scholarly journals Geometry and Geodesy on the Primary Visual Cortex as a Surface of Revolution

2020 ◽  
Vol 25 (4) ◽  
pp. 64
Author(s):  
Lorenzo G. Resca ◽  
Nicholas A. Mecholsky
Keyword(s):  
Differential Geometry ◽  
Visual Cortex ◽  
Visual Field ◽  
Eye Movement ◽  
Primary Visual Cortex ◽  
Three Dimensional ◽  
Dimensional Euclidean Space ◽  
Surface Of Revolution ◽  
Magnification Factors ◽  
Cortical Magnification

Biological mapping of the visual field from the eye retina to the primary visual cortex, also known as occipital area V1, is central to vision and eye movement phenomena and research. That mapping is critically dependent on the existence of cortical magnification factors. Once unfolded, V1 has a convex three-dimensional shape, which can be mathematically modeled as a surface of revolution embedded in three-dimensional Euclidean space. Thus, we solve the problem of differential geometry and geodesy for the mapping of the visual field to V1, involving both isotropic and non-isotropic cortical magnification factors of a most general form. We provide illustrations of our technique and results that apply to V1 surfaces with curve profiles relevant to vision research in general and to visual phenomena such as ‘crowding’ effects and eye movement guidance in particular. From a mathematical perspective, we also find intriguing and unexpected differential geometry properties of V1 surfaces, discovering that geodesic orbits have alternative prograde and retrograde characteristics, depending on the interplay between local curvature and global topology.

scholarly journals Morphological and Physiological Characterization of Layer VI Corticofugal Neurons of Mouse Primary Visual Cortex

2003 ◽  
Vol 89 (5) ◽  
pp. 2854-2867 ◽  
Author(s):  
Joshua C. Brumberg ◽  
Farid Hamzei-Sichani ◽  
Rafael Yuste
Keyword(s):  
Visual Cortex ◽  
Primary Visual Cortex ◽  
Action Potentials ◽  
Three Dimensional ◽  
Cell Types ◽  
Dorsal Lateral Geniculate Nucleus ◽  
Morphological Properties ◽  
Feedback Connection ◽  
Physiological Characterization ◽  
Layer Vi

Layer VI is the origin of the massive feedback connection from the cortex to the thalamus, yet its complement of cell types and their connections is poorly understood. The physiological and morphological properties of corticofugal neurons of layer VI of mouse primary visual cortex were investigated in slices loaded with the Ca2+indicator fura-2AM. To identify corticofugal neurons, electrical stimulation of the white matter (WM) was done in conjunction with calcium imaging to detect neurons that responded with changes in intracellular Ca2+ concentrations in response to the stimulation. Subsequent whole cell recordings confirmed that they discharged antidromic action potentials after WM stimulation. Antidromically activated neurons were more excitable and had different spiking properties than neighboring nonantidromic neurons, although both groups had similar input resistances. Furthermore, antidromic neurons possessed narrower action potentials and smaller afterhyperpolarizations. Additionally, three-dimensional reconstructions indicated that antidromically activated neurons had a distinct morphology with longer apical dendrites and fewer nonprimary dendrites than nonantidromic cells. To identify the antidromic neurons, rhodamine microspheres were injected into the dorsal lateral geniculate nucleus of the thalamus and allowed to retrogradely transport back to the somata of the layer VI cortico-geniculate neurons. Physiological and anatomical analysis indicated that most antidromic neurons were likely to be cortico-geniculate neurons. Our results show that cortico-thalamic neurons represent a specific functional and morphological class of layer VI neurons.

scholarly journals Cortical reorganization of the visual system in post-stroke hemianopia studied with fMRI

Stroke ◽  
2001 ◽  
Vol 32 (suppl_1) ◽  
pp. 334-334
Author(s):  
Gereon Nelles ◽  
Guido Widmann ◽  
Joachim Esser ◽  
Anette Meistrowitz ◽  
Johannes Weber ◽  
...  
Keyword(s):  
Visual Cortex ◽  
Visual Field ◽  
Visual System ◽  
Primary Visual Cortex ◽  
Visual Stimuli ◽  
Checkerboard Pattern ◽  
Partial Recovery ◽  
Area 18 ◽  
Area 19 ◽  
Stimulation Of

