The Experts below are selected from a list of 31017 Experts worldwide ranked by ideXlab platform
Dario L. Ringach - One of the best experts on this subject based on the ideXlab platform.
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Spatial clustering of tuning in mouse Primary Visual Cortex.
Nature communications, 2016Co-Authors: Dario L. Ringach, Patrick J. Mineault, Elaine Tring, Nicholas D. Olivas, Pablo Garcia-junco-clemente, Joshua T. TrachtenbergAbstract:The preference of cells in mouse Primary Visual Cortex are thought to be randomly distributed in a salt-and-pepper map, in contrast to the smooth cortical maps observed in higher mammals. Here the authors show that excitatory cells in mouse Primary Visual Cortex are spatially clustered, resembling a degraded version of the organization seen in higher mammals.
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Link between orientation and retinotopic maps in Primary Visual Cortex
Proceedings of the National Academy of Sciences of the United States of America, 2012Co-Authors: Se-bum Paik, Dario L. RingachAbstract:Maps representing the preference of neurons for the location and orientation of a stimulus on the Visual field are a hallmark of Primary Visual Cortex. It is not yet known how these maps develop and what function they play in Visual processing. One hypothesis postulates that orientation maps are initially seeded by the spatial interference of ON- and OFF-center retinal receptive field mosaics. Here we show that such a mechanism predicts a link between the layout of orientation preferences around singularities of different signs and the cardinal axes of the retinotopic map. Moreover, we confirm the predicted relationship holds in tree shrew Primary Visual Cortex. These findings provide additional support for the notion that spatially structured input from the retina may provide a blueprint for the early development of cortical maps and receptive fields. More broadly, it raises the possibility that spatially structured input from the periphery may shape the organization of Primary sensory Cortex of other modalities as well.
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Dynamics of receptive field size in Primary Visual Cortex.
Journal of neurophysiology, 2006Co-Authors: Brian J. Malone, Vikas R. Kumar, Dario L. RingachAbstract:Recent studies have shown that the initial responses evoked by a stimulus in neurons of Primary Visual Cortex are dominated by low spatial frequency information in the image, whereas finer spatial scales dominate later in the response. Such phenomena could arise from the dynamics of receptive field (RF) size at early stages of cortical processing. We measured changes in RF size in simple cells recorded from the Primary Visual Cortex of anesthetized macaques by measuring their first-order spatio-temporal kernels and fitting them with two-dimensional Gabor functions at different time slices. We found that the width and length of the RF envelope and the period of the carrier tend to decrease during the time-course of the response. The most pronounced changes are seen in the width and spatial period of the RFs, which decrease by 15% during the central 20 ms of the response. These results show a novel form of spatio-temporal inseparability in simple cells and are consistent with the notion of a coarse-to-fine processing of information in early Visual Cortex.
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Spatial structure and symmetry of simple-cell receptive fields in macaque Primary Visual Cortex.
Journal of neurophysiology, 2002Co-Authors: Dario L. RingachAbstract:I present measurements of the spatial structure of simple-cell receptive fields in macaque Primary Visual Cortex (area V1). Similar to previous findings in cat area 17, the spatial profile of simple-cell receptive fields in the macaque is well described by two-dimensional Gabor functions. A population analysis reveals that the distribution of spatial profiles in Primary Visual Cortex lies approximately on a one-parameter family of filter shapes. Surprisingly, the receptive fields cluster into even- and odd-symmetry classes with a tendency for neurons that are well tuned in orientation and spatial frequency to have odd-symmetric receptive fields. The filter shapes predicted by two recent theories of simple-cell receptive field function, independent component analysis and sparse coding, are compared with the data. Both theories predict receptive fields with a larger number of subfields than observed in the experimental data. In addition, these theories do not generate receptive fields that are broadly tuned in orientation and low-pass in spatial frequency, which are commonly seen in monkey V1. The implications of these results for our understanding of image coding and representation in Primary Visual Cortex are discussed.
Stephen G. Lomber - One of the best experts on this subject based on the ideXlab platform.
