scholarly journals Compressive spatial summation in human visual cortex

2013 ◽  
Vol 110 (2) ◽  
pp. 481-494 ◽  
Author(s):  
Kendrick N. Kay ◽  
Jonathan Winawer ◽  
Aviv Mezer ◽  
Brian A. Wandell
Keyword(s):  
Visual Cortex ◽  
Visual Field ◽  
Object Representation ◽  
Spatial Summation ◽  
Blood Oxygenation ◽  
Population Responses ◽  
Visual Areas ◽  
Oxygenation Level ◽  
Restricted Region ◽  
Extrastriate Areas

Neurons within a small (a few cubic millimeters) region of visual cortex respond to stimuli within a restricted region of the visual field. Previous studies have characterized the population response of such neurons using a model that sums contrast linearly across the visual field. In this study, we tested linear spatial summation of population responses using blood oxygenation level-dependent (BOLD) functional MRI. We measured BOLD responses to a systematic set of contrast patterns and discovered systematic deviation from linearity: the data are more accurately explained by a model in which a compressive static nonlinearity is applied after linear spatial summation. We found that the nonlinearity is present in early visual areas (e.g., V1, V2) and grows more pronounced in relatively anterior extrastriate areas (e.g., LO-2, VO-2). We then analyzed the effect of compressive spatial summation in terms of changes in the position and size of a viewed object. Compressive spatial summation is consistent with tolerance to changes in position and size, an important characteristic of object representation.

scholarly journals Independence of Anticipatory Signals for Spatial Attention From Number of Nontarget Stimuli in the Visual Field

2008 ◽  
Vol 100 (2) ◽  
pp. 829-838 ◽  
Author(s):  
C. Sestieri ◽  
C. M. Sylvester ◽  
A. I. Jack ◽  
G. d'Avossa ◽  
G. L. Shulman ◽  
...  
Keyword(s):  
Visual Cortex ◽  
Visual Field ◽  
Spatial Attention ◽  
Visual Stimulation ◽  
Blood Oxygenation ◽  
Bold Signal ◽  
Signal Modulation ◽  
Low Contrast ◽  
Upper Visual Field ◽  
Oxygenation Level

Covertly attending to a location modulates the activity of visual areas even in the absence of visual stimulation. These effects are widespread, being found in the cortical representations of both attended and unattended portions of the visual field. It is not clear, however, whether preparatory modulations depend on subjects' expectation regarding the presence of additional nontarget stimuli in the visual field. Here, we asked subjects to endogenously direct attention to a peripheral location in the upper visual field, to identify the orientation of a low-contrast target stimulus, and we manipulated the number and behavioral relevance of other low-contrast nontarget stimuli in the visual field. Anticipatory (i.e., prestimulus) blood oxygenation level–dependent (BOLD) signal increments in visual cortex were strongest at the contralateral attended location, whereas signal decrements were strongest at the unattended mirror-opposite ipsilateral location/region of visual cortex. Importantly, these strong anticipatory decrements were not related to the presence/absence of nontarget low-contrast stimuli and did not correlate with either weaker target-evoked responses or worse performance. Second, the presence of other low-contrast stimuli in the visual field, even when potential targets, did not modify the anticipatory signal modulation either at target or nontarget locations. We conclude that the topography of spatial attention–related anticipatory BOLD signal modulation across visual cortex, specifically decrements at unattended locations, is mainly determined by processes at the cued location and not by the number or behavioral relevance of distant low-contrast nontarget stimuli elsewhere in the visual field.

scholarly journals Myelin densities in retinotopically defined dorsal visual areas of the macaque

2021 ◽  
Author(s):  
Xiaolian Li ◽  
Qi Zhu ◽  
Wim Vanduffel
Keyword(s):  
Visual Cortex ◽  
Visual Field ◽  
Cortical Thickness ◽  
New World Monkeys ◽  
Isotropic Resolution ◽  
Density Mapping ◽  
Area V2 ◽  
Visual Areas ◽  
Density Results

