ABSTRACT. Aging often results in reduced visual acuity from changes in both the eye and neural circuits [1-4]. In normally aging subjects, primary visual cortex has been shown to have reduced responses to visual stimulation [5]. It is not known, however, to what extent aging affects visual field representations and population receptive sizes in human primary visual cortex. Here we use functional MRI (fMRI) and population receptive field (pRF) modeling [6] to measure angular and eccentric retinotopic representations and population receptive fields in primary visual cortex in healthy aging subjects ages 57 - 70 and in healthy young volunteers ages 24 - 36 (n = 9). Retinotopic stimuli consisted of black and white, drifting checkerboards comprising moving bars 11 deg in radius. Primary visual cortex (V1) was clearly identifiable along the calcarine sulcus in all hemispheres. There was a significant decrease in the surface area of V1 from 0 to 3 deg eccentricity in the aging subjects with respect to ...
Aging often results in reduced visual acuity from changes in both the eye and neural circuits [1-4]. In normally aging subjects, primary visual cortex has been shown to have reduced responses to visual stimulation [5]. It is not known, however, to what extent aging affects visual field repre-sentations and population receptive sizes in human primary visual cortex. Here we use func-tional MRI (fMRI) and population receptive field (pRF) modeling [6] to measure angular and ec-centric retinotopic representations and population receptive fields in primary visual cortex in healthy aging subjects ages 57 - 70 and in healthy young volunteers ages 24 - 36 (n = 9). Retinotopic stimuli consisted of black and white, drifting checkerboards comprising moving bars 11 deg in radius. Primary visual cortex (V1) was clearly identifiable along the calcarine sulcus in all hemispheres. There was a significant decrease in the surface area of V1 from 0 to 3 deg eccentricity in the aging subjects with respect to the young
The cerebral cortex changes throughout the lifespan, and the cortical grey matter in many brain regions becomes thinner with advancing age. Effects of aging on cortical thickness have been observed in many brain regions, including areas involved in basic perceptual functions such as processing visual inputs. An important property of early visual cortices is their topographic organization - the cortical structure of early visual areas forms a topographic map of retinal inputs. Primary visual cortex (V1) is considered to be the most basic cortical area in the visual processing hierarchy, and is topographically organized from posterior (central visual representation) to anterior (peripheral visual representation) along the calcarine sulcus. Some studies have reported strong age-dependent cortical thinning in portions of V1 that likely correspond to peripheral visual representations, while there is less evidence of substantial cortical thinning in central V1. However, the effect of aging on cortical
Through massively parallel computational simulations, we studied how a large network of simple neural elements (the RF-LISSOM model) could develop a functional organization similar to that of the primary visual cortex. It was found that starting from a tabula rasa state, the afferent and lateral connections in the network self-organized cooperatively and simultaneously through a common Hebbian mechanism, and produced receptive fields (RFs), orientation maps, and patterns of lateral connections that follow the receptive field organization. Second, we hypothesized that similar self-organizing mechanisms continue operating in the adult cortex, maintaining it in a continuously-adapting dynamic equilibrium with the input, and tested this hypothesis on the self-organized model. When the equilibrium was perturbed by a retinal scotoma, RFs expanded in size in a reversible fashion, matching recent neurobiological observations in the cat and psychophysical experiments in the human. Third, a possible ...
The simple-cell receptive field (RF) structure is an attractive and unique feature of the primary visual cortex, which is thought to reflect the circuitry principles governing orientation selectivity. Synaptic inputs underlying spike RFs are key to understanding mechanisms for neuronal processing. The well-known push-pull model, which is proposed to explain the synaptic mechanism under simple-cell RFs, predicts that in simple cells the spatially separated excitation and inhibition does not interact with each other and that simple inhibitory neurons exist in the primary visual cortex (V1). However, previous experimental results suggest that synaptic inhibition plays an important role in shaping RF properties in the visual cortex. The synaptic mechanisms underlying simple-cell RFs remain not well understood, partly due to difficulties in systematically studying functional properties of cortical inhibitory neurons and precisely measuring excitatory and inhibitory synaptic inputs in vivo.; In the ...
In the visual system, prolonged exposure to a high contrast stimulus leads to a decrease in neuronal responsiveness, referred to as contrast adaptation. Contrast adaptation has been extensively studied in carnivores and primates, but has so far received little attention in mice. This thesis explores contrast adaptation and its mechanisms in mouse primary visual cortex (V1). Using extracellular tetrode recordings in mouse V1, I found contrast adaptation to be orientation unspecific. While this finding differs from reports in carnivores and primates, it is consistent with the notion that responsiveness of individual neurons is influenced by the activity history of the local network. Adaptation was also found to be cell-type specific, as putative parvalbumin (PV) expressing interneurons underwent less adaptation than other cell types. There is debate whether adaptation arises within the cortex or is inherited from the earlier stages in the visual pathway (e.g. visual thalamus or retina). In order ...
