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David C Van Essen

Publications and source records attributed to David C Van Essen.

At least 19 recordsLinked to original sources
PubMed2006

A comparative study of shape representation in macaque visual areas v2 and v4.

We compared aspects of shape representation in extrastriate visual areas V2 and V4, which are both implicated in shape processing and belong to different hierarchical levels. We recorded responses of cells in awake, fixating monkeys to matched sets of contour and grating stimuli of low or intermediate complexity. These included simple stimuli (bars and sinusoids) and more complex stimuli (angles, intersections, arcs, and non-Cartesian gratings), all scaled to receptive field size. The responses of cells within each area were substantially modulated by each shape characteristic tested, with substantial overlap between areas by many response measures. Our analyses revealed many clear and reliable differences between areas in terms of the effectiveness of, and response modulation by, various shape characteristics. Grating stimuli were on average more effective than contour stimuli in V2 and V4, but the difference was more pronounced in V4. As a population, V4 showed greater response modulation by some shape characteristics (including simple shape characteristics) and V2 showed greater response modulation by many others (including complex shape characteristics). Recordings from area V1 demonstrated complex shape selectivity in some cells and relatively modest population differences in comparison with V2. Altogether, the representation of 2-dimensional shape characteristics revealed by this analysis varies substantially among the 3 areas. But surprisingly, the differences revealed by our analyses, individually or collectively, do not parallel the stepwise organization of the anatomical hierarchy. Commonalities of visual shape representation across hierarchical levels may reflect the replication of neural circuits used in generating complex shape representations at multiple spatial scales.

Animals↗
PubMed2006

Symmetry of cortical folding abnormalities in Williams syndrome revealed by surface-based analyses.

We analyzed folding abnormalities in the cerebral cortex of subjects with Williams syndrome (WS), a genetically based developmental disorder, using surface-based analyses applied to structural magnetic resonance imaging data. Surfaces generated from each individual hemisphere were registered to a common atlas target (the PALS-B12 atlas). Maps of sulcal depth (distance from the cerebral hull) were combined across individuals to generate maps of average sulcal depth for WS and control subjects, along with depth-difference maps and t-statistic maps that accounted for within-group variability. Significant structural abnormalities were identified in 33 locations, arranged as 16 bilaterally symmetric pairs plus a lateral temporal region in the right hemisphere. Discrete WS folding abnormalities extended across a broad swath from dorsoposterior to ventroanterior regions of each hemisphere, in cortical areas associated with multiple sensory modalities as well as regions implicated in cognitive and emotional behavior. Hemispheric asymmetry in the temporal cortex is reduced in WS compared with control subjects. These findings provide insights regarding possible developmental mechanisms that give rise to folding abnormalities and to the spectrum of behavioral characteristics associated with WS.

Adolescent↗
PubMed2005

A Population-Average, Landmark- and Surface-based (PALS) atlas of human cerebral cortex.

This report describes a new electronic atlas of human cerebral cortex that provides a substrate for a wide variety of brain-mapping analyses. The Population-Average, Landmark- and Surface-based (PALS) atlas approach involves surface-based and volume-based representations of cortical shape, each available as population averages and as individual subject data. The specific PALS-B12 atlas introduced here is derived from structural MRI volumes of 12 normal young adults. Accurate cortical surface reconstructions were generated for each hemisphere, and the surfaces were inflated, flattened, and mapped to standard spherical configurations using SureFit and Caret software. A target atlas sphere was generated by averaging selected landmark contours from each of the 24 contributing hemispheres. Each individual hemisphere was deformed to this target using landmark-constrained surface registration. The utility of the resultant PALS-B12 atlas was demonstrated using a variety of analyses. (i) Probabilistic maps of sulcal identity were generated using both surface-based registration (SBR) and conventional volume-based registration (VBR). The SBR approach achieved markedly better consistency of sulcal alignment than did VBR. (ii) A method is introduced for 'multi-fiducial mapping' of volume-averaged group data (e.g., fMRI data, probabilistic architectonic maps) onto each individual hemisphere in the atlas, followed by spatial averaging across the individual maps. This yielded a population-average surface representation that circumvents the biases inherent in choosing any single hemisphere as a target. (iii) Surface-based and volume-based morphometry applied to maps of sulcal depth and sulcal identity demonstrated prominent left-right asymmetries in and near the superior temporal sulcus and Sylvian fissure. Moreover, shape variability in the temporal lobe is significantly greater in the left than the right hemisphere. The PALS-B12 atlas has been registered to other surface-based atlases to facilitate interchange of data and comparison across atlases. All data sets in the PALS-B12 atlas are accessible via the SumsDB database for online and offline visualization and analysis.

