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Layer-Dependent Attentional Processing by Top-down Signals in a Visual Cortical Microcircuit Model  [PDF]
Nobuhiko Wagatsuma,Tobias C. Potjans
Frontiers in Computational Neuroscience , 2011, DOI: 10.3389/fncom.2011.00031
Abstract: A vast amount of information about the external world continuously flows into the brain, whereas its capacity to process such information is limited. Attention enables the brain to allocate its resources of information processing to selected sensory inputs for reducing its computational load, and effects of attention have been extensively studied in visual information processing. However, how the microcircuit of the visual cortex processes attentional information from higher areas remains largely unknown. Here, we explore the complex interactions between visual inputs and an attentional signal in a computational model of the visual cortical microcircuit. Our model not only successfully accounts for previous experimental observations of attentional effects on visual neuronal responses, but also predicts contrasting differences in the attentional effects of top-down signals between cortical layers: attention to a preferred stimulus of a column enhances neuronal responses of layers 2/3 and 5, the output stations of cortical microcircuits, whereas attention suppresses neuronal responses of layer 4, the input station of cortical microcircuits. We demonstrate that the specific modulation pattern of layer-4 activity, which emerges from inter-laminar synaptic connections, is crucial for a rapid shift of attention to a currently unattended stimulus. Our results suggest that top-down signals act differently on different layers of the cortical microcircuit.
Lateral interactions in visual perception of temporal signals: cortical and subcortical components
Teixeira, Claudio E. C.;Silveira, Luiz Carlos L.;Kremers, Jan;
Psychology & Neuroscience , 2011, DOI: 10.3922/j.psns.2011.1.007
Abstract: the aim of this work was to isolate and investigate subcortical and cortical lateral interactions involved in flicker perception. we quantified the perceived flicker strength (pfs) in the center of a test stimulus which was simultaneously modulated with a surround stimulus (50% michelson contrast in both stimuli). subjects were requested to adjust the modulation depth of a separate matching stimulus that was physically identical to the center of the test stimulus but without the surround. using lcd goggles, synchronized to the frame rate of a crt screen, the center and surround could be presented monoptically or dichoptically. in the monoptic condition, center-surround interactions can have both subcortical and cortical origins. in the dichoptic condition, center-surround interactions cannot occur in the retina and the lgn, therefore isolating a cortical mechanism. results revealed both a strong monoptic (subcortical plus cortical) lateral interaction and a weaker dichoptic (cortical) lateral interaction. subtraction of the dichoptic from the monoptic data revealed a subcortical mechanism of the lateral interaction. while the modulation of the cortical pfs component showed a low-pass temporal-frequency tuning, the modulation of the subcortical pfs component was maximal at 6 hz. these findings are consistent with two separate temporal channels influencing the monoptic pfs, each with distinct lateral interactions strength and frequency tuning characteristics. we conclude that both subcortical and cortical lateral interactions modulate flicker perception.
Lateral interactions in visual perception of temporal signals: cortical and subcortical components
Claudio E. C. Teixeira,Luiz Carlos L. Silveira,Jan Kremers
Psychology & Neuroscience , 2011,
Abstract: The aim of this work was to isolate and investigate subcortical and cortical lateral interactions involved in ficker perception. We quantifed the perceived ficker strength (PFS) in the center of a test stimulus which was simultaneously modulated with a surround stimulus (50% Michelson contrast in both stimuli). Subjects were requested to adjust the modulation depth of a separate matching stimulus that was physically identical to the center of the test stimulus but without the surround. Using LCD goggles, synchronized to the frame rate of a CRT screen, the center and surround could be presented monoptically or dichoptically. In the monoptic condition, center-surround interactions can have both subcortical and cortical origins. In the dichoptic condition, center-surround interactions cannot occur in the retina and the LGN, therefore isolating a cortical mechanism. Results revealed both a strong monoptic (subcortical plus cortical) lateral interaction and a weaker dichoptic (cortical) lateral interaction. Subtraction of the dichoptic from the monoptic data revealed a subcortical mechanism of the lateral interaction. While the modulation of the cortical PFS component showed a low-pass temporal-frequency tuning, the modulation of the subcortical PFS component was maximal at 6 Hz. These fndings are consistent with two separate temporal channels infuencing the monoptic PFS, each with distinct lateral interactions strength and frequency tuning characteristics. We conclude that both subcortical and cortical lateral interactions modulate ficker perception.
