Organization Of Visual Cortex Research Articles

Visuotopic Cortical Connectivity Underlying Attention Revealed with White-Matter Tractography

Visual attention selects behaviorally relevant information for detailed processing by resolving competition for representation among stimuli in retinotopically organized visual cortex. The signals that control this attentional biasing are thought to arise in a frontoparietal network of several brain regions, including posterior parietal cortex. Recent studies have revealed a topographic organization in the intraparietal sulcus (IPS) that mirrors the retinotopic organization in visual cortex, suggesting that connectivity between these regions might provide the mechanism by which attention acts on early cortical representations. Using white-matter imaging and functional MRI, we examined the connectivity between two topographic regions of IPS and six retinotopically defined areas in visual cortex. We observed a strong positive correlation between attention modulations in visual cortex and connectivity of posterior IPS, suggesting that these white-matter connections mediate the attention signals that resolve competition among stimuli for representation in visual cortex. Furthermore, we found that connectivity between IPS and V1 consistently respects visuotopic boundaries, whereas connections to V2 and V3/VP disperse by 60%. This pattern is consistent with changes in receptive field size across regions and suggests that a primary role of posterior IPS is to code spatially specific visual information. In summary, we have identified white-matter pathways that are ideally suited to carry attentional biasing signals in visuotopic coordinates from parietal control regions to sensory regions in humans. These results provide critical evidence for the biased competition theory of attention and specify neurobiological constraints on the functional brain organization of visual attention.

Orientation based saliency and visual search in the archer fish

Event Abstract Back to Event Orientation based saliency and visual search in the archer fish Alik Mokeichev1, 2*, Ronen Segev2, 3 and Ohad Ben-Shahar1, 2 1 Ben Gurion University of the Negev, Department of Computer Science, Israel 2 Ben Gurion University of the Negev, Zlotowski Center for Neuroscience, Israel 3 Ben-Gurion University of the Negev, Department of Life Sciences, Israel Orientations based visual saliency effects have been extensively demonstrated in behavioral experiments with humans and other primates, and in many theoretical models have been tightly linked to known properties of the anatomical and functional organization of early visual cortex. Employing a novel behavioral methodology in experiments with the archer fish, a proficient hunter with remarkable visual abilities (Schlegel and Schuster, 2008), we observed orientation saliency effects similar to those observed with human subject (Mokeichev, Segev and Ben-Shahar, 2010). Such findings challenge our current conceptions of the necessitous physiological hardware for processing orientations saliency. In other experiments with human subjects we exploited our unique methodological approach to find interactions between chromatic and achromatic mechanisms in processing of orientation saliency. These finding, again, challenge the general view of largely independent processing streams of chromatic and achromatic information at early stages of the visual pathways. We conjecture that both of these studies suggest orientation-based saliency processing to constitute a fundamental (and abstract) building block for efficient visual information processing. Acknowledgements This work was supported in part by the DFG and the Israel Science Foundation, as well as the Zlotowski Center for Neuroscience, the Paul Ivanier Robotics Center, the Frankel Fund at Ben-Gurion University. References Schlegel, T., and Schuster, S.(2008). Small circuits for large tasks: high-speed decision-making in archerfish. Science 319, 104-106 Mokeichev, A., Segev, R., and Ben-Shahar, O. (2010). Orientation saliency without visual cortex and target selection in archer fish. PNAS 107, 16726–16731. Keywords: archer fish, visual saliency, orientation saliency, visual search, orientation pop out, color pop out, visual information processing, orientation-based texture segregation Conference: Tenth International Congress of Neuroethology, College Park. Maryland USA, United States, 5 Aug - 10 Aug, 2012. Presentation Type: Invited Symposium (only for people who have been invited to a particular symposium) Topic: Sensory: Vision Citation: Mokeichev A, Segev R and Ben-Shahar O (2012). Orientation based saliency and visual search in the archer fish. Conference Abstract: Tenth International Congress of Neuroethology. doi: 10.3389/conf.fnbeh.2012.27.00069 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 04 Jul 2012; Published Online: 07 Jul 2012. * Correspondence: Mr. Alik Mokeichev, Ben Gurion University of the Negev, Department of Computer Science, Be'er Sheva, 84105, Israel, mokeiche@cs.bgu.ac.il Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Alik Mokeichev Ronen Segev Ohad Ben-Shahar Google Alik Mokeichev Ronen Segev Ohad Ben-Shahar Google Scholar Alik Mokeichev Ronen Segev Ohad Ben-Shahar PubMed Alik Mokeichev Ronen Segev Ohad Ben-Shahar Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Laminar circuit organization and response modulation in mouse visual cortex

