) and mice (salt-and-pepper organization). In addition, we examined the distribution of connectivity weights within cell-assemblies in the visual cortex during visual adaptation. First, we report that the sharply tuned neurons exhibited higher synchrony index than the broadly tuned cells in the cat visual cortex. On the contrary, in mice, the broadly tuned cells displayed higher connectivity index. Second, a significant correlation was found between the connectivity strength and the difference of preferred orientations of neurons for both species. Finally, we observed a systematic adjustment of the connectivity weights within neuronal ensembles in mouse primary visual cortex similarly to the cat V1. [ABSTRACT FROM AUTHOR]

This paper introduces a novel aerial building detection method based on region orientation as a new feature, which is used in various steps throughout the presented framework. As building objects are expected to be connected with each other on a regional level, exploiting the main orientation obtained from the local gradient analysis provides further information for detection purposes. The orientation information is applied for an improved edge map design, which is integrated with classical features like shadow and color. Moreover, an orthogonality check is introduced for finding building candidates, and their final shapes defined by the Chan–Vese active contour algorithm are refined based on the orientation information, resulting in smooth and accurate building outlines. The proposed framework is evaluated on multiple data sets, including aerial and high resolution optical satellite images, and compared to six state-of-the-art methods in both object and pixel level evaluation, proving the algorithm’s efficiency. [ABSTRACT FROM AUTHOR]

A common feature of the mammalian striate cortex is the arrangement of ‘orientation domains’ containing neurons preferring similar stimulus orientations. They are arranged as spokes of a pinwheel that converge at singularities known as ‘pinwheel centers’. We propose that a cortical network of feedforward and intracortical lateral connections elaborates a full set of optimum orientations from geniculate inputs that show a bias to stimulus orientation and form a set of two or a small number of ‘Cartesian’ coordinates. Because each geniculate afferent carries signals only from one eye and its receptive field (RF) is either ON or OFF center, the network constructs also ocular dominance columns and a quasi-segregation of ON and OFF responses across the horizontal extent of the striate cortex. [ABSTRACT FROM AUTHOR]

Using sinusoidal gratings we show that an increase in stimulus size confined to the dimension orthogonal to the axis of motion leads to stronger Ocular Following Responses (OFRs) up to a certain optimal size. An increase beyond this optimum produces smaller responses, indicating suppressive interactions. In sharp contrast, when the stimulus growth occurs parallel to the axis of motion OFR magnitudes increase monotonically both for horizontal and vertical directions of motion. Similar results are obtained with 1D white noise patterns. However, the OFR spatial anisotropy is minimal with 2D white noise patterns, revealing a pivotal role of orientation-selective (i.e., cortical) mechanisms in mediating this phenomenon. The lack of anisotropy for 2D patterns suggests that directional signals alone are not sufficient to elicit this suppression. The OFR spatial anisotropy is potentiated if a stationary grating is presented for 600–1000 ms before its motion commences, further emphasizing the importance of static orientation signals. These results suggest that the strength of cortical spatial interactions is asymmetric—i.e., larger in the direction of the ends than the flanks of an orientation-selective receptive field—which corroborates the existing neurophysiological evidence. [ABSTRACT FROM AUTHOR]

Highlights: [•] We studied responses of cat LGN neurons to large and high spatial frequency gratings. [•] More than 90% of LGN neurons exhibited significant orientation selectivity. [•] Both an elongated receptive field and surround suppression contributed to the selectivity. [•] The orientation tuning of LGN neurons showed a stimulus-contrast invariant property. [•] GABAA inhibition seemed to enhance the orientation selectivity in the LGN. [ABSTRACT FROM AUTHOR]

Highlights: [•] V1 cortical functions were investigated in morphine- and saline-treated cats. [•] Significant degradation of visual functions was found in morphine-treated cats. [•] In both groups, visual functions were improved by GABA but were degraded by BMI. [•] GABA application diminished the differences in visual functions between two groups. [ABSTRACT FROM AUTHOR]

