The Experts below are selected from a list of 60240 Experts worldwide ranked by ideXlab platform
David J. Freedman - One of the best experts on this subject based on the ideXlab platform.
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Independent Category and Spatial Encoding in Parietal Cortex
Neuron, 2013Co-Authors: Chris A. Rishel, Gang Huang, David J. FreedmanAbstract:Summary The posterior Parietal Cortex plays a central role in spatial functions, such as spatial attention and saccadic eye movements. However, recent work has increasingly focused on the role of Parietal Cortex in encoding nonspatial cognitive factors such as visual categories, learned stimulus associations, and task rules. The relationship between spatial encoding and nonspatial cognitive signals in Parietal Cortex, and whether cognitive signals are robustly encoded in the presence of strong spatial neuronal responses, is unknown. We directly compared nonspatial cognitive and spatial encoding in the lateral intraParietal (LIP) area by training monkeys to perform a visual categorization task during which they made saccades toward or away from LIP response fields (RFs). Here we show that strong saccade-related responses minimally influence robustly encoded category signals in LIP. This suggests that cognitive and spatial signals are encoded independently in LIP and underscores the role of Parietal Cortex in nonspatial cognitive functions. Video Abstract
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Visual categorization and the Parietal Cortex
Frontiers in integrative neuroscience, 2012Co-Authors: Jamie K. Fitzgerald, Sruthi K. Swaminathan, David J. FreedmanAbstract:The primate brain is adept at rapidly grouping items and events into functional classes, or categories, in order to recognize the significance of stimuli and guide behavior. Higher cognitive functions have traditionally been considered the domain of frontal areas. However, increasing evidence suggests that Parietal Cortex is also involved in categorical and associative processes. Previous work showed that the Parietal Cortex is highly involved in spatial processing, attention, and saccadic eye movement planning, and more recent studies have found decision-making signals in lateral intraParietal area (LIP). We recently found that a subdivision of Parietal Cortex, LIP, reflects learned categories for multiple types of visual stimuli. Additionally, a comparison of categorization signals in Parietal and frontal areas found stronger and earlier categorization signals in Parietal Cortex arguing that, in trained animals, Parietal abstract association or category signals are unlikely to arise via feedback from prefrontal Cortex (PFC).
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Posterior Parietal Cortex: Space…and Beyond
Neuron, 2004Co-Authors: David J. FreedmanAbstract:How do we decide how to react to a stimulus or event? To do so requires recognition of the stimulus itself as well as an appreciation of the context within which that stimulus is encountered. In this issue of Neuron, Stoet and Snyder report that neurons in the Parietal Cortex of monkeys can carry contextual information related to the rules that are relevant for solving a visual discrimination task.
David J Heeger - One of the best experts on this subject based on the ideXlab platform.
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topographic maps of visual spatial attention in human Parietal Cortex
Journal of Neurophysiology, 2005Co-Authors: Michael A Silver, David Ress, David J HeegerAbstract:Functional magnetic resonance imaging (fMRI) was used to measure activity in human Parietal Cortex during performance of a visual detection task in which the focus of attention systematically traversed the visual field. Critically, the stimuli were identical on all trials (except for slight contrast changes in a fully randomized selection of the target locations) whereas only the cued location varied. Traveling waves of activity were observed in posterior Parietal Cortex consistent with shifts in covert attention in the absence of eye movements. The temporal phase of the fMRI signal in each voxel indicated the corresponding visual field location. Visualization of the distribution of temporal phases on a flattened representation of Parietal Cortex revealed at least two distinct topographically organized cortical areas within the intraParietal sulcus (IPS), each representing the contralateral visual field. Two cortical areas were proposed based on this topographic organization, which we refer to as IPS1 and IPS2 to indicate their locations within the IPS. This nomenclature is neutral with respect to possible homologies with well-established cortical areas in the monkey brain. The two proposed cortical areas exhibited relatively little response to passive visual stimulation in comparison with early visual areas. These results provide evidence for multiple topographic maps in human Parietal Cortex.
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topographic organization for delayed saccades in human posterior Parietal Cortex
Journal of Neurophysiology, 2005Co-Authors: Denis Schluppeck, Paul W Glimcher, David J HeegerAbstract:Posterior Parietal Cortex (PPC) is thought to play a critical role in decision making, sensory attention, motor intention, and/or working memory. Research on the PPC in non-human primates has focus...
Christopher Kennard - One of the best experts on this subject based on the ideXlab platform.
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Temporal dynamics of Parietal Cortex involvement in visual search
NEUROPSYCHOLOGIA, 2006Co-Authors: Christopher KennardAbstract:The functional-neuroanatomic relationship that describes the involvement of the Parietal Cortex in visual search was investigated using repetitive transcranial magnetic stimulation (rTMS; 10 Hz, 500 ms in duration). Twelve adult participants performed feature-based visual search for a unique letter-without eye movements-under conditions that involved manipulations of search efficiency (efficient versus inefficient) and target-selection demands (set-size: 4 versus 10). rTMS was applied over the right posterior Parietal Cortex at the onset of the search array for all factorial conditions (0-500ms); Stimulation was additionally administered at 500 ms post-array onset (500-1000ms) during inefficient search (set-size 10). Stimulation over the primary sensorimotor Cortex served as a within-subjects control condition, and eye movements were monitored continuously. Significant increases in reaction time were restricted to Parietal Stimulation during inefficient search (set-size 10), with interference observed when rTMS was administered at the onset of the search array and at 500 ms post-array onset. The early effect was confined to target-present trials and the late effect was confined to target-absent trials, which may indicate temporally dissociable Parietal involvement in target detection and response-based selection and/or search termination, respectively. Error rates did not vary significantly as a function of any of the independent variables. Taken together, these results are consistent with evidence from functional magnetic resonance studies indicating that inefficient feature-based visual search requires an intact Parietal Cortex, and also indicate that the Parietal Cortex is involved in inefficient search later than has been previously reported. (c) 2005 Elsevier Ltd. All rights reserved.