Adolescent↗
PubMed2005

Role of primate visual area V4 in the processing of 3-D shape characteristics defined by disparity.

We studied the responses of V4 neurons in awake, fixating monkeys to a diverse set of stereoscopic stimuli, including zero-order disparity (frontoparallel) stimuli, surfaces oriented in depth, and convex and concave shapes presented at various mean disparities. The responses of many V4 cells were significantly modulated across each of these stimulus subsets. In general, V4 cells were broadly tuned for zero-order disparity, and at any given disparity value, about four-fifths of the cells responded significantly above background. The response modulation by flat surfaces oriented in depth was significant for about one-quarter of cells, and the responses of about one-third of the cells were significantly modulated by convex or concave surfaces at various mean disparities. However, we encountered no cells that unambiguously distinguished a given three-dimensional (3-D) shape independent of mean disparity. Thus 3-D shapes defined by disparity are unlikely to be represented explicitly at the level of individual V4 cells. Nonetheless, V4 cells likely play an important role in the processing of 3-D shape characteristics defined by disparity as a part of a distributed network.

Analysis of Variance↗
PubMed2005

The human brain is intrinsically organized into dynamic, anticorrelated functional networks.

During performance of attention-demanding cognitive tasks, certain regions of the brain routinely increase activity, whereas others routinely decrease activity. In this study, we investigate the extent to which this task-related dichotomy is represented intrinsically in the resting human brain through examination of spontaneous fluctuations in the functional MRI blood oxygen level-dependent signal. We identify two diametrically opposed, widely distributed brain networks on the basis of both spontaneous correlations within each network and anticorrelations between networks. One network consists of regions routinely exhibiting task-related activations and the other of regions routinely exhibiting task-related deactivations. This intrinsic organization, featuring the presence of anticorrelated networks in the absence of overt task performance, provides a critical context in which to understand brain function. We suggest that both task-driven neuronal responses and behavior are reflections of this dynamic, ongoing, functional organization of the brain.

Attention↗
PubMed2005

Corticocortical and thalamocortical information flow in the primate visual system.

Visual cortex in primates contains a mosaic of several dozen visual areas that collectively occupy a large fraction of cerebral cortex (approximately 50% in the macaque; approximately 25% in humans). These areas are richly interconnected by hundreds of reciprocal corticocortical pathways that underlie an anatomically based hierarchy containing multiple processing streams. In addition, there is a complex pattern of reciprocal connections with the pulvinar, which itself contains about 10 architectonically distinct subdivisions. Information flow through these corticocortical and corticothalamic circuits is regulated very dynamically by top-down as well as bottom-up processes, including directed visual attention. This chapter evaluates current hypotheses and evidence relating to the interaction between thalamocortical and corticocortical circuitry in the dynamic regulation of information flow.

Animals↗
PubMed2004

Peaked encoding of relative luminance in macaque areas V1 and V2.

It is widely presumed that throughout the primate visual pathway neurons encode the relative luminance of objects (at a given light adaptation level) using two classes of monotonic function, one positively and the other negatively sloped. Based on computational considerations, we hypothesized that early visual cortex also contains neurons preferring intermediate relative luminance values. We tested this hypothesis by recording from single neurons in areas V1 and V2 of alert, fixating macaque monkeys during presentation of a large, spatially uniform patch oscillating slowly in luminance and surrounded by a static texture background. A substantial subset of neurons responsive to such low spatial frequency luminance stimuli in both areas exhibited prominent and statistically reliable response peaks to intermediate rather than minimal or maximal luminance values. When presented with static patches of different luminance but of the same spatial configuration, most neurons tested retained a preference for intermediate relative luminance. Control experiments using luminance modulation at multiple low temporal frequencies or reduced amplitude indicate that in the slow luminance-oscillating paradigm, responses were more strongly modulated by the luminance level than the rate of luminance change. These results strongly support our hypothesis and reveal a striking cortical transformation of luminance-related information that may contribute to the perception of surface brightness and lightness. In addition, we tested many luminance-sensitive neurons with large chromatic patches oscillating slowly in luminance. Many cells, including the gray-preferring neurons, exhibited strong color preferences, suggesting a role of luminance-sensitive cells in encoding information in three-dimensional color space.

