The Experts below are selected from a list of 32523 Experts worldwide ranked by ideXlab platform
Charles D Gilbert - One of the best experts on this subject based on the ideXlab platform.
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topography of contextual modulations mediated by short range interactions in primary visual cortex
Nature, 1999Co-Authors: Aniruddha Das, Charles D GilbertAbstract:Neurons in primary visual cortex (V1) respond differently to a simple visual element presented in isolation from when it is embedded withina complex image. This difference, a specific modulation by surrounding elements in the image, is mediated by short- and long-range connections within V1 and by feedback from other areas. Here we study the role of short-range connections in this process, and relate it to the layout of local inhomogeneities in the cortical Maps of Orientation and space. By measuring correlation between neuron pairs located in optically imaged Maps of V1 Orientation columns we show that the strength of local connections between cells is a graded function of lateral separation across cortex, largely radially symmetrical and relatively independent of Orientation preferences. We then show the contextual influence of flanking visual elements on neuronal responses varies systematically with a neuron's position within the cortical Orientation Map. The strength of this contextual influence on a neuron can be predicted from a model of local connections based on simple overlap with particular features of the Orientation Map. This indicates that local intracortical circuitry could endow neurons with a graded specialization for processing angular visual features such as corners and T junctions, and this specialization could have its own functional cortical Map, linked with the Orientation Map.
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distortions of visuotopic Map match Orientation singularities in primary visual cortex
Nature, 1997Co-Authors: Aniruddha Das, Charles D GilbertAbstract:The Map of Orientation columns in primary visual cortex (V1) is known to show strong local distortions, with a generally smooth progression of Orientation preference across extended regions of cortex, interrupted by sharp jumps (fractures) and point singularities. The Map of visual space on V1, in contrast, has been assumed to be locally smooth and isotropic. We find, on the contrary, that the Map of visual space on cat V1 shows strong and systematic local distortions in register with inhomogeneities in the Orientation Map, with the rate of receptive field movement across cortex being largely proportional to the local rate of change of Orientation. This suggests possible systematic local variations in the functional connectivity of short-range lateral connections that underlie local cortical processing.
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long range horizontal connections and their role in cortical reorganization revealed by optical recording of cat primary visual cortex
Nature, 1995Co-Authors: Aniruddha Das, Charles D GilbertAbstract:The cortical 'point spread' (PS) is the area of cortex activated by a minimal visual stimulus. Here we use the PS to explore the functional role of lateral connectivity in normal cat primary visual cortex (V1) and its involvement in topographic reorganization of cortex following retinal lesions. We compared the distributions of PSs measured with optical recording, which reflects both spiking and subthreshold activity, with those measured with extracellular electrodes, which reveal spiking activity alone. The spiking PS represented only 5% of the area of activation shown in the optical PS, indicating that the remaining 95% was probably generated by subthreshold activation. The Orientation dependence of the pattern of the subthreshold activation and its close match with Orientation columns suggests that long-range horizontal connections radiating from the locus of spiking activity were responsible for the observed activation. The spike PS showed anisotropies and inhomogeneities that were related to the pattern of Orientation columns and indicated distortions in the representation of visual space on the cortical surface. In the reorganized cortex the spike PS expanded, approximating the extent of the optical PS seen in normal cortex, and suggesting that reorganization was mediated by an unmasking of normally subthreshold activation to suprathreshold levels. The Orientation Map of the reorganized cortex showed a close match to that obtained before placing the lesion, despite the large shift in topography, supporting the idea that intrinsic horizontal connections were responsible for the reMapping.
Zoltan F Kisvarday - One of the best experts on this subject based on the ideXlab platform.
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axon topography of layer 6 spiny cells to Orientation Map in the primary visual cortex of the cat area 18
Brain Structure & Function, 2017Co-Authors: Katalin Sari, Fuyuki Karube, Zoltan F KisvardayAbstract:To uncover the functional topography of layer 6 neurons, optical imaging was combined with three-dimensional neuronal reconstruction. Apical dendrite morphology of 23 neurons revealed three distinct types. Type Aa possessed a short apical dendrite with many oblique branches, Type Ab was characterized by a short and less branched apical dendrite, whereas Type B had a long apical dendrite with tufts in layer 2. Each type had a similar number of boutons, yet their spatial distribution differed from each other in both radial and horizontal extent. Boutons of Type Aa and Ab were almost restricted to the column of the parent soma with a laminar preference to layer 4 and 5/6, respectively. Only Type B contributed to long horizontal connections (up to 1.5 mm) mostly in deep layers. For all types, bouton distribution on Orientation Map showed an almost equal occurrence at iso- (52.6 ± 18.8 %) and non-iso-Orientation (oblique, 27.7 ± 14.9 % and cross-Orientation 19.7 ± 10.9 %) sites. Spatial convergence of axons of nearby layer 6 spiny neurons depended on soma separation of the parent cells, but only weakly on Orientation preference, contrary to Orientation dependence of converging axons of layer 4 spiny cells. The results show that layer 6 connections have only a weak dependence on Orientation preference compared with those of layers 2/3 (Buzas et al., J Comp Neurol 499:861–881, 2006) and 4 (Karube and Kisvarday, Cereb Cortex 21:1443–1458, 2011).