Abstract: Theoretical considerations have led to the concept that the cerebral cortex is operating in a balanced state in which synaptic excitation is approximately balanced by synaptic inhibition from the local cortical circuit. This paper is about the functional consequences of the balanced state in sensory cortex. One consequence is gain control: there is experimental evidence and theoretical support for the idea that local circuit inhibition acts as a local automatic gain control throughout the cortex. Second, inhibition increases cortical feature selectivity: many studies of different sensory cortical areas have reported that suppressive mechanisms contribute to feature selectivity. Synaptic inhibition from the local microcircuit should be untuned (or broadly tuned) for stimulus features because of the microarchitecture of the cortical microcircuit. Untuned inhibition probably is the source of Untuned Suppression that enhances feature selectivity. We studied inhibition’s function in our experiments, guided by a neuronal network model, on orientation selectivity in the primary visual cortex, V1, of the Macaque monkey. Our results revealed that Untuned Suppression, generated by local circuit inhibition, is crucial for the generation of highly orientation-selective cells in V1 cortex. [Copyright &y& Elsevier]

Abstract: Optical imaging of intrinsic signals across the primary visual cortex in mammals has shown that neurons tuned to the same stimulus orientation are clustered together to form orientation domains, which converge on singularities called pinwheel centres. We used a combination of two gratings in different mutual relationships as in a plaid to study how visual cortical neurons differ in integrating these signals. Neurons in the centres of orientation domains responded to a smaller range of such composite stimuli than cells near pinwheel centres, even though orientation tuning for a single bar or grating did not differ significantly between the two locations. We believe that this difference between the two locations is related to the way local intracortical interactions generate a full complement of orientation preferences from a limited number of preferred stimulus orientations represented in the geniculate afferents to the striate cortex. [Copyright &y& Elsevier]

Abstract: In the monkey''s visual cortex, there are two well-documented information processing streams: the dorsal motion and ventral form/color pathways. Similarly, two corresponding information streams were also found in the cat''s visual cortices, and PMLS and area 21a are the gateways for distinct motion and form information processing. It has been shown that the feedback from PMLS solely modulates motion direction, but not orientation response, while the feedback from area 21a modulates form related features, such as spatial frequency dependency and neuronal oblique effect. Here, we postulate that feedback signals from higher cortical areas in the form or the motion information pathway may solely modulate the corresponding properties in neurons in the lower areas of the visual system. To examine the above hypothesis, the impact of feedback from higher area 21a on both orientation and direction maps was investigated in area 17 of the cat using intrinsic signal optical imaging. The results showed that the feedback from area 21a did not affect the amplitude and preference of direction, but did modulate orientation response in area 17, supporting the above hypothesis. [Copyright &y& Elsevier]

Abstract: We addressed how spatial frequency and orientation selectivity coexist and co-vary in Macaque primary visual cortex (V1) by simulating cortical layer 4Cα of V1 with a large-scale network model and then comparing the model’s behavior with a population of cells we recorded in layer 4Cα. We compared the distributions of orientation and spatial frequency selectivity, as well as the correlation between the two, in the model with what we observed in the 4Cα population. We found that (1) in the model, both spatial frequency and orientation selectivity of neuronal firing are greater and more diverse than the LGN inputs to model neurons; (2) orientation and spatial frequency selectivity co-vary in the model in a way very similar to what we observed in layer 4Cα neurons; (3) in the model, orientation and spatial frequency selectivity co-vary because of intra-cortical inhibition. The results suggest that cortical inhibition provides a common mechanism for selectivity in multiple dimensions. [ABSTRACT FROM AUTHOR]