Action Potentials↗
PubMed2004

Stimulus dependence of disparity coding in primate visual area V4.

Disparity tuning in visual cortex has been shown using a variety of stimulus types that contain stereoscopic depth cues. It is not known whether different stimuli yield similar disparity tuning curves. We studied whether cells in visual area V4 of the macaque show similar disparity tuning profiles when the same set of disparity values were tested using bars or dynamic random dot stereograms, which are among the most commonly used stimuli for this purpose. In a majority of V4 cells (61%), the shape of the disparity tuning profile differed significantly for the two stimulus types. The two sets of stimuli yielded statistically indistinguishable disparity tuning profiles for only a small minority (6%) of V4 cells. These results indicate that disparity tuning in V4 is stimulus-dependent. Given the fact that bar stimuli contain two-dimensional (2-D) shape cues, and the random dot stereograms do not, our results also indicate that V4 cells represent 2-D shape and binocular disparity in an interdependent fashion, revealing an unexpected complexity in the analysis of depth and three-dimensional shape.

Analysis of Variance↗
PubMed2004

Temporal dynamics of shape analysis in macaque visual area V2.

The firing rate of visual cortical neurons typically changes substantially during a sustained visual stimulus. To assess whether, and to what extent, the information about shape conveyed by neurons in visual area V2 changes over the course of the response, we recorded the responses of V2 neurons in awake, fixating monkeys while presenting a diverse set of static shape stimuli within the classical receptive field. We analyzed the time course of various measures of responsiveness and stimulus-related response modulation at the level of individual cells and of the population. For a majority of V2 cells, the response modulation was maximal during the initial transient response (40-80 ms after stimulus onset). During the same period, the population response was relatively correlated, in that V2 cells tended to respond similarly to specific subsets of stimuli. Over the ensuing 80-100 ms, the signal-to-noise ratio of individual cells generally declined, but to a lesser degree than the evoked-response rate during the corresponding time bins, and the response profiles became decorrelated for many individual cells. Concomitantly, the population response became substantially decorrelated. Our results indicate that the information about stimulus shape evolves dynamically and relatively rapidly in V2 during static visual stimulation in ways that may contribute to form discrimination.

Animals↗
PubMed2004

Surface-based approaches to spatial localization and registration in primate cerebral cortex.

Explicit surface reconstructions provide invaluable substrates for visualizing and analyzing the complex convolutions of cerebral cortex. This report illustrates the utility of surface-based atlases of human and macaque monkey for representing many aspects of cortical organization and function. These include a variety of cortical partitioning schemes plus an open-ended collection of complex activation patterns obtained from fMRI studies. Surface-based registration from one hemisphere to an atlas provides powerful approach to (i) objectively and quantitatively representing both the consistencies and the variability of the pattern of convolutions and the patterns of functional activation from any given task; and (ii) making comparisons across species and evaluating candidate homologies between cortical areas or functionally delineated regions.

Animals↗
PubMed2003

Stereopsis activates V3A and caudal intraparietal areas in macaques and humans.

Stereopsis, the perception of depth from small differences between the images in the two eyes, provides a rich model for investigating the cortical construction of surfaces and space. Although disparity-tuned cells have been found in a large number of areas in macaque visual cortex, stereoscopic processing in these areas has never been systematically compared using the same stimuli and analysis methods. In order to examine the global architecture of stereoscopic processing in primate visual cortex, we studied fMRI activity in alert, fixating human and macaque subjects. In macaques, we found strongest activation to near/far compared to zero disparity in areas V3, V3A, and CIPS. In humans, we found strongest activation to the same stimuli in areas V3A, V7, the V4d topolog (V4d-topo), and a caudal parietal disparity region (CPDR). Thus, in both primate species a small cluster of areas at the parieto-occipital junction appears to be specialized for stereopsis.

Animals↗
PubMed2003

Functional organization of human intraparietal and frontal cortex for attending, looking, and pointing.

