scholarly journals Novel neural circuit mechanism for visual edge detection

2015 ◽  
Vol 112 (3) ◽  
pp. 875-880 ◽  
Author(s):  
Charles F. Stevens
Keyword(s):  
Visual Cortex ◽  
Edge Detection ◽  
Visual Information ◽  
Neural Circuit ◽  
Frequency Tuning ◽  
Orientation Tuning ◽  
Image Patch ◽  
Small Parts ◽  
The Brain ◽  
Slope Orientation

The primary visual cortex is organized in a way that assigns a specific collection of neurons the job of providing the rest of the brain with all of the information it needs about each small part of the image present on the retina: Neighboring patches of the visual cortex provide the information about neighboring patches of the visual world. Each one of these cortical patches—often identified as a “pinwheel”—contains thousands of neurons, and its corresponding image patch is centered on a particular location in the retina. For stimuli within their image patch, neurons respond selectively to lines or edges with a particular slope (orientation tuning) and to regions of the patch of different sizes (known as spatial frequency tuning). The same number of neurons is devoted to reporting each possible slope (orientation). For the cells that cover different-sized regions of their image patch, however, the number of neurons assigned depends strongly on their preferred region size. Only a few neurons report on large and small parts of the image patch, but many neurons report visual information from medium-sized areas. I show here that having different numbers of neurons responsible for image regions of different sizes actually carries out a computation: Edges in the image patch are extracted. I also explain how this edge-detection computation is done.

scholarly journals Blindsight and Unconscious Vision: What They Teach Us about the Human Visual System

2016 ◽  
Vol 23 (5) ◽  
pp. 529-541 ◽  
Author(s):  
Sara Ajina ◽  
Holly Bridge
Keyword(s):  
Visual Cortex ◽  
Visual System ◽  
Primary Visual Cortex ◽  
Neural Activity ◽  
Human Visual System ◽  
Visual Information ◽  
Visual Loss ◽  
Physiological Conditions ◽  
The World ◽  
The Brain

Damage to the primary visual cortex removes the major input from the eyes to the brain, causing significant visual loss as patients are unable to perceive the side of the world contralateral to the damage. Some patients, however, retain the ability to detect visual information within this blind region; this is known as blindsight. By studying the visual pathways that underlie this residual vision in patients, we can uncover additional aspects of the human visual system that likely contribute to normal visual function but cannot be revealed under physiological conditions. In this review, we discuss the residual abilities and neural activity that have been described in blindsight and the implications of these findings for understanding the intact system.

Brain Basis of Blindsight

2020 ◽  
Author(s):  
Holly Bridge
Keyword(s):  
Visual Cortex ◽  
Primary Visual Cortex ◽  
Visual Information ◽  
Diffusion Imaging ◽  
Visual Stimuli ◽  
Cortical Blindness ◽  
Functional Brain Imaging ◽  
Rehabilitation Programs ◽  
The World ◽  
The Brain

The sensation of vision arises from the detection of photons of light at the eye, but in order to produce the percept of the world, extensive regions of the brain are required to process the visual information. The majority of information entering the brain via the optic nerve from the eye projects via the lateral geniculate nucleus (LGN) of the thalamus to the primary visual cortex, the largest visual area, having been reorganized such that one side of the brain represents one side of the world. Damage to the primary visual cortex in one hemisphere therefore leads to a loss of conscious vision on the opposite side of the world, known as hemianopia. Despite this cortical blindness, many patients are still able to detect visual stimuli that are presented in the blind region if forced to guess whether a stimulus is present or absent. This is known as “blindsight.” For patients to gain any information (conscious or unconscious) about the visual world, the input from the eye must be processed by the brain. Indeed, there is considerable evidence from functional brain imaging that several visual areas continue to respond to visual stimuli presented within the blind region, even when the patient is unaware of the stimulus. Furthermore, the use of diffusion imaging allows the microstructure of white matter pathways within the visual system to be examined to see whether they are damaged or intact. By comparing patients who have hemianopia with and without blindsight it is possible to determine the pathways that are linked to blindsight function. Through understanding the brain areas and pathways that underlie blindsight in humans and non-human primates, the aim is to use modern neuroscience to guide rehabilitation programs for use after stroke.