Abstract: The surround suppression of the receptive field is important for basic visual information processing, such as orientation specificity. To date, the effects of aging on the strength of surround suppression are not clear. To address this issue, we carried out extracellular single-unit studies of the receptive field properties of cells in the primary visual cortex (area V1) in young and old rhesus (Macaca mulatta) monkeys. When presented with the oriented central stimulus, we found that cells in old animals showed reduced orientation and direction selectivity compared with those in young animals. When presented with the oriented central stimulus together with the optimal surround stimulus, more selective cells {orientation bias (OB) ≥0.1; a bias of 0.1 is significant at the P<0.005 level} in animals of both ages showed reduced orientation selectivity compared with the experiment that presented only the oriented central stimulus. When presented with the optimal central stimulus together with the oriented surround stimulus, cells in old animals showed reduced orientation and direction selectivity compared with young animals. Moreover, broadly tuned cells (OB<0.1) in old animals exhibited significantly reduced suppression indices that quantified the strength of the surround suppression of the receptive field, when compared with those in young animals. These results suggest that aging may seriously affect the surround suppression of the receptive field of V1 cells. Thus, the decreased strength of surround suppression of the receptive field may be one possible reason for the decreased stimulus selectivity of V1 cells previously found in the senescent brain. This work will contribute to an understanding of the physiological mechanisms mediating surround suppression of the receptive field. [Copyright &y& Elsevier]

Abstract: Area 21a, located on the cat''s lateral suprasylvian cortex, is considered as a higher-order cortical area. Little is known about its specific role in visual processing. In this study, the functional organization of area 21a was investigated by optical imaging of intrinsic signals and was compared to that of primary visual areas. We found a clear modular pattern for orientation selectivity in area 21a, with signal amplitude being four times lower than that in primary visual areas. There were no significant differences between the domains'' characteristics, nor the tuning bandwidth, in areas of the primary visual cortex (17 and 18) and 21a. This suggests that the basic cortical structure is independent of the hierarchical level or function of one area. A uniform representation of spatial frequency was found in areas 17 and 18, as well as in area 21a. The mean preferred spatial frequency in area 21a was 0.30 c/deg. In contrast to area 18, no direction maps were observed in area 21a whether drifting gratings or random dot kinematograms were used. This study supports the proposal that area 21a plays a pivotal role along the ventral processing stream and is mainly involved in form processing. [Copyright &y& Elsevier]

Abstract: In the adult brain, sensory cortical neurons undergo transient changes of their response properties following prolonged exposure to an appropriate stimulus (adaptation). In cat V1, orientation-selective cells shift their preferred orientation after being adapted to a non-preferred orientation. There are conflicting reports as to the direction of those shifts, towards (attractive) or away (repulsive) from the adapter. Moreover, the mechanisms underlying attractive shifts remain unexplained. In the present investigation we show that attractive shifts are the most frequent outcome of a 12 min adaptation. Overall, cells displaying selectivity for oblique orientations exhibit significantly larger shifts than cells tuned to cardinal orientations. In addition, cells selective to cardinal orientations had larger shift amplitudes when the absolute difference between the original preferred orientation and the adapting orientation increased. Conversely, cells tuned to oblique orientations exhibited larger shift amplitudes when this absolute orientation difference was narrower. Hence, neurons tuned to oblique contours appear to show more plasticity in response to small perturbations. Two different mechanisms appear to produce attractive and repulsive orientation shifts. Attractive shifts result from concurrent response depression on the non-adapted flank and selective response facilitation on the adapted flank of the orientation tuning curve. In contrast, repulsive shifts are caused solely by response depression on the adapted flank. We suggest that an early mechanism leads to repulsive shifts while attractive shifts engage a subsequent late facilitation. A potential role for attractive shifts may be improved stimulus discrimination around the adapting orientation. [Copyright &y& Elsevier]