AbstractThe visuotopic organization of dorsal visual cortex rostral to area V2 in primates has been a longstanding source of controversy. Using sub-millimeter phase-encoded retinotopic fMRI mapping, we recently provided evidence for a surprisingly similar visuotopic organization in dorsal visual cortex of macaques compared to previously published maps in New world monkeys (Zhu and Vanduffel, Proc Natl Acad Sci USA 116:2306–2311, 2019). Although individual quadrant representations could be robustly delineated in that study, their grouping into hemifield representations remains a major challenge. Here, we combined in-vivo high-resolution myelin density mapping based on MR imaging (400 µm isotropic resolution) with fine-grained retinotopic fMRI to quantitatively compare myelin densities across retinotopically defined visual areas in macaques. Complementing previously documented differences in populational receptive-field (pRF) size and visual field signs, myelin densities of both quadrants of the dorsolateral posterior area (DLP) and area V3A are significantly different compared to dorsal and ventral area V3. Moreover, no differences in myelin density were observed between the two matching quadrants belonging to areas DLP, V3A, V1, V2 and V4, respectively. This was not the case, however, for the dorsal and ventral quadrants of area V3, which showed significant differences in MR-defined myelin densities, corroborating evidence of previous myelin staining studies. Interestingly, the pRF sizes and visual field signs of both quadrant representations in V3 are not different. Although myelin density correlates with curvature and anticorrelates with cortical thickness when measured across the entire cortex, exactly as in humans, the myelin density results in the visual areas cannot be explained by variability in cortical thickness and curvature between these areas. The present myelin density results largely support our previous model to group the two quadrants of DLP and V3A, rather than grouping DLP- with V3v into a single area VLP, or V3d with V3A+ into DM.

scholarly journals Eccentricity Mapping of the Human Visual Cortex to Evaluate Temporal Dynamics of Functional T1ρ Mapping

2015 ◽  
Vol 35 (7) ◽  
pp. 1213-1219 ◽  
Author(s):  
Hye-Young Heo ◽  
John A Wemmie ◽  
Casey P Johnson ◽  
Daniel R Thedens ◽  
Vincent A Magnotta
Keyword(s):  
Blood Flow ◽  
Visual Cortex ◽  
Temporal Dynamics ◽  
Occipital Cortex ◽  
Hemodynamic Response ◽  
Proton Exchange ◽  
Blood Oxygenation ◽  
Human Visual Cortex ◽  
Tissue Metabolism ◽  
Oxygenation Level

Recent experiments suggest that T1 relaxation in the rotating frame ( T1ρ) is sensitive to metabolism and can detect localized activity-dependent changes in the human visual cortex. Current functional magnetic resonance imaging (fMRI) methods have poor temporal resolution due to delays in the hemodynamic response resulting from neurovascular coupling. Because T1ρ is sensitive to factors that can be derived from tissue metabolism, such as pH and glucose concentration via proton exchange, we hypothesized that activity-evoked T1ρ changes in visual cortex may occur before the hemodynamic response measured by blood oxygenation level-dependent (BOLD) and arterial spin labeling (ASL) contrast. To test this hypothesis, functional imaging was performed using BOLD, and ASL in human participants viewing an expanding ring stimulus. We calculated eccentricity phase maps across the occipital cortex for each functional signal and compared the temporal dynamics of T1ρ versus BOLD and ASL. The results suggest that T1ρ changes precede changes in the two blood flow-dependent measures. These observations indicate that T1ρ detects a signal distinct from traditional fMRI contrast methods. In addition, these findings support previous evidence that T1ρ is sensitive to factors other than blood flow, volume, or oxygenation. Furthermore, they suggest that tissue metabolism may be driving activity-evoked T1ρ changes.

Pontine projection from striate and prestriate visual cortex in the macaque monkey: An anterograde study

1990 ◽  
Vol 4 (3) ◽  
pp. 205-216 ◽  
Author(s):  
W. Fries
Keyword(s):  
Visual Cortex ◽  
Visual Field ◽  
Striate Cortex ◽  
Macaque Monkey ◽  
Field Of View ◽  
Central Visual Field ◽  
Tracer Techniques ◽  
Visual Areas ◽  
Visual Cortical ◽  
Anterograde Tracer