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Auditory Cortex projections target the peripheral field representation of Primary Visual Cortex
Experimental Brain Research, 2008Co-Authors: Amee J. Hall, Stephen G. LomberAbstract:The purpose of the present study was to identify projections from auditory to Visual Cortex and their organization. Retrograde tracers were used to identify the sources of auditory cortical projections to Primary Visual Cortex (areas 17 and 18) in adult cats. Two groups of animals were studied. In the first group, large deposits were centered on the lower Visual field representation of the vertical meridian located along the area 17 and 18 border. Following tissue processing, characteristic patterns of cell body labeling were identified in extrastriate Visual Cortex and the Visual thalamus (LGN, MIN, & LPl). In auditory Cortex, of the four tonotopically-organized regions, neuronal labeling was identified in the supragranular layers of the posterior auditory field (PAF). Little to no labeling was evident in the Primary auditory Cortex, the anterior auditory field, the ventral posterior auditory field or in the remaining six non-tonotopically organized regions of auditory Cortex. In the second group, small deposits were made into the central or peripheral Visual field representations of Primary Visual Cortex. Labeled cells were identified in PAF following deposits into regions of Primary Visual Cortex representing peripheral, but not central, Visual field representations. Furthermore, a coarse topography was identified in PAF, with neurons projecting to the upper field representation being located in the gyral portion of PAF and neurons projecting to the lower field representation located in the sulcal portion of PAF. Therefore, direct projections can be identified from tonotopically organized auditory Cortex to the earliest stages of Visual cortical processing.
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Functional impact of Primary Visual Cortex deactivation on subcortical target structures in the thalamus and midbrain.
The Journal of comparative neurology, 2005Co-Authors: R. Jarrett Rushmore, Bertram R. Payne, Stephen G. LomberAbstract:The functional relationships between the Primary Visual Cortex and its major subcortical target structures have long been a subject of interest. We studied these relationships by using localized cooling deactivation to silence portions of Primary Visual Cortex and measuring 2-deoxyglucose (2DG) uptake to assess neural activity in subcortical and midbrain targets. We focused analysis on the largest subcortical targets of Primary Visual Cortex: the superior colliculus (SC), the dorsal lateral geniculate nucleus of the thalamus (dLGN), and the lateral division of the lateral posterior nucleus of the thalamus (LPL). We found that localized cooling of different regions of Primary Visual Cortex caused specific decreases in 2DG uptake in target structures such that the location of 2DG decrease varied according to joint retinotopy, and the magnitude of the decreases in target structures was associated with the amount of cooled Cortex. In addition, we found that the impact of cortical cooling was more profound on the SC than on the dLGN. The functional impact of cortical deactivations on the LPL was weak for small deactivations but approximated the impact on the SC when deactivations were large. We discuss these findings in terms of neural circuits and in terms of drivers and modulators. J. Comp. Neurol. 488:414–426, 2005. © 2005 Wiley-Liss, Inc.
Charles D Gilbert - One of the best experts on this subject based on the ideXlab platform.
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contour saliency in Primary Visual Cortex
Neuron, 2006Co-Authors: Valentin Piech, Charles D GilbertAbstract:Contour integration is an important intermediate stage of object recognition, in which line segments belonging to an object boundary are perceptually linked and segmented from complex backgrounds. Contextual influences observed in Primary Visual Cortex (V1) suggest the involvement of V1 in contour integration. Here, we provide direct evidence that, in monkeys performing a contour detection task, there was a close correlation between the responses of V1 neurons and the perceptual saliency of contours. Receiver operating characteristic analysis showed that single neuronal responses encode the presence or absence of a contour as reliably as the animal's behavioral responses. We also show that the same Visual contours elicited significantly weaker neuronal responses when they were not detected in the detection task, or when they were unattended. Our results demonstrate that contextual interactions in V1 play a pivotal role in contour integration and saliency.
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Spatial distribution of contextual interactions in Primary Visual Cortex and in Visual perception.