Abstract: In typical binocular rivalry demonstrations, disparate images presented in corresponding locations to the two eyes are found to alternate perceptually over time. Alternation in perception can occur even if the images presented to the two eyes do not overlap, if they are sufficiently close in space. This implies a spatial spread in the interocular interaction. The current set of experiments explores how the luminance pattern of a target, in relation to a rivalrous suppressor, affects its susceptibility to suppression. It was found that the susceptibility to suppression of a target pattern was nonlinearly related to the amount of luminance variation along the target in the direction perpendicular to the suppressing stimulus. For instance, there was a strong effect of the orientation of the grating pattern within the target on the total time of suppression, with much more suppression for horizontal gratings than vertical gratings when suppressor bars were oriented vertically, regardless of the luminance pattern within the suppressors. Furthermore, it was shown that the inclusion of a spatial gap between the vertical suppressors and the central portion of the target does more than simply change the spatial relationships, it adds new figural information, such as vertically orientated edges in the targets, that modify the susceptibility to suppression of the target, thereby interfering with measurements of spatial interaction functions. All of the results are consistent with selectively suppressing stimulus information that would interfere with stereoscopic matching to aid the binocular fusion of disparate retinal images. [Copyright &y& Elsevier]

Abstract: Binocular disparities applied to large-field patterns elicit vergence eye movements at ultra-short latencies. We used the electromagnetic search coil technique to record the horizontal and vertical positions of both eyes while subjects briefly viewed (150ms) large patterns that were identical at the two eyes except for a difference in position (binocular disparity) that was varied in direction from trial to trial. For accurate alignment with the stimuli, the horizontal and vertical disparity vergence responses (HDVRs, VDVRs) should vary as the sine and cosine, respectively, of the direction of the disparity stimulus vector. In a first experiment, using random-dots patterns (RDs) with a binocular disparity of 0.2°, this was indeed the case. In a second experiment, using 1-D sine-wave gratings with a binocular phase difference (disparity) of 1/4-wavelength, it was not the case: HDVRs were maximal when the grating was vertical and showed little decrement until the grating was oriented more than ∼65° away from vertical, whereas VDVRs were maximal when the grating was horizontal and began to decrement roughly linearly when the grating was oriented away from the horizontal. We attribute these complex directional dependencies with gratings to the aperture problem, and the HDVR data strongly resemble the stereothresholds for 1-D gratings, which are minimal when the gratings are vertical and remain constant for orientations up to ∼80° away from the vertical when expressed as spatial phase disparities [Morgan, M. J., & Castet, E. (1997). The aperture problem in stereopsis. Vision Research, 37, 2737–2744.]. To explain this constancy of stereothresholds, Morgan and Castet (1997) postulated detectors sensitive to the phase disparity of the gratings seen by the two eyes (rather than their linear separation along some fixed axis, such as the horizontal). However, because (1) our VDVR data with gratings did not show this constancy and (2) the available evidence strongly suggests that there are no major differences in the disparity detectors mediating the initial HDVR and VDVR, we sought an alternative explanation for our data. We show that the dependence of the initial HDVR and VDVR on grating orientation can be successfully modeled by a bias in the number and/or efficacy of the detectors that favors horizontal disparities. [Copyright &y& Elsevier]

Abstract: Visual function declines with age. Using extracellular single-unit in vivo recordings, we compared the function of primary visual cortical (area 17) cells in young and old paralyzed, anesthetized cats. The results reveal that cortical neurons in old cats exhibit higher visually evoked responses, higher spontaneous activities, lower signal-to-noise ratios, and weaker orientation and direction selectivity than do cells in young adult cats. These findings are consistent with previously reported age related declines in cortical function in senescent macaque monkeys. Thus, similar declines in cortical function accompany old age in different mammalian species with well developed cortices. [Copyright &y& Elsevier]