In this study, we have introduced optimal orientation as a benchmark for evaluating the performance of orientation strategies in given flow conditions. With optimal orientation, trajectories are longest yet travel duration is minimized by steering through regions of relatively high flow support. The illustrated trajectories (figures 1a,b and 2a,b) demonstrate that optimal orientation in horizontal flow does not always involve increased compensation on approach to the goal (cf. [12,13]), can involve either over-drift or over-compensation en route (cf. [23,38]) and is not always equivalent to full drift in balanced flows (contra [12]).. Our results provide insight into the value of information an animal may have about flow conditions. In flow that is weak compared to self-speeds (W ≤ 0.5), flow prediction is not essential as full compensation and goal orientation are all nearly as reliable and efficient as flow-adjusted vector orientation and optimal orientation (figures 1d, 2d and 3d). This ...
This paper describes the performance of a neuronal network model of the input layer 4Cα of macaque V1. This model differs from others in the literature in several ways. (i) It is designed largely from data for the anatomy and physiology of layer 4Cα of macaque (i.e., length scales and patterning of connectivity, and pinwheel centers). (ii) It uses cortical coordinates rather than idealized coordinates as in "ring models" (7, 8, 28) or "near-ring models" (9), whose coordinate labels are angles of orientation preference, rather than cortical locations within the layer. (iii) It has only short-range local inhibition, which is consistent with anatomical data, rather than an inhibition which is explicitly long-range in orientation preference, as is standard for many models (7-9, 31). (iv) It uses membrane potential, driven by synaptic conductances, as the fundamental variables, rather than activities or mean firing rates (7, 8, 32), or a probabilistic "population-density" representation (31, 33, ...
Spike count correlations (SCCs), covariation of neuronal responses across multiple presentations of the same stimulus, are ubiquitous in sensory cortices and span different modalities (1⇓-3) and processing stages (4⇓⇓-7). In the visual system, SCCs, also termed noise correlations, have traditionally been considered to be independent of the stimulus and hence have been thought to impede stimulus encoding (8). Studies on stimulus-independent aspects of SCCs in the primary visual cortex (V1) sought to capture correlation patterns that were solely accounted for by differences in receptive field structure (9, 10). Initial investigations of dependence of SCCs on low-level stimulus features, such as orientation and contrast, focused on the population mean of SCCs (11⇓-13), but stimulus-dependent changes in the mean are modest in awake animals (9, 14). Only recently has orientation and contrast dependence of the fine structure of SCCs been demonstrated in anesthetized cats and awake mice (15). ...
Intracellular recordings from simple cells of the cat visual cortex were used to test linear models for the generation of selectivity for the direction of visual motion. Direction selectivity has been thought to arise in part from nonlinear processes, as suggested by previous experiments that were based on extracellular recordings of action potentials. In intracellular recordings, however, the fluctuations in membrane potential evoked by moving stimuli were accurately predicted by the linear summation of responses to stationary stimuli. Nonlinear mechanisms were not required. ...
The mechanisms of attention prioritize sensory input for efficient perceptual processing. Influential theories suggest that attentional biases are mediated via preparatory activation of task-relevant perceptual representations in visual cortex, but the neural evidence for a preparatory coding model of attention remains incomplete. In this experiment, we tested core assumptions underlying a preparatory coding model for attentional bias. Exploiting multivoxel pattern analysis of functional neuroimaging data obtained during a non-spatial attention task, we examined the locus, time-course, and functional significance of shape-specific preparatory attention in the human brain. Following an attentional cue, yet before the onset of a visual target, we observed selective activation of target-specific neural subpopulations within shape-processing visual cortex (lateral occipital complex). Target-specific modulation of baseline activity was sustained throughout the duration of the attention trial and the degree
r norman ,rsnorman_ at _comcast.net, wrote in message news:,cqqpbvgsktmgosm9sad08spq7l868a7929 at 4ax.com,... , On 9 May 2003 20:05:58 -0700, peer-error at excite.com (External Network , Error) wrote: , , ,Hi: , , , ,I am planning on developing a digital/brain interface. It uses FSK , ,[Frequency Shift Keying] signals. It is in a silicon-chip. This , ,silicon-chip is attached to a subjects visual cortex [chips , ,circuits connected to visual cortexs neurons]. The chip processes , ,FSK. The chip has information about the subjects visual cortex. In , ,order to produce the correct visual perception, it has to: , , , ,1. Convert to FSK information to a language the visual cortex can , ,understand , ,2. Excite the correct region[s] of the visual cortex with the , ,compatible language. , , , ,My design acts by affecting negative neuronal ions in the visual , ,cortex with electrons. The digital electric signal is initially , ,FSK-modulated. This signals format is then altered so that it can , ...