We studied the functional organization of human posterior parietal and frontal cortex using functional magnetic resonance imaging (fMRI) to map preparatory signals for attending, looking, and pointing to a peripheral visual location. The human frontal eye field and two separate regions in the intraparietal sulcus were similarly recruited in all conditions, suggesting an attentional role that generalizes across response effectors. However, the preparation of a pointing movement selectively activated a different group of regions, suggesting a stronger role in motor planning. These regions were lateralized to the left hemisphere, activated by preparation of movements of either hand, and included the inferior and superior parietal lobule, precuneus, and posterior superior temporal sulcus, plus the dorsal premotor and anterior cingulate cortex anteriorly. Surface-based registration of macaque cortical areas onto the map of fMRI responses suggests a relatively good spatial correspondence between human and macaque parietal areas. In contrast, large interspecies differences were noted in the topography of frontal areas.

Animals↗
PubMed2003

Persistence and brain circuitry.

The orbitofrontal and adjacent medial prefrontal cortex may play an important role in normal social functioning and affect modulation. Recent anatomical studies of this area of the prefrontal cortex have demonstrated a striking correspondence of fine-grained architectonic partitioning schemes in humans and nonhuman primates. This finding allows neurophysiological recording and anatomical connectivity data in animals to be considered together with functional imaging data and lesion studies in humans. In a functional MRI study, we show that individual differences in Persistence, a dimensional trait assessed with a seven-factor personality model, may be linked to specific areas in the lateral orbital and medial prefrontal cortex and the ventral striatum. These areas are part of an anatomical circuit that has been defined in nonhuman primates and has been implicated in functions related to behavioral persistence. These findings represent a fresh approach to linking normal individual differences in personality and behavior to specific neuronal structures and subsystems.

Adult↗
PubMed2002

Windows on the brain: the emerging role of atlases and databases in neuroscience.

Brain atlases and associated databases have great potential as gateways for navigating, accessing, and visualizing a wide range of neuroscientific data. Recent progress towards realizing this potential includes the establishment of probabilistic atlases, surface-based atlases and associated databases, combined with improvements in visualization capabilities and internet access.

Animals↗
PubMed2002

Surface-based atlases of cerebellar cortex in the human, macaque, and mouse.

This study describes surface reconstructions and associated flat maps that represent the highly convoluted shape of cerebellar cortex in three species: human, macaque, and mouse. The reconstructions were based on high-resolution structural MRI data obtained from other laboratories. The surface areas determined for the fiducial reconstructions are about 600 cm(2) for the human, 60 cm(2) for the macaque, and 0.8 cm(2) for the mouse. As expected from the ribbon-like pattern of cerebellar folding, the cerebellar flat maps are elongated along the axis parallel to the midline. However, the degree of elongation varies markedly across species. The macaque flat map is many times longer than its mean width, whereas the mouse flat map is only slightly elongated and the human map is intermediate in its aspect ratio. These cerebellar atlases, along with associated software for visualization and for mapping experimental data onto the atlas, are freely available to the neuroscience community (see http:/brainmap.wustl.edu).

Animals↗
PubMed2002

Scene segmentation and attention in primate cortical areas V1 and V2.

The responses of many neurons in primary visual cortex are modulated by stimuli outside the classical receptive field in ways that may contribute to integrative processes like scene segmentation. To explore this issue, single-unit neuronal responses were recorded in monkey cortical areas V1 and V2 to visual stimuli containing either a figure or a background pattern over the receptive field. Figures were defined either by orientation contrast or by illusory contours. In all conditions, the stimulation over the RF and its nearby surround was identical. Both figure types enhanced the average population response in V1 and V2. For orientation contrast figures, enhancement averaged 50% in V2 and 30% in V1; for illusory contour figures, the enhancement averaged 24% in V2 and 18% in V1. These differences were statistically significant for figure type but not for visual area. In V2, the latency of enhancement to illusory contour-defined figures was longer than that to orientation-defined figures. Neuronal responses were recorded while the monkey performed a directed-attention task. Enhancement to both figure types was observed even when attention was directed away from the figure. Attention slightly enhanced responses in V2, independent of figure type, but did not affect responses in V1. There was no discernible effect of attention on background firing rate in either V1 or V2. These results suggest that scene segmentation is a distributed process, in which neuronal signals at successive stages of the visual hierarchy and over time increasingly reflect the global structure of the image. This process occurs independent of directed visual attention.

Animals↗