Abstract: We evaluated orientation discrimination thresholds using an external noise paradigm. Stimuli were spatiotemporal Gaussian patches of 2D orientation noise band-pass filtered in Fourier domain. Orientation acuity was measured for various combinations of stimulus spatial bandwidth, spatial frequency, and size as a function of orientation bandwidths of the stimuli. Stimulus contrast was matched in multiples of detection threshold. Consistent with the idea that stimulus orientation bandwidth acts as a source of external noise, orientation discrimination thresholds increased monotonically in all conditions with stimulus bandwidth. To interpret these results quantitatively, we first fitted a variance summation model to the data and derived the internal orientation noise, relative sampling efficiency, and orientation tuning of the mechanism underlying orientation discrimination. Due to the equivocal biological nature of these parameters for orientation discrimination, we investigated, with a modeling approach, how neural detectors characterized by a broad orientation tuning may support orientation discrimination. We demonstrated using the ideal-observer theory that while linear models, based on either unimodal filtering or center-surround opponency, predict the monotonic relationship between orientation discrimination threshold and orientation noise, a nonlinear model incorporating a broadband divisive inhibition in the orientation domain is a better candidate due to its contrast invariance. This model, using broad and similar orientation tuning for its excitatory and inhibitory inputs, accounts for the acute orientation acuity of human vision and proves to be robust despite the variance found in natural stimuli. [Copyright &y& Elsevier]

Abstract: Chronic opiate exposure leads to maladaptive changes in brain function. In view of the localization of opiate receptors in mammalian visual system, chronic opiate exposure is likely to affect the visual responses properties of V1 neurons. Using in vivo single-unit recording, we here showed that chronic morphine treatment resulted in the functional abnormality of primary visual cortical cells. When compared with saline-treated (as control) cats, cortical neurons in morphine-treated cats exhibited higher spontaneous activity, lower signal-to-noise ratios and weaker orientation and direction selectivity. However, re-exposure with morphine could significantly improve the function of V1 neurons in morphine-treated cats. These findings demonstrated that chronic morphine treatment could significantly degrade the response properties of V1 neurons and may lead to a function dependence on morphine in visual cortical cells. [Copyright &y& Elsevier]

Abstract: This paper addresses the issue of curvature coding in the mammalian visual system. Considering the successful account of cortical neurons as detectors of features of visual stimuli like orientation and spatial frequency among others, we discuss the role of curvature in visual processes, review some previous investigations on curvature and present a possible biologically plausible model of curvature detection. This model requires only orientation selective neurons (simple cells) and short-range connections, both known and well-documented features of the mammalian primary visual cortex. The dependence of the model on different parameters is explored and discussed. [Copyright &y& Elsevier]

We have developed a vision system which emulates the orientation selective receptive fields of simple cells in the primary visual cortex. The system consists of a silicon retina and a Field Programmable Gate Array (FPGA). First, the image is filtered by the Laplacian–Gaussian-like receptive field of the silicon retina, and then it is transferred to the FPGA. The orientation selection chip selectively aggregates multiple pixels of the silicon retina, mimicking the feedforward model proposed by Hubel and Wiesel. The present system exhibits the orientation selectivity with even and odd-type responses. The design of the present chip is applicable to implement higher order cells in the primary visual cortex, such as the complex cell. [Copyright &y& Elsevier]

Aim of this work is to present simple models of orientation selectivity in the visual cortex, which do not require massive computational effort. Three different models are compared, in order to gain deeper insight into the structure of cortical circuits generating inhibitory signals.All models represent a single hypercolumn. They differ as to the arrangement of inhibitory connections: in the first (“antiphase inhibition model”) inhibition is in phase opposition with excitation, but with a similar orientation tuning; in the second (“in-phase inhibition model”), inhibition is in phase with excitation, but with larger orientation tuning. In these two models the orientation width of inhibition increases with contrast. Finally, a third model (“center-surround model”) assumes that inhibition comes from the same cells providing excitation, hence the inhibition tuning is contrast-independent.All models, with suitable values of the intracortical synapse parameters, are able to mimic experimental results in the literature. A few differences are evident between the “center-surround model” and the other two, especially as to the dependence of cortical cell response on spatial frequency. The models can represent practical tools to test hypotheses on the disposition of cortical synapses avoiding massive computational efforts. [Copyright &y& Elsevier]