Visual motion integration is mediated by directional ambiguities in local motion signals  [PDF]
Francesca Rocchi,Tim Ledgeway,Ben S. Webb
Frontiers in Computational Neuroscience , 2013, DOI: 10.3389/fncom.2013.00167
Abstract: The output of primary visual cortex (V1) is a piecemeal representation of the visual scene and the response of any one cell cannot unambiguously guide sensorimotor behavior. It remains unsolved how subsequent stages of cortical processing combine (“pool”) these early visual signals into a coherent representation. We (Webb et al., 2007, 2011) have shown that responses of human observers on a pooling task employing broadband, random dot motion can be accurately predicted by decoding the maximum likelihood direction from a population of motion-sensitive neurons. Whereas Amano et al. (2009) found that the vector average velocity of arrays of narrowband, two-dimensional (2-d) plaids predicts perceived global motion. To reconcile these different results, we designed two experiments in which we used 2-d noise textures moving behind spatially distributed apertures and measured the point of subjective equality between pairs of global noise textures. Textures in the standard stimulus moved rigidly in the same direction, whereas their directions in the comparison stimulus were sampled from a set of probability distributions. Human observers judged which noise texture had a more clockwise (CW) global direction. In agreement with Amano and colleagues, observers' perceived global motion coincided with the vector average stimulus direction. To test if directional ambiguities in local motion signals governed perceived global direction, we manipulated the fidelity of the texture motion within each aperture. A proportion of the apertures contained texture that underwent rigid translation and the remainder contained dynamic (temporally uncorrelated) noise to create locally ambiguous motion. Perceived global motion matched the vector average when the majority of apertures contained rigid motion, but with increasing levels of dynamic noise shifted toward the maximum likelihood direction. A class of population decoders utilizing power-law non-linearities can accommodate this flexible pooling.
PROGRESS IN VISUAL CORTICAL RESEARCH USING OPTICAL IMAGING BASED ON INTRINSIC SIGNALS
应用基于内源信号的光学成像技术的视觉脑研究现状

ZHANG Kun,YU Hong-bo,SHOU Tian-de,
张鹍
,俞洪波,寿天德

动物学研究 , 2000,
Abstract: Optical imaging based on intrinsic signals is a newly emerged technique to detect the functional signals in the brain.Since it has no toxic effect and could provide a high spatial resolution it has been widely used in the functional architecture study of the visual,auditory and somatosensory cortex.In this paper,we introduced the recent progress on the vision research using this technique,and compared it with other brain functional imaging technique and single unit recording.We established the first optical imaging system in China.Using this system,the orientation map has been successfully recorded in the primary visual cortex in the cat at different depths,By now,a lot of work has been done with the system recently.
Heterogeneity and dynamics of cortical populations coding visual detection  [PDF]
Jorrit S. Montijn,Pieter M. Goltstein,Cyriel M. A. Pennartz
Quantitative Biology , 2015,
Abstract: Previous studies have demonstrated the importance of the primary sensory cortex for the detection, discrimination and awareness of visual stimuli, but it is unknown how neuronal populations in this area process detected and undetected stimuli differently. Critical differences may reside in the mean strength of responses to visual stimuli, as reflected in bulk signals detectable in fMRI, EEG or MEG studies, or may be more subtly composed of differentiated activity of individual sensory neurons. Quantifying single-cell Ca2+ responses to visual stimuli recorded with in vivo 2-photon imaging, we found that visual detection correlates more strongly with population response heterogeneity rather than overall response strength. Moreover, neuronal populations showed consistencies in activation patterns across temporally spaced trials in association with hit responses, but not during non-detections. Contrary to models relying on temporally stable networks or bulk-signaling, these results suggest that detection depends on transient differentiation in neuronal activity within cortical populations.
Six principles of visual cortical dynamics  [PDF]
Per E. Roland
Frontiers in Systems Neuroscience , 2010, DOI: 10.3389/fnsys.2010.00028
Abstract: A fundamental goal in vision science is to determine how many neurons in how many areas are required to compute a coherent interpretation of the visual scene. Here I propose six principles of cortical dynamics of visual processing in the first 150 ms following the appearance of a visual stimulus. Fast synaptic communication between neurons depends on the driving neurons and the biophysical history and driving forces of the target neurons. Under these constraints, the retina communicates changes in the field of view driving large populations of neurons in visual areas into a dynamic sequence of feed-forward communication and integration of the inward current of the change signal into the dendrites of higher order area neurons (30–70 ms). Simultaneously an even larger number of neurons within each area receiving feed-forward input are pre-excited to sub-threshold levels. The higher order area neurons communicate the results of their computations as feedback adding inward current to the excited and pre-excited neurons in lower areas. This feedback reconciles computational differences between higher and lower areas (75–120 ms). This brings the lower area neurons into a new dynamic regime characterized by reduced driving forces and sparse firing reflecting the visual areas interpretation of the current scene (140 ms). The population membrane potentials and net-inward/outward currents and firing are well behaved at the mesoscopic scale, such that the decoding in retinotopic cortical space shows the visual areas’ interpretation of the current scene. These dynamics have plausible biophysical explanations. The principles are theoretical, predictive, supported by recent experiments and easily lend themselves to experimental tests or computational modeling.