AbstractThe projection from striate and prestriate visual cortex to the pontine nuclei has been studied in the macaque monkey by means of anterograde tracer techniques in order to assess the contribution of anatomically and functionally distinct visual cortical areas to the cortico-ponto-cerebellar loop. No projection to the pons was found from central or paracentral visual-field representations of V1 (striate cortex) or prestriate visual areas V2, and V4. Small patches of terminal labeling occurred after injections of tracer into more peripheral parts of V1, V2 and V3, and into V3A. The terminal fields were located most dorsolaterally in the anterior to middle third of the pons and were quite restricted in their rostro-caudal extent. Injections of V5, however, yielded substantial terminal labeling, stretching longitudinally throughout almost the entire pons. This projection could be demonstrated to arise from parts of V5 receiving input from central visual-field representations of striate cortex, whereas parts of V4 receiving similarly central visual-field input had no detectable projection to the pons. Its distribution may overlap to a large extent with the termination of tecto-pontine fibers and with the termination of fibers from visual areas in the medial bank (area V6 or P0) and lateral bank (area LIP) of the intraparietal sulcus, as well as from frontal eye fields (FEF). It appears that the main information relayed to the cerebellum by the visual corticopontine projection is related to movement in the field of view.

Blood oxygenation level-dependent (BOLD) total and extravascular signal changes and ΔR 2 * in human visual cortex at 1.5, 3.0 and 7.0 T

2010 ◽  
Vol 24 (1) ◽  
pp. 25-34 ◽  
Author(s):  
Manus J. Donahue ◽  
Hans Hoogduin ◽  
Peter C. M. van Zijl ◽  
Peter Jezzard ◽  
Peter R. Luijten ◽  
...  
Keyword(s):  
Visual Cortex ◽  
Blood Oxygenation Level Dependent ◽  
Blood Oxygenation ◽  
Human Visual Cortex ◽  
Blood Oxygenation Level ◽  
Oxygenation Level ◽  
Signal Changes

Effect of Luminance Contrast on BOLD fMRI Response in Human Primary Visual Areas

1998 ◽  
Vol 79 (4) ◽  
pp. 2204-2207 ◽  
Author(s):  
Bradley G. Goodyear ◽  
Ravi S. Menon
Keyword(s):  
Luminance Contrast ◽  
Blood Oxygenation ◽  
Planar Imaging ◽  
Bold Fmri ◽  
Activation Level ◽  
Red Led ◽  
Visual Areas ◽  
Oxygenation Level ◽  
Fmri Response ◽  
Image Pixels

Goodyear, Bradley G. and Ravi S. Menon. Effect of luminance contrast on BOLD fMRI response in human primary visual areas. J. Neurophysiol. 79: 2204–2207, 1998. In this study, we examined the effect of stimulus luminance contrast on blood-oxygenation-level-dependent (BOLD) functional magnetic resonance imaging within human visual cortex (V1 and extrastriate). Between experiments, the calibrated luminance of a single red LED covering 2° of the subject's visual field was changed relative to a constant background luminance. This stimulus provided a different foveal luminance contrast for each experiment. We used an echo planar imaging sequence to collect blood-oxygenation-sensitive images during and in the absence of the presented stimulus. Our results showed that within V1 there was an increase in the spatial extent of activation with increasing stimulus contrast, but no trend was seen within extrastriate. In both V1 and extrastriate, the local mean activation level for all activated image pixels remained constant with increasing luminance contrast. However, when we investigated activated pixels common to all luminance contrast levels, we found that there was an increase in the mean activation level within V1, but not within extrastriate. These results suggest that there is an increase in the activity of cells in V1 with increasing luminance contrast.

scholarly journals Dynamic metabolic changes in human visual cortex in regions with positive and negative blood oxygenation level-dependent response

2018 ◽  
Vol 39 (11) ◽  
pp. 2295-2307 ◽  
Author(s):  
Miguel Martínez-Maestro ◽  
Christian Labadie ◽  
Harald E Möller
Keyword(s):  
Visual Cortex ◽  
Tricarboxylic Acid Cycle ◽  
Blood Oxygenation Level Dependent ◽  
Blood Oxygenation ◽  
Metabolic Changes ◽  
Resonance Spectroscopy ◽  
Bold Response ◽  
Full Field ◽  
Blood Oxygenation Level ◽  
Oxygenation Level