Journal of neurophysiology, 2000Co-Authors: Mitesh K. Kapadia, Gerald Westheimer, Charles D GilbertAbstract:To examine the role of Primary Visual Cortex in visuospatial integration, we studied the spatial arrangement of contextual interactions in the response properties of neurons in Primary Visual Cortex of alert monkeys and in human perception. We found a spatial segregation of opposing contextual interactions. At the level of cortical neurons, excitatory interactions were located along the ends of receptive fields, while inhibitory interactions were strongest along the orthogonal axis. Parallel psychophysical studies in human observers showed opposing contextual interactions surrounding a target line with a similar spatial distribution. The results suggest that V1 neurons can participate in multiple perceptual processes via spatially segregated and functionally distinct components of their receptive fields.
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Attention and Primary Visual Cortex
Proceedings of the National Academy of Sciences of the United States of America, 1999Co-Authors: Michael I Posner, Charles D GilbertAbstract:Evidence for attentional modulation of responses in Primary Visual Cortex has been a matter of considerable debate. The classical notion concerning attention effects in Visual Cortex has held that the strongest effects are seen at the highest levels of the Visual pathway, and that in Primary Visual Cortex there is no effect of attention. The report by Somers et al. (1) of a functional MRI study indicating Primary Visual Cortex (V1) modulation by instructions to attend illustrates the change that has taken place in recent years. This commentary expands on that theme by providing some of the history of work related to attention and V1 and by citing new studies of V1 modulation that use a variety of methods.
Michael A Paradiso - One of the best experts on this subject based on the ideXlab platform.
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Perceptual and neuronal correspondence in Primary Visual Cortex.
Current Opinion in Neurobiology, 2002Co-Authors: Michael A ParadisoAbstract:Recent findings from the study of Primary Visual Cortex in humans and animals blur the distinction between early and late Visual processing. Under some conditions, the activity of neurons in Primary Visual Cortex appears as close or closer to perception than activity in 'higher' Visual areas.
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Lightness constancy in Primary Visual Cortex
Proceedings of the National Academy of Sciences of the United States of America, 2001Co-Authors: Sean P. Macevoy, Michael A ParadisoAbstract:When the illumination of a Visual scene changes, the quantity of light reflected from objects is altered. Despite this, the perceived lightness of the objects generally remains constant. This perceptual lightness constancy is thought to be important behaviorally for object recognition. Here we show that interactions from outside the classical receptive fields of neurons in Primary Visual Cortex modulate neural responses in a way that makes them immune to changes in illumination, as is perception. This finding is consistent with the hypothesis that the responses of neurons in Primary Visual Cortex carry information about surface lightness in addition to information about form. It also suggests that lightness constancy, which is sometimes thought to involve “higher-level” processes, is manifest at the first stage of Visual cortical processing.
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Integration of surface information in Primary Visual Cortex.
Nature neuroscience, 1998Co-Authors: Sean P. Macevoy, Woojin Kim, Michael A ParadisoAbstract:Ample evidence suggests that Primary Visual Cortex is involved in the perception of form, and there is increasing evidence that it may also be important in the perception of surfaces. Perceptual qualities of surfaces, such as brightness, are based on extensive integration of information throughout the Visual field. In Primary Visual Cortex, we found that the responses of neurons to surfaces were also influenced by the intensity and organization of light in large portions of the Visual field. Interactions with surrounding stimuli typically extended 10 to 20 degrees beyond a cell's receptive field, the same spatial scale as perceptual interactions. Moreover, there were both facilitatory and inhibitory influences, just as there are additive and subtractive perceptual interactions. Surprisingly, influences from outside the receptive field obtained with surface stimuli did not reliably correlate with influences recorded with gratings. These properties suggest that the underlying neuronal interactions may serve as the fundamental building blocks of surface perception.