Mammalian Visual System Organization

2017 ◽  
Author(s):  
Farran Briggs
Keyword(s):  
Visual Cortex ◽  
Visual System ◽  
Visual Information ◽  
Contextual Information ◽  
Sensory Information ◽  
Visual Image ◽  
Brain Structures ◽  
Object Representations ◽  
System A ◽  
The Brain

Many mammals, including humans, rely primarily on vision to sense the environment. While a large proportion of the brain is devoted to vision in highly visual animals, there are not enough neurons in the visual system to support a neuron-per-object look-up table. Instead, visual animals evolved ways to rapidly and dynamically encode an enormous diversity of visual information using minimal numbers of neurons (merely hundreds of millions of neurons and billions of connections!). In the mammalian visual system, a visual image is essentially broken down into simple elements that are reconstructed through a series of processing stages, most of which occur beneath consciousness. Importantly, visual information processing is not simply a serial progression along the hierarchy of visual brain structures (e.g., retina to visual thalamus to primary visual cortex to secondary visual cortex, etc.). Instead, connections within and between visual brain structures exist in all possible directions: feedforward, feedback, and lateral. Additionally, many mammalian visual systems are organized into parallel channels, presumably to enable efficient processing of information about different and important features in the visual environment (e.g., color, motion). The overall operations of the mammalian visual system are to: (1) combine unique groups of feature detectors in order to generate object representations and (2) integrate visual sensory information with cognitive and contextual information from the rest of the brain. Together, these operations enable individuals to perceive, plan, and act within their environment.

scholarly journals Dynamics of spatial frequency tuning in mouse visual cortex

2012 ◽  
Vol 107 (11) ◽  
pp. 2937-2949 ◽  
Author(s):  
Samme Vreysen ◽  
Bin Zhang ◽  
Yuzo M. Chino ◽  
Lutgarde Arckens ◽  
Gert Van den Bergh
Keyword(s):  
Visual Cortex ◽  
Spatial Frequency ◽  
Visual Information ◽  
Frequency Tuning ◽  
Neuronal Response ◽  
Correlation Technique ◽  
Low Frequencies ◽  
Temporal Shift ◽  
Spatial Frequency Tuning ◽  
Spatial Frequencies

Neuronal spatial frequency tuning in primary visual cortex (V1) substantially changes over time. In both primates and cats, a shift of the neuron's preferred spatial frequency has been observed from low frequencies early in the response to higher frequencies later in the response. In most cases, this shift is accompanied by a decreased tuning bandwidth. Recently, the mouse has gained attention as a suitable animal model to study the basic mechanisms of visual information processing, demonstrating similarities in basic neuronal response properties between rodents and highly visual mammals. Here we report the results of extracellular single-unit recordings in the anesthetized mouse where we analyzed the dynamics of spatial frequency tuning in V1 and the lateromedial area LM within the lateral extrastriate area V2L. We used a reverse-correlation technique to demonstrate that, as in monkeys and cats, the preferred spatial frequency of mouse V1 neurons shifted from low to higher frequencies later in the response. However, this was not correlated with a clear selectivity increase or enhanced suppression of responses to low spatial frequencies. These results suggest that the neuronal connections responsible for the temporal shift in spatial frequency tuning may considerably differ between mice and monkeys.

Neural Plasticity in Amblyopia

2021 ◽  
Author(s):  
Benjamin Thompson
Keyword(s):  
Visual Cortex ◽  
Neural Plasticity ◽  
Visual Information ◽  
Randomized Clinical Trials ◽  
Adult Brain ◽  
Abnormal Development ◽  
Sensitive Period ◽  
Early 21St Century ◽  
Functional Changes ◽  
The Brain

Early in life, the brain has a substantial capacity for change, often referred to as neuroplasticity. Disrupted visual input to the brain during an early “critical” or “sensitive period” of heightened neuroplasticity induces structural and functional changes within neural systems and causes amblyopia, a sensory disorder associated with abnormal development of the brain areas involved in perception. Amblyopia impairs a broad range of visual, multisensory, and motor functions, and recovery from amblyopia requires a substantial change in visual information processing within the brain. Therefore, not only is amblyopia caused by an interaction between visual experience and heightened neuroplasticity, recovery from amblyopia also requires significant neuroplastic change within the brain. A number of evidence-based treatments are available for young children with amblyopia whose brains are still rapidly developing and have a correspondingly high level of neuroplasticity. However, adults with amblyopia are often left untreated because of the idea that the adult brain no longer has sufficient neuroplasticity to relearn how to process visual information. In the early 21st century, it became clear that this idea was not correct. A number of interventions that can enhance neuroplasticity in the mature visual cortex have been identified using animal models of amblyopia and are now being translated into human studies. Other promising techniques for enhancing visual cortex neuroplasticity have emerged from studies of adult humans with amblyopia. Examples of interventions that may improve vision in adult amblyopia include refractive correction, patching of the amblyopic eye (reverse patching), monocular and binocular perceptual learning, noninvasive brain stimulation, systemic drugs, and exercise. The next important stage of research within this field will be to conduct fully controlled randomized clinical trials to assess which, if any, of these interventions can be translated into a mainstream treatment for amblyopia in adulthood.

scholarly journals Influence of Contrast on Orientation and Temporal Frequency Tuning in Ferret Primary Visual Cortex

2004 ◽  
Vol 91 (6) ◽  
pp. 2797-2808 ◽  
Author(s):  
Henry J. Alitto ◽  
W. Martin Usrey
Keyword(s):  
Visual Cortex ◽  
Primary Visual Cortex ◽  
Cortical Neurons ◽  
Frequency Tuning ◽  
Temporal Frequency ◽  
Orientation Tuning ◽  
Visual Response ◽  
Stimulus Contrast ◽  
Tuning Curves ◽  
Simple And Complex Cells