The mouse has become an increasingly important animal model for visual system studies, but few studies have investigated local functional circuit organization of mouse visual cortex. Here we used our newly developed mapping technique combining laser scanning photostimulation (LSPS) with fast voltage-sensitive dye (VSD) imaging to examine the spatial organization and temporal dynamics of laminar circuit responses in living slice preparations of mouse primary visual cortex (V1). During experiments, LSPS using caged glutamate provided spatially restricted neuronal activation in a specific cortical layer, and evoked responses from the stimulated layer to its functionally connected regions were detected by VSD imaging. In this study, we first provided a detailed analysis of spatiotemporal activation patterns at specific V1 laminar locations and measured local circuit connectivity. Then we examined the role of cortical inhibition in the propagation of evoked cortical responses by comparing circuit activity patterns in control and in the presence of GABAa receptor antagonists. We found that GABAergic inhibition was critical in restricting layer-specific excitatory activity spread and maintaining topographical projections. In addition, we investigated how AMPA and NMDA receptors influenced cortical responses and found that blocking AMPA receptors abolished interlaminar functional projections, and the NMDA receptor activity was important in controlling visual cortical circuit excitability and modulating activity propagation. The NMDA receptor antagonist reduced neuronal population activity in time-dependent and laminar-specific manners. Finally, we used the quantitative information derived from the mapping experiments and presented computational modeling analysis of V1 circuit organization. Taken together, the present study has provided important new information about mouse V1 circuit organization and response modulation.

The case for primate V3

The visual system in primates is represented by a remarkably large expanse of the cerebral cortex. While more precise investigative studies that can be performed in non-human primates contribute towards understanding the organization of the human brain, there are several issues of visual cortex organization in monkey species that remain unresolved. In all, more than 20 areas comprise the primate visual cortex, yet there is little agreement as to the exact number, size and visual field representation of all but three. A case in point is the third visual area, V3. It is found relatively early in the visual system hierarchy, yet over the last 40 years its organization and even its very existence have been a matter of debate among prominent neuroscientists. In this review, we discuss a large body of recent work that provides straightforward evidence for the existence of V3. In light of this, we then re-examine results from several seminal reports and provide parsimonious re-interpretations in favour of V3. We conclude with analysis of human and monkey functional magnetic resonance imaging literature to make the case that a complete V3 is an organizational feature of all primate species and may play a greater role in the dorsal stream of visual processing.

Functional Specialization of Seven Mouse Visual Cortical Areas

To establish the mouse as a genetically tractable model for high-order visual processing, we characterized fine-scale retinotopic organization of visual cortex and determined functional specialization of layer 2/3 neuronal populations in seven retinotopically identified areas. Each area contains a distinct visuotopic representation and encodes a unique combination of spatiotemporal features. Areas LM, AL, RL, and AM prefer up to three times faster temporal frequencies and significantly lower spatial frequencies than V1, while V1 and PM prefer high spatial and low temporal frequencies. LI prefers both high spatial and temporal frequencies. All extrastriate areas except LI increase orientation selectivity compared to V1, and three areas are significantly more direction selective (AL, RL, and AM). Specific combinations of spatiotemporal representations further distinguish areas. These results reveal that mouse higher visual areas are functionally distinct, and separate groups of areas may be specialized for motion-related versus pattern-related computations, perhaps forming pathways analogous to dorsal and ventral streams in other species.