Visual neglect in posterior cortical atrophy
Katia Andrade, Dalila Samri, Marie Sarazin, Leonardo C de Souza, Laurent Cohen, Michel de Schotten, Bruno Dubois, Paolo Bartolomeo
BMC Neurology , 2010, DOI: 10.1186/1471-2377-10-68
Abstract: Twenty-four right-handed PCA patients underwent a standardized battery of neglect tests. Visual fields were examined clinically by the confrontation method.Sixteen of the 24 patients (66%) had signs of visual neglect on at least one test, and fourteen (58%) also had visual extinction or hemianopia. Five patients (21%) had neither neglect nor visual field defects. As expected, left-sided neglect was more severe than right-sided neglect. However, right-sided neglect resulted more frequently in this population (29%) than in previous studies on focal brain lesions.When assessed with specific visuospatial tests, visual neglect is frequent in patients with PCA. Diagnosis of neglect is important because of its negative impact on daily activities. Clinicians should consider the routine use of neglect tests to screen patients with high-level visual deficits. The relatively high frequency of right-sided neglect in neurodegenerative patients supports the hypothesis that bilateral brain damage is necessary for right-sided neglect signs to occur, perhaps because of the presence in the right hemisphere of crucial structures whose damage contributes to neglect.Posterior cortical atrophy (PCA) is a rare, early-onset neurodegenerative disease, characterized by a progressive impairment of higher order visual functions out of proportion to other cognitive disabilities [1] and occipito-parietal damage, which is often more severe in the right hemisphere [2,3]. Asymmetric parietal damage might predict a frequent occurrence of visual neglect and related disorders such as visual extinction in PCA patients. Despite this, neglect and extinction appear to be relatively rare findings in PCA [4,5] mainly observed late in the course of the disease [1]. However, neglect may easily pass undetected if not assessed with specific tests [6]. Thus, a study employing specific neglect tests [7] revealed signs of left-sided neglect in six patients, and of right-sided neglect in one patient out of a group
Coverage, continuity, and visual cortical architecture  [cached]
Keil Wolfgang,Wolf Fred
Neural Systems & Circuits , 2011, DOI: 10.1186/2042-1001-1-17
Abstract: Background The primary visual cortex of many mammals contains a continuous representation of visual space, with a roughly repetitive aperiodic map of orientation preferences superimposed. It was recently found that orientation preference maps (OPMs) obey statistical laws which are apparently invariant among species widely separated in eutherian evolution. Here, we examine whether one of the most prominent models for the optimization of cortical maps, the elastic net (EN) model, can reproduce this common design. The EN model generates representations which optimally trade of stimulus space coverage and map continuity. While this model has been used in numerous studies, no analytical results about the precise layout of the predicted OPMs have been obtained so far. Results We present a mathematical approach to analytically calculate the cortical representations predicted by the EN model for the joint mapping of stimulus position and orientation. We find that in all the previously studied regimes, predicted OPM layouts are perfectly periodic. An unbiased search through the EN parameter space identifies a novel regime of aperiodic OPMs with pinwheel densities lower than found in experiments. In an extreme limit, aperiodic OPMs quantitatively resembling experimental observations emerge. Stabilization of these layouts results from strong nonlocal interactions rather than from a coverage-continuity-compromise. Conclusions Our results demonstrate that optimization models for stimulus representations dominated by nonlocal suppressive interactions are in principle capable of correctly predicting the common OPM design. They question that visual cortical feature representations can be explained by a coverage-continuity-compromise.
Coverage, Continuity and Visual Cortical Architecture  [PDF]
Wolfgang Keil,Fred Wolf
Quantitative Biology , 2011,
Abstract: The primary visual cortex of many mammals contains a continuous representation of visual space, with a roughly repetitive aperiodic map of orientation preferences superimposed. It was recently found that orientation preference maps (OPMs) obey statistical laws which are apparently invariant among species widely separated in eutherian evolution. Here, we examine whether one of the most prominent models for the optimization of cortical maps, the elastic net (EN) model, can reproduce this common design. The EN model generates representations which optimally trade of stimulus space coverage and map continuity. While this model has been used in numerous studies, no analytical results about the precise layout of the predicted OPMs have been obtained so far. We present a mathematical approach to analytically calculate the cortical representations predicted by the EN model for the joint mapping of stimulus position and orientation. We find that in all previously studied regimes, predicted OPM layouts are perfectly periodic. An unbiased search through the EN parameter space identifies a novel regime of aperiodic OPMs with pinwheel densities lower than found in experiments. In an extreme limit, aperiodic OPMs quantitatively resembling experimental observations emerge. Stabilization of these layouts results from strong nonlocal interactions rather than from a coverage-continuity-compromise. Our results demonstrate that optimization models for stimulus representations dominated by nonlocal suppressive interactions are in principle capable of correctly predicting the common OPM design. They question that visual cortical feature representations can be explained by a coverage-continuity-compromise.
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