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The Representation of Brightness in Primary Visual Cortex
Science, 1996Co-Authors: Andrew F Rossi, Chadwick D. Rittenhouse, Michael A ParadisoAbstract:Although neurons in Primary Visual Cortex are sensitive to the spatial distribution and intensity of light, their responses have not been thought to correlate with the perception of brightness. Indeed, Primary Visual Cortex is often described as an initial processing stage that sends information to higher cortical areas where perception of brightness, color, and form occurs. However, a significant percentage of neurons in Primary Visual Cortex were shown to respond in a manner correlated with perceived brightness, rather than responding strictly to the light level in the receptive fields of the cells. This finding suggests that even at the first stage of Visual cortical processing, spatial integration of information yields perceptual qualities that are only indirectly related to the pattern of illumination of the retina.
Gilles Bronchti - One of the best experts on this subject based on the ideXlab platform.
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Cortical and subcortical projections to Primary Visual Cortex in anophthalmic, enucleated and sighted mice.
The European journal of neuroscience, 2012Co-Authors: Valérie Charbonneau, Marie-eve Laramée, Gilles Bronchti, Virginie Boucher, Denis BoireAbstract:The purpose of this study was to identify and compare the afferent projections to the Primary Visual Cortex in intact and enucleated C57BL/6 mice and in ZRDCT/An anophthalmic mice. Early loss of sensory-driven activity in blind subjects can lead to activations of the Primary Visual Cortex by haptic or auditory stimuli. This intermodal activation following the onset of blindness is believed to arise through either unmasking of already present cortical connections, sprouting of novel cortical connections or enhancement of intermodal cortical connections. Studies in humans have similarly demonstrated heteromodal activation of Visual Cortex following relatively short periods of blindfolding. This suggests that the Primary Visual Cortex in normal sighted subjects receives afferents, either from multisensory association cortices or from Primary sensory cortices dedicated to other modalities. Here cortical afferents to the Primary Visual Cortex were investigated to determine whether the Visual Cortex receives sensory input from other modalities, and whether differences exist in the quantity and/or the structure of projections found in sighted, enucleated and anophthalmic mice. This study demonstrates extensive direct connections between the Primary Visual Cortex and auditory and somatosensory areas, as well as with motor and association cortices in all three animal groups. This suggests that information from different sensory modalities can be integrated at early cortical stages and that Visual Cortex activations following Visual deprivations can partly be explained by already present intermodal corticocortical connections.
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Subcortical auditory input to the Primary Visual Cortex in anophthalmic mice.
Neuroscience letters, 2008Co-Authors: Nicole Chabot, Valérie Charbonneau, Marie-eve Laramée, R. Tremblay, Denis Boire, Gilles BronchtiAbstract:Anatomical and imaging studies show ample evidence for auditory activation of the Visual Cortex following early onset of blindness in both humans and animal models. Anatomical studies in animal models of early blindness clearly show intermodal pathways through which auditory information can reach the Primary Visual Cortex. There is clear evidence for intermodal corticocortical pathways linking auditory and Visual Cortex and also novel connections between the inferior colliculus and the Visual thalamus. A recent publication [L.K. Laemle, N.L. Strominger, D.O. Carpenter, Cross-modal innervation of Primary Visual Cortex by auditory fibers in congenitally anophthalmic mice, Neurosci. Lett. 396 (2006) 108-112] suggested the presence of a direct reciprocal connection between the inferior colliculus and the Primary Visual Cortex (V1) in congenitally anophthalmic ZRDCT/An mice. This implies that this mutant mouse would be the only known vertebrate having a direct tectal connection with a Primary sensory Cortex. The presence of this peculiar pathway was reinvestigated in the ZRDCT/An mouse with highly sensitive neuronal tracers. We found the connections normally described in the ZRDCT/An mouse between: (i) the inferior colliculus and the dorsal lateral geniculate nucleus, (ii) V1 and the superior colliculus, (iii) the lateral posterior nucleus and V1 and between (iv) the inferior colliculus and the medial geniculate nucleus. We also show unambiguously that the auditory subcortical structures do not connect the Primary Visual Cortex in the anophthalmic mouse. In particular, we find no evidence of a direct projection from the auditory mesencephalon to the Cortex in this animal model of blindness.