A new model of contour extraction and perceptual grouping in the primary visual cortex is presented and discussed. It differs from previous models since it incorporates four main mechanisms, according to recent physiological data: a feed-forward input from the lateral geniculate nucleus, characterized by Gabor elongated receptive fields; an inhibitory feed-forward input, maximally oriented in the orthogonal direction of the target cell, which suppresses non-optimal stimuli and warrants contrast invariance; an excitatory cortical feedback, which respects co-axial and co-modularity criteria; and a long-range isotropic feedback inhibition. Model behavior has been tested on artificial images with contours of different curvatures, in the presence of considerable noise or in the presence of broken contours, and on a few real images. A sensitivity analysis has also been performed on the role of intracortical synapses.Results show that the model can extract correct contours within acceptable time from image presentation (30–40 ms). The feed-forward input plays a major role to set an initial correct bias for the subsequent feedback and to ensure contrast-invariance. Long-range inhibition is essential to suppress noise, but it may suppress small contours due to excessive competition with greater contours. Cortical excitation sharpens the initial bias and improves saliency of the contours.Model results support the idea that contour extraction is one the primary steps in the visual processing stream, and that local processing in V1 is able to solve this task even in difficult conditions, without the participation of higher visual centers. [Copyright &y& Elsevier]

Brain computation, in the early visual system, is often considered as a hierarchical process in which features extracted in a given sensory relay are not present in previous stages of integration. In particular, orientation preference and its fine tuning selectivity are functional properties shared by most cortical cells and they are not observed at the preceding geniculate stage. A classical problem is identifying the mechanisms and circuitry underlying these computations. Several organizational principles have been proposed, giving different weights to the feedforward thalamocortical drive or to intracortical recurrent architectures. Within this context, an important issue is whether intracortical inhibition is fundamental for the genesis of stimulus selectivity, or rather normalizes spike response tuning with respect to other features such as stimulus strength or contrast, without influencing the selectivity bias and preference expressed in the excitatory input alone. We review here experimental observations concerning the presence or absence of inhibitory input evoked by non-preferred orientation/directions. Intracellular current clamp and voltage clamp recordings are analyzed in the light of new methods allowing us (1) to increase the visibility of inhibitory input, and (2) to continuously measure the visually evoked dynamics of input conductances. We conclude that there exists a diversity of synaptic input combinations generating the same profile of spike-based orientation selectivity, and that this diversity most likely reflects anatomical non-homogeneities in input sampling provided by the local context of the columnar and lateral intracortical network in which the considered cortical cell is embedded. [Copyright &y& Elsevier]

Motivated by the possible existence of post-natal cortical plasticity, we analyze Miller''s (J. Neurosci. 14 (1994) 409–441) correlation-based plasticity dynamics using sinusoidal patterns of varying frequency and orientation. After demonstrating that this leads to the formation of a cluttered receptive field (RF), and analyzing the reasons therefor, we propose a Kohonen-type, response-dependent modulation of Miller''s dynamics. We analyze the simulation outputs—the RF profiles and preference maps—arising from changes in the model parameters. Further, in an attempt to quantify the hypothesis that (i) spontaneous activity and (ii) visual experience play prominent roles in the (a) establishment and (b) maturity of orientation selectivity, respectively, we initialize the plasticity dynamics with developing Miller-type RFs. We interpret such an initialization to form a combined pre-natal–post-natal model, and quantify the relative effects of spontaneous activity and visual experience on developing RFs and their preference organization. As a next step, we analyze a possible quantification of the critical period phenomenon in the proposed model, and discuss the biological implications of such a quantification. Further, we subject the model to selective rearing by presenting it with biased visual environments. By analyzing the results, and calibrating the output using its appropriate biological counterparts, we show that the model measures up to biological realities. We also fix bounds for certain model parameters by comparing the results with biological data. [Copyright &y& Elsevier]