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axon topography of layer iv spiny cells to Orientation Map in the cat primary visual cortex area 18
Cerebral Cortex, 2011Co-Authors: Fuyuki Karube, Zoltan F KisvardayAbstract:Our aim was to reveal the relationship between layer IV horizontal connections and the functional architecture of the cat primary visual cortex because these connections play important roles in the first cortical stage of visual signals integration. We investigated bouton distribution of spiny neurons over an Orientation preference Map using in vivo optical imaging, unit recordings, and single neuron reconstructions. The radial extent of reconstructed axons (14 star pyramidal and 9 spiny stellate cells) was ~1.5 mm. In the vicinity of the parent somata (<400 mm), boutons occupied chiefly iso-Orientations, however, more distally, 7 cells projected preferentially to non--iso-Orientations. Boutons of each cell were partitioned into 1--15 distinct clusters based on the mean-shift algorithm, of which 57 clusters preferred iso-Orientations and 43 clusters preferred cross-Orientations, each showing sharp Orientation preference ‘‘tuning.’’ However, unlike layer III/V pyramidal cells preferring chiefly iso-Orientations, layer IV cells were engaged with broad Orientations because each bouton cluster from the same cell could show different Orientation preference. These results indicate that the circuitry of layer IV spiny cells is organized differently from that of iso-Orientation dominant layer III/V cells and probably processes visual signals in a different manner from that of the superficial and deeper layers.
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independence of visuotopic representation and Orientation Map in the visual cortex of the cat
European Journal of Neuroscience, 2003Co-Authors: Peter Buzas, Maxim Volgushev, Ulf T Eysel, Zoltan F KisvardayAbstract:The representations of visual space and stimulus Orientation were Mapped in the cat primary visual cortex using electrophysiological recordings supplemented with intrinsic signal optical imaging. The majority of units displaced up to 600 micro m laterally had overlapping RFs both in Orientation domains and around singularities of the Orientation Map. Quantitative comparison of these units revealed only a weak, positive correlation between the difference in their preferred Orientations and RF separations (area 17: r = 0.09; area 18: r = 0.15). The occurrence of nonoverlapping RFs could be accounted for by random RF position scatter rather than by Orientation difference between the units. Monte Carlo analysis showed that our findings are compatible with a locally smooth and linear representation of visual space that is not coupled to the representation of stimulus Orientation. An important functional implication of the above Map relationships is that positional information captured by the retina is faithfully transmitted into the cortex.
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relationship between lateral inhibitory connections and the topography of the Orientation Map in cat visual cortex
European Journal of Neuroscience, 1994Co-Authors: Zoltan F Kisvarday, Ulf T Eysel, Daeshik Kim, Tobias BonhoefferAbstract:The functional and structural topography of lateral inhibitory connections was investigated in visual cortical area 18 using a combination of optical imaging and anatomical tracing techniques in the same tissue. Orientation Maps were obtained by recording intrinsic signals in regions of 8.4-19 mm2. To reveal the inhibitory connections provided by large basket cells, biocytin was iontophoretically injected at identified Orientation sites guided by the pattern of surface blood vessels. The axonal and dendritic fields of two retrogradely labelled large basket cells were reconstructed in layer III. Their axonal fields extended up to 1360 microns from the parent somata. In addition to single basket cells, the population of labelled basket cell axons was also studied. For this analysis anterogradely labelled basket axons running horizontally over 460-1280 microns from the core of an injection site in layer III were taken into account. The distribution of large basket cell terminals according to Orientation preferences of their target regions was quantitatively assessed. Using the same spatial resolution as the Orientation Map, a frequency distribution of basket cell terminals dependent on Orientation specificity could be derived. For individual basket cells, the results showed that, on average, 43% of the terminals provided input to sites showing similar Orientation preferences (+/- 30 degrees) to those of the parent somata. About 35% of the terminals were directed to sites representing oblique-Orientation [+/- (30-60) degrees], and 22% of them terminated at cross-Orientation sites [+/- (60-90) degrees]. Furthermore, the possible impact of large basket cells on target cells at different distances and Orientation preferences was estimated by comparing the occurrence of Orientation preferences with the occurrence of basket terminals on the distance scale. It was found that a basket cell could elicit iso-Orientation inhibition with a high impact between 100-400 and 800-1200 microns, strong cross-Orientation inhibition at approximately 400-800 microns, and oblique-Orientation inhibition between 300-500 and 700-900 microns from the parent soma. The non-isotropic topography of large basket axons suggests a complex function for this cell class, possibly including inhibition related to Orientation and direction selectivity depending on the location of the target cells and possible target selectivity.