Closely overlapping responses to tools and hands in left lateral occipitotemporal cortex

The perception of object-directed actions performed by either hands or tools recruits regions in left fronto-parietal cortex. Here, using functional MRI (fMRI), we tested whether the common role of hands and tools in object manipulation is also reflected in the distribution of response patterns to these categories in visual cortex. In two experiments we found that static pictures of hands and tools activated closely overlapping regions in left lateral occipitotemporal cortex (LOTC). Left LOTC responses to tools selectively overlapped with responses to hands but not with responses to whole bodies, nonhand body parts, other objects, or visual motion. Multivoxel pattern analysis in left LOTC indicated a high degree of similarity between response patterns to hands and tools but not between hands or tools and other body parts. Finally, functional connectivity analysis showed that the left LOTC hand/tool region was selectively connected, relative to neighboring body-, motion-, and object-responsive regions, with regions in left intraparietal sulcus and left premotor cortex that have previously been implicated in hand/tool action-related processing. Taken together, these results suggest that action-related object properties shared by hands and tools are reflected in the organization of high-order visual cortex. We propose that the functional organization of high-order visual cortex partly reflects the organization of downstream functional networks, such as the fronto-parietal action network, due to differences within visual cortex in the connectivity to these networks.

Closely overlapping responses to tools and hands in the left lateral occipitotemporal cortex

Tools and hands are functionally related through their common role in action. In two fMRI studies we show that this functional relationship is reflected in the spatial distribution of hand- and tool-selective responses in the higher-level visual cortex. Results from Study 1 (N = 15) showed that the processing of tools and hands (relative to mammals and scenes) recruited overlapping regions in left lateral occipitotemporal cortex (LOTC). This overlap was unlikely to be related to shared implied motion or general object processing properties, since motion-selective regions (hMT) and object-selective regions (LO) were located posterior to the tool-hand cluster, and did not respond selectively to either hands or tools. Study 2 (N = 15) investigated whether the tool-hand overlap in left LOTC is specific to hands or generalizes to other body parts. Individual-subject region-of-interest analysis showed that tool-selective responses were more closely overlapping with hand-selective responses (80% overlap) than they were with non-hand body-part selective responses (38% overlap). Moreover, multi-voxel pattern analysis in left LOTC indicated a surprising degree of similarity between multi-voxel response patterns to tools and hands, but not between tools and other body parts. Together, these results indicate that tools and hands are represented in closely overlapping left occipitotemporal regions, despite differences in visual appearance and animacy. We propose that the functional organization of higher-level visual cortex is partly determined by the type of information that objects provide and specific network connectivity constraints: form-related object representations have to interact with those brain regions that specify the functional role of the objects (e.g. the left-lateralized fronto-parietal action network).

A biological plausible recurrent model of V1 hypercolumns

A biological plausible model of hypercolumn of V1 layer in the Primary Visual Cortex, modeled in the NEST Environment [1], is presented. The model addresses experimental findings on emergence of orientation selectivity which occurs in the V1 [2]. The network model is derived from the Bayesian confidence propagation neural network, which was presented earlier [3,4]. It is hypothesized that a modular recurrent network model can be used to address orientation selectivity mechanism [2]. Thus, the columnar organization of primary visual cortex is assumed [5]. The network consists of 16 minicolumn models each representing an orientation, ranging from 0o to 168.75o, with the angular distance of 11.25o between two adjacent minicolumn models. LGN input is broadly tuned, half-width of half-height (HWHH) is 40 o. Excitatory->Excitatory network targets all neurons with the probability of 60% inside the host minicolumn with a HWHH of 25o as a function of distance (ESPSs = 3.15 mV). Inhibitory->Excitatory is connected with the probability of 40% (ISPSs = -5.85mV). Excitatory->Inhibitory connections target all neurons with the probability of 40%, and HWHH of 67.5o as a function of distance (ESPSs = 1.35 mV). Furthermore, LGN input is 1/3 of cortical excitation. Hypercolumn model also reflects biological phenomenon of background activity caused by random cortical inputs, as suggested by the experimental findings. In the absence of LGN input, background activity of the population is around 0.5-2 spikes/sec.