We study the topographic development of visual receptive fields by simulating the continuum field equations with learning on a two-dimensional lattice. The observed plasticity reveals a columnar organization with spatial clustering of receptive field centers and the development of orientation selective neurons. [Copyright &y& Elsevier]

A large-scale computational model of the primate primary visual system was constructed using GENESIS. The model consists of ∼10 000 biologically plausible neurons organized into six arrays, which represent sectors of two retinas, two laminae of the dorsal lateral geniculate nucleus and two laminae of the visual cortex. The physiological and architectural properties of the model were derived from experimental data for the mammalian primary visual pathway. Neurons have shown ocular and orientation selectivity dependent responses in good agreement with data. [Copyright &y& Elsevier]

A new correlation-based model for ocular dominance and orientation selectivity columns is proposed. This model can be used to obtain realistic maps for either the ocular dominance maps or orientation selectivity maps. It can also be used to generate joint maps that take into account the extra requirements related to the singularities of the orientation selectivity map and the relative angles of intersection between the contour lines of the two maps. For future research we propose the use of stochastic processes in generating cortical maps and modification of Hebbian cortical interaction terms to make the model more biologically plausible. [Copyright &y& Elsevier]

Physiological studies have demonstrated a subcortical origin for orientation selectivity and the orientation columns of the primary visual cortex. However, there are no anatomical data showing how subcortical cells contribute to this important property. Optical imaging, combined with 1,1′-dioctadecyl-3,3,3,3′-tetramethylin-docarbocyanine perchlolate (DiI) and biocytin retrograde tracing, reveals that relay cells projecting to a single orientation column representing the horizontal meridian were clustered within 300 μm in the dorsal lateral geniculate nucleus (LGN). Interestingly, some labeled cells were located on a line parallel to an iso-elevation line in the LGN. Thus, according to the quantitative projection of the visual field to the LGN (J. Comp. Neurol. 143 (1971) 101), their receptive fields must distribute horizontally in alignment in the visual field providing the first anatomical evidence for Hubel and Wiesel''s model of simple cell receptive fields (J. Physiol. 160 (1962) 106). [Copyright &y& Elsevier]

Motion streaks are smeared representation of fast-moving objects due to temporal integration. Here, we test for motion streak signals in mice with two-photon calcium imaging. For small dots moving at low speeds, neurons in primary visual cortex (V1) encode the component motion, with preferred direction along the axis perpendicular to their preferred orientation. At high speeds, V1 neurons prefer the direction along the axis parallel to their preferred orientation, as expected for encoding motion streaks. Whereas some V1 neurons (∼20%) display a switch of preferred motion axis with increasing speed, others (>40%) respond specifically to high speeds at the parallel axis. Motion streak neurons are also seen in higher visual lateromedial (LM), anterolateral (AL), and rostrolateral (RL) areas, but with higher transition speeds, and many still prefer the perpendicular axis even with fast motion. Our results thus indicate that diverse motion encoding exists in mouse visual cortex, with intriguing differences among visual areas. • Many neurons in mouse V1 specifically encode motion streaks • Other streak neurons display a switch of motion axis with increasing stimulus speed • The speed at which axis switch occurs is different among visual areas • Many higher visual areal neurons still respond to perpendicular motion at high speeds Tohmi et al. report diverse motion processing in mouse visual cortex and intriguing differences among areas. Neurons that specifically encode motion streaks are found as early as in V1, and many neurons in higher visual areas still respond to component motion at high speeds. [ABSTRACT FROM AUTHOR]