Leslie G. Ungerleider - One of the best experts on this subject based on the ideXlab platform.
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Posterior Parietal Cortex and the filtering of distractors
Proceedings of the National Academy of Sciences of the United States of America, 2003Co-Authors: Stacia R. Friedman-hill, Robert Desimone, Lynn C. Robertson, Leslie G. UngerleiderAbstract:Neural systems for visual processing can focus attention on behaviorally relevant objects, filtering out competing distractors. Neurophysiological studies in animals and brain imaging studies in humans suggest that such filtering depends on top-down inputs to extrastriate visual areas, originating in structures important for attentional control. To test whether the posterior Parietal Cortex may be a necessary source of signals that filter distractors, we measured the ability of a patient with bilateral Parietal lesions to discriminate the features of a target surrounded by distractors of variable contrast. In the presence of distractors, the patient was impaired at discriminating both grating orientation and faces, and the magnitude of the impairment increased with distractor salience. These attentional deficits are remarkably similar to those caused by damage to monkey extrastriate regions V4 and/or TEO, which are thought to be recipients of top-down attentional feedback. In contrast to the effects of V4 and TEO lesions, however, the Parietal lesions impaired performance even with widely spaced targets and distractors, a finding consistent with the projections of Parietal Cortex to visual processing areas covering a wide range of receptive field sizes and eccentricities.
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Comparison of subcortical connections of inferior temporal and posterior Parietal Cortex in monkeys
Visual neuroscience, 1993Co-Authors: Joan S. Baizer, Robert Desimone, Leslie G. UngerleiderAbstract:To investigate the subcortical connections of the object vision and spatial vision cortical processing pathways, we injected the inferior temporal and posterior Parietal Cortex of six Rhesus monkeys with retrograde or anterograde tracers. The temporal injections included area TE on the lateral surface of the hemisphere and adjacent portions of area TEO. The Parietal injections covered the posterior bank of the intraParietal sulcus, including areas VIP and LIP. Our results indicate that several structures project to both the temporal and Parietal Cortex, including the medial and lateral pulvinar, claustrum, and nucleus basalis. However, the cells in both the pulvinar and claustrum that project to the two systems are mainly located in different parts of those structures, as are the terminals which arise from the temporal and Parietal Cortex. Likewise, the projections from the temporal and Parietal Cortex to the caudate nucleus and putamen are largely segregated. Finally, we found projections to the pons and superior colliculus from Parietal but not temporal Cortex, whereas we found the lateral basal and medial basal nuclei of the amygdala to be reciprocally connected with temporal but not Parietal Cortex. Thus, the results show that, like the cortical connections of the two visual processing systems, the subcortical connections are remarkably segregated.
Tirin Moore - One of the best experts on this subject based on the ideXlab platform.
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Parietal Cortex Regulates Visual Salience and Salience-Driven Behavior.
Neuron, 2020Co-Authors: Xiaomo Chen, Marc Zirnsak, Gabriel M. Vega, Eshan Govil, Stephen G. Lomber, Tirin MooreAbstract:Summary Unique stimuli stand out. Despite an abundance of competing sensory stimuli, the detection of the most salient ones occurs without effort, and that detection contributes to the guidance of adaptive behavior. Neurons sensitive to the salience of visual stimuli are widespread throughout the primate visual system and are thought to shape the selection of visual targets. However, a neural source of salience remains elusive. In an attempt to identify a source of visual salience, we reversibly inactivated Parietal Cortex and simultaneously recorded salience signals in prefrontal Cortex. Inactivation of Parietal Cortex not only caused pronounced and selective reductions of salience signals in prefrontal Cortex but also diminished the influence of salience on visually guided behavior. These observations demonstrate a causal role of Parietal Cortex in regulating salience signals within the brain and in controlling salience-driven behavior.
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The Contribution of Parietal Cortex to Visual Salience
2019Co-Authors: Xiaomo Chen, Marc Zirnsak, Gabriel M. Vega, Eshan Govil, Stephen G. Lomber, Tirin MooreAbstract:Abstract Unique stimuli stand out. In spite of an abundance of competing sensory stimuli, the detection of the most salient ones occurs without effort, and that detection contributes to the guidance of adaptive behavior. Neurons sensitive to the salience of visual stimuli are widespread throughout the primate visual system and are thought to shape the selection of visual targets. However, mechanisms underlying the representation of salience remain elusive. Among the possible candidates are areas within posterior Parietal Cortex, which appear to be crucial in the control of visual attention and are thought to play a unique role in representing stimulus salience. Here we show that reversible inactivation of Parietal Cortex not only selectively reduces the representation of visual salience within the brain, but it also diminishes the influence of salience on visually guided behavior. These results demonstrate a distinct contribution of Parietal areas to vision and visual attention.