The Functional Neuroanatomy of Object Agnosia: A Case Study

Cortical reorganization of visual and object representations following neural injury was examined using fMRI and behavioral investigations. We probed the visual responsivity of the ventral visual cortex of an agnosic patient who was impaired at object recognition following a lesion to the right lateral fusiform gyrus. In both hemispheres, retinotopic mapping revealed typical topographic organization and visual activation of early visual cortex. However, visual responses, object-related, and -selective responses were reduced in regions immediately surrounding the lesion in the right hemisphere, and also, surprisingly, in corresponding locations in the structurally intact left hemisphere. In contrast, hV4 of the right hemisphere showed expanded response properties. These findings indicate that the right lateral fusiform gyrus is critically involved in object recognition and that an impairment to this region has widespread consequences for remote parts of cortex. Finally, functional neural plasticity is possible even when a cortical lesion is sustained in adulthood.

Not one extrastriate body area: Using anatomical landmarks, hMT+, and visual field maps to parcellate limb-selective activations in human lateral occipitotemporal cortex

The prevailing view of human lateral occipitotemporal cortex (LOTC) organization suggests a single area selective for images of the human body (extrastriate body area, EBA) that highly overlaps with the human motion-selective complex (hMT+). Using functional magnetic resonance imaging with higher resolution (1.5mm voxels) than past studies (3–4mm voxels), we examined the fine-scale spatial organization of these activations relative to each other, as well as to visual field maps in LOTC. Rather than one contiguous EBA highly overlapping hMT+, results indicate three limb-selective activations organized in a crescent surrounding hMT+: (1) an activation posterior to hMT+ on the lateral occipital sulcus/middle occipital gyrus (LOS/MOG) overlapping the lower vertical meridian shared between visual field maps LO-2 and TO-1, (2) an activation anterior to hMT+ on the middle temporal gyrus (MTG) consistently overlapping the lower vertical meridian of TO-2 and extending outside presently defined visual field maps, and (3) an activation inferior to hMT+ on the inferotemporal gyrus (ITG) overlapping the parafoveal representation of the TO cluster. This crescent organization of limb-selective activations surrounding hMT+ is reproducible over a span of three years and is consistent across different image types used for localization. Further, these regions exhibit differential position properties: preference for contralateral image presentation decreases and preference for foveal presentation increases from the limb-selective LOS to the MTG. Finally, the relationship between limb-selective activations and visual field maps extends to the dorsal stream where a posterior IPS activation overlaps V7. Overall, our measurements demonstrate a series of LOTC limb-selective activations that 1) have separate anatomical and functional boundaries, 2) overlap distinct visual field maps, and 3) illustrate differential position properties. These findings indicate that category selectivity alone is an insufficient organization principle for defining brain areas. Instead, multiple properties are necessary in order to parcellate and understand the functional organization of high-level visual cortex.

Multiple scales of organization for object selectivity in ventral visual cortex

Object knowledge is hierarchical. Several hypotheses have proposed that this property might be reflected in the spatial organization of ventral visual cortex. For example, all exemplars of a category might activate the same patches of cortex, but with a slightly different position of the peak of activation in each patch. According to this view, category selectivity would be organized at a larger spatial scale compared to exemplar selectivity. No empirical evidence for such proposals is available from experiments with human subjects. Here, we compare the relative scale of organization for category and exemplar selectivity in two datasets with two methods: (i) by investigating the previously reported beneficial effect of spatial smoothing of the fMRI data on the reliability of multi-voxel selectivity patterns; and (ii) by comparing the relative weight of lower and higher spatial frequencies in the spatial frequency spectrum of these selectivity patterns. The findings are consistent with the proposal that selectivity for stimulus properties that underlie finer distinctions between objects is organized at a finer scale than selectivity for stimulus properties that differentiate categories. This finding confirms the existence of multiple scales of organization in the ventral visual pathway.

A Motion Direction Map in Macaque V2

In mammals, the perception of motion starts with direction-selective neurons in the visual cortex. Despite numerous studies in monkey primary and second visual cortex (V1 and V2), there has been no evidence of direction maps in these areas. In the present study, we used optical imaging methods to study the organization of motion response in macaque V1 and V2. In contrast to the findings in other mammals (e.g., cats and ferrets), we found no direction maps in macaque V1. Robust direction maps, however, were found in V2 thick/pale stripes and avoided thin stripes. In many cases direction maps were located within thick stripes and exhibited pinwheel or linear organizations. The presence of motion maps in V2 points to a newfound prominence of V2 in motion processing, for contributing to motion perception in the dorsal pathway and/or for motion cue-dependent form perception in the ventral pathway.