Neurons in primary visual cortex are highly sensitive to the contrast, orientation, and temporal frequency of a visual stimulus. These three stimulus properties can be varied independently of one another, raising the question of how they interact to influence neuronal responses. We recorded from individual neurons in ferret primary visual cortex to determine the influence of stimulus contrast on orientation tuning, temporal-frequency tuning, and latency to visual response. Results show that orientation-tuning bandwidth is not affected by contrast level. Thus neurons in ferret visual cortex display contrast-invariant orientation tuning. Stimulus contrast does, however, influence the structure of orientation-tuning curves as measures of circular variance vary inversely with contrast for both simple and complex cells. This change in circular variance depends, in part, on a contrast-dependent change in the ratio of null to preferred orientation responses. Stimulus contrast also has an influence on the temporal-frequency tuning of cortical neurons. Both simple and complex cells display a contrast-dependent rightward shift in their temporal frequency-tuning curves that results in an increase in the highest temporal frequency needed to produce a half-maximum response (TF50). Results show that the degree of the contrast-dependent increase in TF50 is similar for cortical neurons and neurons in the lateral geniculate nucleus (LGN) and indicate that subcortical mechanisms likely play a major role in establishing the degree of effect displayed by downstream neurons. Finally, results show that LGN and cortical neurons experience a contrast-dependent phase advance in their visual response. This phase advance is most pronounced for cortical neurons indicating a role for both subcortical and cortical mechanisms.

scholarly journals Functional ultrasound imaging of the spreading activity following optogenetic stimulation of the rat visual cortex

2021 ◽  
Author(s):  
M. Provansal ◽  
G. Labernede ◽  
C. Joffrois ◽  
A. Rizkallah ◽  
R. Goulet ◽  
...  
Keyword(s):  
Visual Cortex ◽  
Ultrasound Imaging ◽  
Visual Information ◽  
Brain Response ◽  
Information Process ◽  
Optogenetic Stimulation ◽  
Deep Layers ◽  
Sight Restoration ◽  
The Brain ◽  
Stimulation Of

Optogenetic stimulation of the primary visual cortex (V1) is a promising therapy for sight restoration, but it remains unclear what total cerebral volume is activated after surface stimulation. In this study, we expressed the red-shifted opsin ChrimsonR in excitatory neurons within V1 in rats, and used the fine spatial resolution provided by functional ultrasound imaging (fUS) over the whole depth of the brain to investigate the brain response to focal surface stimulation. We observed optogenetic activation of a high proportion of the volume of V1. Extracellular recordings confirmed the neuronal origin of this activation. Moreover, neuronal responses were even located in deep layers under conditions of low irradiance, spreading to the LGN and V2, consistent with a normal visual information process. This study paves the way for the use of optogenetics for cortical therapies, and highlights the value of coupling fUS with optogenetics.

Functional Organisation of Human Visual Cortex Revealed by fMRI

Perception ◽  
1997 ◽  
Vol 26 (1_suppl) ◽  
pp. 9-9 ◽  
Author(s):  
R B H Tootell ◽  
A M Dale ◽  
N Hadjikhani ◽  
A K Liu ◽  
S Marrett ◽  
...  
Keyword(s):  
Visual Cortex ◽  
Visual Information ◽  
Visual Stimulation ◽  
Frequency Tuning ◽  
Human Subjects ◽  
Planar Imaging ◽  
Posterior Cortex ◽  
Human Visual Cortex ◽  
Wide Range ◽  
Functional Organisation

Until recently, comparatively little was known about the functional organisation of human visual cortex. Functional magnetic resonance imaging (fMRI), in conjunction with cortical flattening techniques and psychophysically relevant visual stimulation, has greatly clarified human visual-information processing. To date, we have completed cortical surface reconstructions (flattening), coupled with a wide range of visual stimulus testing, on 28 normal human subjects. Visual activation was acquired on a 1.5 T GE MR scanner with ANMR echo-planar imaging, with the use of a custom, bilateral, quadrature surface coil covering posterior cortex. Approximately ten visual cortical areas can now be functionally localised each with unique functional and topographical properties. The most well-defined areas are: V1, V2, V3, VP, V3A, V4v, MT, SPO, and perhaps MSTd. Most of the properties in these human areas are similar to those reported in presumably homologous areas of macaque, but distinctive species differences also appear to exist, notably in V3/VP, V4v, and V3A. Human areas showing prominant motion-selectivity include V3A, MT/MSTd, SPO, and a small area near the superior sylvian fissure. Retinotopic areas include V1, V2, V3, VP, V4v, and V3A. The human cortical magnification factor appears higher towards the fovea than in macaque, but, like macaque, preferred spatial frequency tuning varies inversely with eccentricity in all retinotopic areas in which sinusoidal gratings are effective stimuli.

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