Aniruddha Das - One of the best experts on this subject based on the ideXlab platform.
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topography of contextual modulations mediated by short range interactions in primary visual cortex
Nature, 1999Co-Authors: Aniruddha Das, Charles D GilbertAbstract:Neurons in primary visual cortex (V1) respond differently to a simple visual element presented in isolation from when it is embedded withina complex image. This difference, a specific modulation by surrounding elements in the image, is mediated by short- and long-range connections within V1 and by feedback from other areas. Here we study the role of short-range connections in this process, and relate it to the layout of local inhomogeneities in the cortical Maps of Orientation and space. By measuring correlation between neuron pairs located in optically imaged Maps of V1 Orientation columns we show that the strength of local connections between cells is a graded function of lateral separation across cortex, largely radially symmetrical and relatively independent of Orientation preferences. We then show the contextual influence of flanking visual elements on neuronal responses varies systematically with a neuron's position within the cortical Orientation Map. The strength of this contextual influence on a neuron can be predicted from a model of local connections based on simple overlap with particular features of the Orientation Map. This indicates that local intracortical circuitry could endow neurons with a graded specialization for processing angular visual features such as corners and T junctions, and this specialization could have its own functional cortical Map, linked with the Orientation Map.
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distortions of visuotopic Map match Orientation singularities in primary visual cortex
Nature, 1997Co-Authors: Aniruddha Das, Charles D GilbertAbstract:The Map of Orientation columns in primary visual cortex (V1) is known to show strong local distortions, with a generally smooth progression of Orientation preference across extended regions of cortex, interrupted by sharp jumps (fractures) and point singularities. The Map of visual space on V1, in contrast, has been assumed to be locally smooth and isotropic. We find, on the contrary, that the Map of visual space on cat V1 shows strong and systematic local distortions in register with inhomogeneities in the Orientation Map, with the rate of receptive field movement across cortex being largely proportional to the local rate of change of Orientation. This suggests possible systematic local variations in the functional connectivity of short-range lateral connections that underlie local cortical processing.
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long range horizontal connections and their role in cortical reorganization revealed by optical recording of cat primary visual cortex
Nature, 1995Co-Authors: Aniruddha Das, Charles D GilbertAbstract:The cortical 'point spread' (PS) is the area of cortex activated by a minimal visual stimulus. Here we use the PS to explore the functional role of lateral connectivity in normal cat primary visual cortex (V1) and its involvement in topographic reorganization of cortex following retinal lesions. We compared the distributions of PSs measured with optical recording, which reflects both spiking and subthreshold activity, with those measured with extracellular electrodes, which reveal spiking activity alone. The spiking PS represented only 5% of the area of activation shown in the optical PS, indicating that the remaining 95% was probably generated by subthreshold activation. The Orientation dependence of the pattern of the subthreshold activation and its close match with Orientation columns suggests that long-range horizontal connections radiating from the locus of spiking activity were responsible for the observed activation. The spike PS showed anisotropies and inhomogeneities that were related to the pattern of Orientation columns and indicated distortions in the representation of visual space on the cortical surface. In the reorganized cortex the spike PS expanded, approximating the extent of the optical PS seen in normal cortex, and suggesting that reorganization was mediated by an unmasking of normally subthreshold activation to suprathreshold levels. The Orientation Map of the reorganized cortex showed a close match to that obtained before placing the lesion, despite the large shift in topography, supporting the idea that intrinsic horizontal connections were responsible for the reMapping.
Tadashi Furuhara - One of the best experts on this subject based on the ideXlab platform.