We develop an effective blind image blur assessment model based on a novel orientation-aware local pattern operator. The resulting metric first proposes an orientation-aware local pattern operator that fully considers the impact of anisotropy of orientation selectivity mechanism and the gradient orientation effect on visual perception. Our results indicate that the proposed descriptor is sensitive to image distortion and can effectively represent orientation information. We thus use it to extract image structure information. In order to enhance features' representation capability for blur image, we extract edge information by a Toggle operator and use it as weight of local patterns to optimize the computed structural statistical features. Finally, a support vector regression method is used to train a predictive model with optimized features and subjective scores. Experimental results obtained on six public databases show that our proposed model performs better than state-of-the-art image blur assessment models. • An orientation-aware local pattern operator is proposed. • The proposed descriptor is deployed to extract image structure information. • Toggle operator is introduced to optimize image's statistical features. • The resulting image blur metric outperforms state-of-the art image blur assessment models. [ABSTRACT FROM AUTHOR]

This in vivo study shows that both intrinsic and sensory-evoked synaptic properties of layer 2/3 neurons in mouse visual cortex are modified by ongoing visual input. Following visual deprivation, intrinsic properties are significantly altered, although orientation selectivity across the population remains unchanged. We, therefore, suggest that cortical cells adjust their intrinsic excitability in an activity-dependent manner to compensate for changes in synaptic drive and maintain sensory network function. • Intrinsic properties of V1 L2/3 neurons are modulated by ongoing sensory input • Visually evoked synaptic responses are reduced after visual deprivation • Deprivation has little effect on spiking or subthreshold orientation selectivity • Cortical cells preserve sensory function despite long-term changes in synaptic drive This large-scale in vivo study by Brown et al. shows that the intrinsic and synaptic properties of V1 layer 2/3 neurons are modulated by ongoing visual input. However, despite significant changes in cellular intrinsic and synaptic properties after visual deprivation, overall functional selectivity for oriented stimuli remains unchanged. [ABSTRACT FROM AUTHOR]

The connectivity principles underlying the emergence of orientation selectivity in primary visual cortex (V1) of mammals lacking an orientation map (such as rodents and lagomorphs) are poorly understood. We present a computational model in which random connectivity gives rise to orientation selectivity that matches experimental observations. The model predicts that mouse V1 neurons should exhibit intricate receptive fields in the two-dimensional frequency domain, causing a shift in orientation preferences with spatial frequency. We find evidence for these features in mouse V1 using calcium imaging and intracellular whole-cell recordings. • Random connectivity explains orientation selectivity in visual cortex • Preferred orientation depends on spatial frequency Pattadkal et al. show that orientation selectivity can emerge from random connectivity, and offer a distinct perspective for how computations occur in the neocortex. They propose that a random convergence of inputs can provide signals for orientation preference in contrast with the dominant model that requires a precise arrangement. [ABSTRACT FROM AUTHOR]

Summary Sensory perception depends on interactions among cortical areas. These interactions are mediated by canonical patterns of connectivity in which higher areas send feedback projections to lower areas via neurons in superficial and deep layers. Here, we probed the circuit basis of interactions among two areas critical for touch perception in mice, whisker primary (wS1) and secondary (wS2) somatosensory cortices. Neurons in layer 4 of wS2 (S2 L4 ) formed a major feedback pathway to wS1. Feedback from wS2 to wS1 was organized somatotopically. Spikes evoked by whisker deflections occurred nearly as rapidly in wS2 as in wS1, including among putative S2 L4 → S1 feedback neurons. Axons from S2 L4 → S1 neurons sent stimulus orientation-specific activity to wS1. Optogenetic excitation of S2 L4 neurons modulated activity across both wS2 and wS1, while inhibition of S2 L4 reduced orientation tuning among wS1 neurons. Thus, a non-canonical feedback circuit, originating in layer 4 of S2, rapidly modulates early tactile processing. [ABSTRACT FROM AUTHOR]

An abstract of the article "The Generation of Receptive-Field Structure in Cat Primary Visual Cortex," by L. M. Martinez is presented.