102 Introduction: Restitution of unilateral visual field defects following occipital cortex lesions occurs rarely. Partial recovery, however, can be observed in patients with incomplete lesion of the visual cortex. Our objective was to study the neuroplastic changes in the visual system that underlie such recovery. Methods and Results: Six patients with a left PCA-territory cortical stroke and 6 healthy control subjects were studied during rest and during visual stimulation using a 1.5 T fMRI with a 40 mT gradient. Visual stimuli were projected with a laptop computer onto a 154 x 115 cm screen, placed 90 cm in front of the gantry. Subjects were asked to fixate a red point in the center of the screen during both conditions. During stimulation, a black-and-white checkerboard pattern reversal was presented in each hemifield. For each side, 120 volumes of 48 contiguous axial fMRI images were obtained during rest and during hemifield stimulation in alternating order (60 volumes for each condition). Significant differences of rCBF between stimulation and rest were assessed as group analyses using statistical parametric mapping (SPM 99; p<0.01, corrected for multiple comparison). In controls, strong increases of rCBF (Z=7.6) occurred in the contralateral primary visual cortex V1 (area 17) and in V3a (area 18) and V5 (area 19). No differences were found between the right and left side in controls. During stimulation of the unaffected (left) visual field in hemianopic patients, activation occurred in contralateral V1, but the strongest increases of rCBF (Z>10) were seen in contralateral V3a (area 18) and V5 (area 19). During stimulation of the hemianopic (right) visual field, no activation was found in the primary visual cortex of either hemisphere. The most significant activation (Z=9.2) was seen in the ipsilateral V3a and V5 areas, and contralateral (left) V3a. Conclusions: Partial recovery from hemianopia is associated with strong ipsilateral activation of the visual system. Processing of visual stimuli in the hemianopic side spares the primary visual cortex and may involve recruitment of neurons in ipsilateral (contralesional) areas V3a and V5.

scholarly journals Disparity processing in primary visual cortex

2016 ◽  
Vol 371 (1697) ◽  
pp. 20150255 ◽  
Author(s):  
Sid Henriksen ◽  
Seiji Tanabe ◽  
Bruce Cumming
Keyword(s):  
Visual Cortex ◽  
Primary Visual Cortex ◽  
Striate Cortex ◽  
Three Dimensional ◽  
Empirical Support ◽  
Energy Model ◽  
Correspondence Problem ◽  
Stereo Correspondence ◽  
V1 Neurons ◽  
The Right

The first step in binocular stereopsis is to match features on the left retina with the correct features on the right retina, discarding ‘false’ matches. The physiological processing of these signals starts in the primary visual cortex, where the binocular energy model has been a powerful framework for understanding the underlying computation. For this reason, it is often used when thinking about how binocular matching might be performed beyond striate cortex. But this step depends critically on the accuracy of the model, and real V1 neurons show several properties that suggest they may be less sensitive to false matches than the energy model predicts. Several recent studies provide empirical support for an extended version of the energy model, in which the same principles are used, but the responses of single neurons are described as the sum of several subunits, each of which follows the principles of the energy model. These studies have significantly improved our understanding of the role played by striate cortex in the stereo correspondence problem. This article is part of the themed issue ‘Vision in our three-dimensional world’.

scholarly journals Near-optimal combination of disparity across a log-polar scaled visual field

2019 ◽  
Author(s):  
Guido Maiello ◽  
Manuela Chessa ◽  
Peter J. Bex ◽  
Fabio Solari
Keyword(s):  
Visual Cortex ◽  
Visual Field ◽  
Visual System ◽  
Primary Visual Cortex ◽  
Depth Perception ◽  
Binocular Disparity ◽  
Spatial Scales ◽  
Visual Input ◽  
Depth Information ◽  
Central Vision

AbstractThe human visual system is foveated: we can see fine spatial details in central vision, whereas resolution is poor in our peripheral visual field, and this loss of resolution follows an approximately logarithmic decrease. Additionally, our brain organizes visual input in polar coordinates. Therefore, the image projection occurring between retina and primary visual cortex can be mathematically described by the log-polar transform. Here, we test and model how this space-variant visual processing affects how we process binocular disparity, a key component of human depth perception. We observe that the fovea preferentially processes disparities at fine spatial scales, whereas the visual periphery is tuned for coarse spatial scales, in line with the naturally occurring distributions of depths and disparities in the real-world. We further show that the visual field integrates disparity information across the visual field, in a near-optimal fashion. We develop a foveated, log-polar model that mimics the processing of depth information in primary visual cortex and that can process disparity directly in the cortical domain representation. This model takes real images as input and recreates the observed topography of disparity sensitivity in man. Our findings support the notion that our foveated, binocular visual system has been moulded by the statistics of our visual environment.Author summaryWe investigate how humans perceive depth from binocular disparity at different spatial scales and across different regions of the visual field. We show that small changes in disparity-defined depth are detected best in central vision, whereas peripheral vision best captures the coarser structure of the environment. We also demonstrate that depth information extracted from different regions of the visual field is combined into a unified depth percept. We then construct an image-computable model of disparity processing that takes into account how our brain organizes the visual input at our retinae. The model operates directly in cortical image space, and neatly accounts for human depth perception across the visual field.

scholarly journals Differential geometry of intersection curve of two surfaces

2009 ◽  
Vol 50 ◽  
Author(s):  
Kazimieras Navickis
Keyword(s):  
Differential Geometry ◽  
Euclidean Space ◽  
Three Dimensional ◽  
Dimensional Euclidean Space ◽  
Intersection Curve ◽  
Curvature And Torsion

In this this article the differential geometry of intersection curve of two surfaces in the three dimensional euclidean space is considered.In case, curvature and torsion formulas for such curve are defined.

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