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analysis of recrystallization behavior of hot deformed austenite reconstructed from ebsd Orientation Maps of lath martensite
Materials Science Forum, 2016Co-Authors: Manabu Kubota, Goro Miyamoto, Kohsaku Ushioda, Tadashi FuruharaAbstract:The recrystallization behavior of hot-deformed austenite of 0.55% C low alloy steels at 900, 850 and 800°C was investigated by a conventional double-hit compression test and a new method which reconstructs the parent austenite Orientation Map from an EBSD (electron backscattering diffraction) Orientation Map of daughter lath martensite. The new method can clearly reconstruct the parent austenite structure at high temperature from the daughter lath martensite structure and we can obtain the information on crystal Orientation of the work-hardened austenite. It was revealed that recrystallization of austenite at 800 °C is significantly retarded by the addition of 0.1% V. The strong texture of parallel to the compression direction develops just after the hot-deformation, but this texture becomes weaker as the recrystallization progresses. By applying the reconstruction method, it becomes possible to evaluate various phenomena related to the hot-deformation of austenite
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analysis of recrystallization behavior of hot deformed austenite reconstructed from electron backscattering diffraction Orientation Maps of lath martensite
Scripta Materialia, 2016Co-Authors: Manabu Kubota, Goro Miyamoto, Kohsaku Ushioda, Tadashi FuruharaAbstract:Abstract The recrystallization behavior of hot-deformed austenite of a 0.55% C steel at 800 °C was investigated by a method of reconstructing the parent austenite Orientation Map from an electron backscattering diffraction Orientation Map of lath martensite. Recrystallized austenite grains were clearly distinguished from un-recrystallized austenite grains. Very good correlation was confirmed between the static recrystallization behavior investigated mechanically by double-hit compression tests and the change in austenite microstructure evaluated by the reconstruction method. The recrystallization behavior of hot-deformed 0.55% C steel at 800 °C is directly revealed and it was observed that by addition of 0.1% V the recrystallization was significantly retarded.
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reconstruction of parent austenite grain structure based on crystal Orientation Map of bainite with and without ausforming
Isij International, 2011Co-Authors: Goro Miyamoto, Naomichi Iwata, Naoki Takayama, Tadashi FuruharaAbstract:By using a reconstruction program recently developed by the present authors, the parent austenite grain structure is reconstructed from the crystal Orientation Map of bainite structure. Local austenite Orientation can be reconstructed from non-ausformed bainite structure with errors of 1.7° and 1.0° at spatial resolutions of 5 and 20 μ m respectively. The angle of errors is further reduced to be less than 0.5° when an analysis area is extended to a whole austenite grain. Application of the reconstruction program to the bainite structure transformed from deformed austenite has clarified that the variation in grain shape and deformation texture of parent austenite can be well reconstructed.
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Mapping the parent austenite Orientation reconstructed from the Orientation of martensite by ebsd and its application to ausformed martensite
Acta Materialia, 2010Co-Authors: Goro Miyamoto, Naomichi Iwata, Naoki Takayama, Tadashi FuruharaAbstract:Abstract A new method is developed for reconstruction of the local Orientation of the parent austenite based on the Orientation of lath martensite measured by electron backscattered diffraction. The local Orientation of austenite was obtained by least squares fitting as the difference between the experimental data and the predicted martensite Orientation was minimal, assuming the specific Orientation relationship (OR) between martensite and the parent austenite. First, the average OR between austenite and lath martensite was precisely determined and it was shown that both close packed planes and directions between martensite and the parent austenite deviated by more than 1° in low carbon martensite. The quality of the reconstructed austenite Orientation Map depended strongly on the OR used for the calculation. When Kurdjumov–Sachs (K–S) or Nishiyama–Wasserman (N–W) ORs were used the austenite Orientation was frequently mis-indexed as a twin Orientation with respect to the true Orientation because of the mirror symmetry of (0 1 1)α stacking in the K–S or N–W ORs. In contrast, the frequency of mis-indexing was significantly reduced by using the measured OR, where the close packed planes and directions were not parallel. The deformation structure in austenite was successfully reconstructed by applying the proposed method to ausformed martensite in low carbon steel.
Gang Wang - One of the best experts on this subject based on the ideXlab platform.
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surround modulation in cortical Orientation Map revealed by optical imaging and its dependency on receptive field eccentricity
European Journal of Neuroscience, 2012Co-Authors: Kanami Uchimura, Junya Okamura, Gang WangAbstract:Optical imaging was used to investigate the difference in surround modulation on Orientation Map related to receptive field eccentricity in cat visual cortex. Presentation of center-surround stimuli at the center of gaze resulted in no clear surround modulation; however, significant modulation was observed in its corresponding cortical area when the center-surround stimuli were presented at 10° eccentricity in more peripheral parts of the visual field. Modulation was observed both in the response magnitude and in the spatial pattern of the response. Surround Orientation perpendicular to the Orientation of a center patch grating showed the largest modulation in the response magnitude. The modulation became weaker as the Orientation difference between the center and surround gratings became smaller. Regardless of the Orientations for the central patch gratings, a similar response spatial pattern was observed in the cortical region where the underlying cells had their receptive fields covering the central patch, if the stimuli were with the same surround gratings. These properties support the notion of a relative specialization for visual information processing in peripheral representations of cortical areas.