Feature priming and the capture of visual attention: Linking two ambiguity resolution hypotheses

Visual search for a unique stimulus is often faster when the feature defining this target is repeated. Recent research has related this feature priming to ambiguity: priming effects appear stronger when the search target is perceptually ambiguous, as when the search array contains a salient distractor. Here we link the ambiguity that underlies feature priming to ambiguity in neural representation caused by the receptive field organization of visual cortex. We show that as the magnitude of neural activity involved in resolving perceptual ambiguity in early stages of visual cortex increases–indexed in posterior aspects of the N2pc component of the visual-event related potential–so does the behavioral feature priming effect. When ambiguity resolution mechanisms act strongly and the target repeats, target processing is facilitated. When these mechanisms act strongly, but the features that have previously defined the target come to characterize the distractor, attention is captured to the distractor location. These results suggest that ambiguity and the attentional mechanisms responsible for resolving it play central roles in feature priming.

Visuotopic organization of bush baby primary visual cortex (V1) revealed by optical imaging

Visuotopic organization of bush baby primary visual cortex (V1) revealed by optical imaging

Mapping Human Somatosensory Cortex in Individual Subjects With 7T Functional MRI

Functional magnetic resonance imaging (fMRI) is now routinely used to map the topographic organization of human visual cortex. Mapping the detailed topography of somatosensory cortex, however, has proven to be more difficult. Here we used the increased blood-oxygen-level-dependent contrast-to-noise ratio at ultra-high field (7 Tesla) to measure the topographic representation of the digits in human somatosensory cortex at 1 mm isotropic resolution in individual subjects. A "traveling wave" paradigm was used to locate regions of cortex responding to periodic tactile stimulation of each distal phalangeal digit. Tactile stimulation was applied sequentially to each digit of the left hand from thumb to little finger (and in the reverse order). In all subjects, we found an orderly map of the digits on the posterior bank of the central sulcus (postcentral gyrus). Additionally, we measured event-related responses to brief stimuli for comparison with the topographic mapping data and related the fMRI responses to anatomical images obtained with an inversion-recovery sequence. Our results have important implications for the study of human somatosensory cortex and underscore the practical utility of ultra-high field functional imaging with 1 mm isotropic resolution for neuroscience experiments. First, topographic mapping of somatosensory cortex can be achieved in 20 min, allowing time for further experiments in the same session. Second, the maps are of sufficiently high resolution to resolve the representations of all five digits and third, the measurements are robust and can be made in an individual subject. These combined advantages will allow somatotopic fMRI to be used to measure the representation of digits in patients undergoing rehabilitation or plastic changes after peripheral nerve damage as well as tracking changes in normal subjects undergoing perceptual learning.

Continuous mapping of the cortical object vision pathway using traveling waves in object space

Research into the organization of high-level visual cortex has mainly used discrete object classes (e.g. faces and buildings). In contrast, the lower levels of the visual cortex have mainly been studied using phase-encoding techniques with gradually changing rotating wedges and expanding/contracting rings. The gradual stimulus changes cause traveling waves on the cortical surface and time delays of each cortical location are related to stimulus preference. We propose to extend this method to study higher-order properties of visual objects. We created gradual morphing sequences from a face into a building and vice versa. The activation in traditional face- and house-selective regions corresponding to fusiform face area (FFA) and parahippocampal place area (PPA) was time-locked to presentation of respectively face(-like) and building(-like) stimuli in the morphing sequences. We also included contracting/expanding rings containing images of parts of natural scenes. Confirming existing literature with discrete object classes, activity in FFA and PPA was time-locked to the presentation of foveal and eccentric rings, respectively. The results however contradict large-scale continuous maps across the ventral visual stream, as the cortical area between FFA and PPA was not modulated by the position in the morphing sequences, or by the retinotopic position of the rings. We conclude that phase-encoding techniques can help in revealing the organization of high-level visual regions for complex object properties.