Dynamic metabolic changes were investigated by functional magnetic resonance spectroscopy (fMRS) during sustained stimulation of human primary visual cortex. Two established paradigms, consisting of either a full-field or a small-circle flickering checkerboard, were employed to generate wide-spread areas of positive or negative blood oxygenation level-dependent (BOLD) responses, respectively. Compared to baseline, the glutamate concentration increased by 5.3% ( p = 0.007) during activation and decreased by −3.8% ( p = 0.017) during deactivation. These changes were positively correlated with the amplitude of the BOLD response ( R = 0.60, p = 0.002) and probably reflect changes of tricarboxylic acid cycle activity. During deactivation, the glucose concentration decreased by −7.9% ( p = 0.025) presumably suggesting increased consumption or reduced glucose supply. Other findings included an increased concentration of glutathione (4.2%, p = 0.023) during deactivation and a negative correlation of glutathione and BOLD signal changes ( R = −0.49, p = 0.012) as well as positive correlations of aspartate ( R = 0.44, p = 0.035) and N-acetylaspartylglutamate ( R = 0.42, p = 0.035) baseline concentrations with the BOLD response. It remains to be shown in future work if the observed effects on glutamate and glucose levels deviate from the assumption of a direct link between glucose utilization and regulation of blood flow or support previous suggestions that the hemodynamic response is mainly driven by feedforward release of vasoactive messengers.

scholarly journals Long-Term Memory Search across the Visual Brain

2012 ◽  
Vol 2012 ◽  
pp. 1-14 ◽  
Author(s):  
Milan Fedurco
Keyword(s):  
Visual Cortex ◽  
Visual Memory ◽  
Signal Transmission ◽  
Memory Search ◽  
Postsynaptic Membrane ◽  
Blood Oxygenation ◽  
Multisensory Perception ◽  
Long Term Memory ◽  
Oxygenation Level

Signal transmission from the human retina to visual cortex and connectivity of visual brain areas are relatively well understood. How specific visual perceptions transform into corresponding long-term memories remains unknown. Here, I will review recent Blood Oxygenation Level-Dependent functional Magnetic Resonance Imaging (BOLD fMRI) in humans together with molecular biology studies (animal models) aiming to understand how the retinal image gets transformed into so-called visual (retinotropic) maps. The broken object paradigm has been chosen in order to illustrate the complexity of multisensory perception of simple objects subject to visual —rather than semantic— type of memory encoding. The author explores how amygdala projections to the visual cortex affect the memory formation and proposes the choice of experimental techniques needed to explain our massive visual memory capacity. Maintenance of the visual long-term memories is suggested to require recycling of GluR2-containingα-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPAR) andβ2-adrenoreceptors at the postsynaptic membrane, which critically depends on the catalytic activity of the N-ethylmaleimide-sensitive factor (NSF) and protein kinase PKMζ.

Residual Vision in a Subject with Damaged Visual Cortex

1999 ◽  
Vol 11 (5) ◽  
pp. 502-510 ◽  
Author(s):  
Heinz Schärli ◽  
Alison M. Harman ◽  
John H. Hogben
Keyword(s):  
Visual Cortex ◽  
Visual Field ◽  
Target Stimulus ◽  
Striate Cortex ◽  
Light Flash ◽  
Black And White ◽  
Confidence Levels ◽  
Residual Vision ◽  
Visual Areas ◽  
The Subject

It is well known that a lesion in the optic radiation or striate cortex leads to blind visual regions in the retinotopically corresponding portion of the visual field. However, various studies show that some subjects still perceive certain stimuli even when presented in the “blind” visual field. Such subjects either perceive stimuli abnormally or only certain aspects of them (residual vision) or, in some cases, deny perception altogether even though visual performance can be shown to be above chance (blindsight). Research on monkeys has suggested a variety of parallel extrastriate visual pathways that could bypass the striate cortex and mediate residual vision or blindsight. In the present study, we investigated a subject with perimetrically blind visual areas caused by bilateral brain damage. Black and white stimuli were presented at many locations in the intact and affected areas of the visual field. The subject's task was to state, using confidence levels, whether the target stimulus was black or white. The results revealed an area in the “blind” visual field in which the subject perceived a light flash when the experimental black stimulus was presented. We hypothesize that a spared region in the visual cortex most likely accounts for these findings.

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