A Nonvisual Look at the Functional Organization of Visual Cortex

In this issue of Neuron, Mahon et al. show that the ventral visual cortex of congenitally blind individuals, who have never experienced the visual world, has an object-category organization similar to that found in sighted individuals. Here, we discuss the implications of this finding for our understanding of the "visual" cortex.

Advances in high-resolution imaging and computational unfolding of the human hippocampus

The hippocampus is often a difficult structure to visualize with magnetic resonance imaging (MRI) and functional MRI (fMRI) due to its convoluted nature and susceptibility to signal dropout. Improving our ability to pinpoint changes in neural activity using fMRI in this structure remains an important challenge. Current fMRI/MRI methods typically do not permit visualization of the hippocampus and surrounding cortex at a resolution less than 1 mm. We present here improvements to our previous methods for obtaining structural MR images of the hippocampus, which provided an in-plane resolution of 0.4 mm2 mm and two-dimensional “flat” maps of the hippocampus with an interpolated isotropic resolution of 0.4 mm3 (Engel, S.A., Glover, G.H., and Wandell, B.A., (1997). Retinotopic organization in human visual cortex and the spatial precision of functional MRI. Cereb. Cortex 7, 181–192.; Zeineh, M.M., Engel, S.A., and Bookheimer, S.Y., (2000). Application of cortical unfolding techniques to functional MRI of the human hippocampal region. NeuroImage 11, 668–683.). We present changes to existing structural imaging sequences that now augment the resolution of previous scans, permitting visualization of the anterior portion of CA1, parts of the dentate gyrus, and CA23. These imaging improvements are of relevance generally to the field of imaging because they permit higher overall resolution imaging of the hippocampus than previously possible (at 3 T). We also introduce a novel application of a computational interpolation method that improves our ability to capture the convoluted three-dimensional shape of the hippocampus. Furthermore, we have developed a quantitative method for obtaining group activation patterns based on producing averaged flat maps using vector field warping techniques, allowing localization of activations to specific hippocampal subregions across groups of subjects. Together, these methods provide a means to improve imaging of neural activity in the human hippocampus and surrounding cortex during cognitive tasks.

What are the effects of severe visual impairment on the cortical organization and connectivity of primary visual cortex?

The organization and connections of the primary visual area (V1) were examined in mice that lacked functional rods (Gnat−/−), but had normal cone function. Because mice are nocturnal and rely almost exclusively on rod vision for normal behaviors, the Gnat−/− mice used in the present study are considered functionally blind. Our goal was to determine if visual cortex is reorganized in these mice, and to examine the neuroanatomical connections that may subserve reorganization. We found that most neurons in V1 responded to auditory, or some combination of auditory, somatosensory, and/or visual stimulation. We also determined that cortical connections of V1 in Gnat−/− mice were similar to those in normal animals, but even in normal animals, there is sparse input from auditory cortex (AC) to V1. An important observation was that most of the subcortical inputs to V1 were from thalamic nuclei that normally project to V1 such as the lateral geniculate (LG), lateral posterior (LP), and lateral dorsal (LD) nuclei. However, V1 also received some abnormal subcortical inputs from the anterior thalamic nuclei, the ventral posterior, the ventral lateral and the posterior nuclei. While the vision generated from the small number of cones appears to be sufficient to maintain most of the patterns of normal connectivity, the sparse abnormal thalamic inputs to VI, existing inputs from AC, and possibly abnormal inputs to LG and LP may be responsible for generating the alterations in the functional organization of V1.

A Map for Horizontal Disparity in Monkey V2

The perception of visual depth is determined by integration of spatial disparities of inputs from the two eyes. Single cells in visual cortex of monkeys are known to respond to specific binocular disparities; however, little is known about their functional organization. We now show, using intrinsic signal optical imaging and single-unit physiology, that, in the thick stripe compartments of the second visual area (V2), there is a clustered organization of Near cells and Far cells, and moreover, there are topographic maps for Near to Far disparities within V2. Our findings suggest that maps for visual disparity are calculated in V2, and demonstrate parallels in functional organization between the thin, pale, and thick stripes of V2.