The neural basis of visual perception can be understood only when the sequence of cortical activity underlying successful recognition is known. The early steps in this processing chain, from retina to the primary visual cortex, are highly local, and the perception of more complex shapes requires integration of the local information. In Study I of this thesis, the progression from local to global visual analysis was assessed by recording cortical magnetoencephalographic (MEG) responses to arrays of elements that either did or did not form global contours. The results demonstrated two spatially and temporally distinct stages of processing: The first, emerging 70 ms after stimulus onset around the calcarine sulcus, was sensitive to local features only, whereas the second, starting at 130 ms across the occipital and posterior parietal cortices, reflected the global configuration. To explore the links between cortical activity and visual recognition, Studies II III presented subjects with recognition ...
In the past two decades, sensory neuroscience has moved from describing response properties to external stimuli in cerebral cortex to establishing connections between neuronal activity and sensory perception. The seminal studies by Newsome, Movshon and colleagues in the awake behaving macaque firmly link single cells in extrastriate area V5/MT and perception of motion. A decade later, extrastriate visual cortex appears awash with neuronal correlates for many different perceptual tasks. Examples are attentional signals, choice signals for ambiguous images, correlates for binocular rivalry, stereo and shape perception, and so on. These diverse paradigms are aimed at elucidating the neuronal code for perceptual processes, but it has been little studied how they directly compare or even interact. In this paper, I explore to what degree the measured neuronal signals in V5/MT for choice and attentional paradigms might reflect a common neuronal mechanism for visual perception.
The local orientation structure of a visual image is fundamental to the perception of spatial form. Reports of reliable orientation-selective modulations in the pattern of fMRI activity have demonstrated the potential for investigating the representation of orientation in the human visual cortex. Or …
The striation of a stimulus passing across a complex or supercomplex receptive field of a cats visual cortex (RFVC) defines the characteristics of the fields responses. For each RF (receptive field) an optimum stimulus which evokes a maximum response can be found. The more bands there are in the optimum stimulus, the smaller is the average width of bars and the intervals between them. The effective areas of the stimulus is independent of the number of bands it contains and is equal to 2.6 degrees on the average (in diameter). The column of neurons with identical orientation of the RFs contains fields in which optimum stimuli consist of a different number of bands. These data lead one to assume that the RFVC are narrow-band filters of spatial frequencies and perform a piecewise Fourier transform of the image. A network of such neurons will discern the boundary between textures.*Cerebral cortex
V1 has a very well-defined map of the spatial information in vision. For example, in humans, the upper bank of the calcarine sulcus responds strongly to the lower half of visual field (below the center), and the lower bank of the calcarine to the upper half of visual field. In concept, this retinotopic mapping is a transformation of the visual image from retina to V1. The correspondence between a given location in V1 and in the subjective visual field is very precise: even the blind spots are mapped into V1. In terms of evolution, this correspondence is very basic and found in most animals that possess a V1. In humans and animals with a fovea in the retina, a large portion of V1 is mapped to the small, central portion of visual field, a phenomenon known as cortical magnification.[12] Perhaps for the purpose of accurate spatial encoding, neurons in V1 have the smallest receptive field size of any visual cortex microscopic regions. The tuning properties of V1 neurons (what the neurons respond to) ...
Author Summary How can humans and animals make complex decisions on time scales as short as 100 ms? The information required for such decisions is coded in neural activity and should be read out on a very brief time scale. Traditional approaches to coding of neural information rely on the number of electrical pulses, or spikes, that neurons fire in a certain time window. Although this type of code is likely to be used by the brain for higher cognitive tasks, it may be too slow for fast decisions. Here, we explore an alternative code which is based on the latency of spikes with respect to a reference signal. By analyzing the simultaneous responses of many cells in monkey visual cortex, we show that information about the orientation of visual stimuli can be extracted reliably from spike latencies on very short time scales.
Author: von Pföstl, V et al.; Genre: Poster; Published in Print: 2010-11; Title: Effects of lactate on primary visual cortex of non-human primates investigated by pharmaco mri and neurochemical analysis
TY - JOUR. T1 - Rapid, experience-dependent expression of synaptic NMDA receptors in visual cortex in vivo. AU - Quinlan, Elizabeth M.. AU - Philpot, Benjamin D.. AU - Huganir, Richard L.. AU - Bear, Mark F.. PY - 1999/4/1. Y1 - 1999/4/1. N2 - Sensory experience is crucial in the refinement of synaptic connections in the brain during development. It has been suggested that some forms of experience-dependent synaptic plasticity in vivo are associated with changes in the complement of postsynaptic glutamate receptors, although direct evidence has been lacking. Here we show that visual experience triggers the rapid synaptic insertion of new NMDA receptors in visual cortex. The new receptors have a higher proportion of NR2A subunits and, as a consequence, different functional properties. This effect of experience requires NMDA receptor activation and protein synthesis. Thus, rapid regulation of post- synaptic glutamate receptors is one mechanism for developmental plasticity in the brain. Changes in ...
Even when the primary visual cortical area is absent bilaterally from early life, the rest of a primate visual brain can develop and function normally to support day-to-day visual behaviour.
In this study, we show that top-down control mechanisms engaged during visual imagery of simple shapes (letters X and O) can selectively activate position-invariant perceptual codes in visual areas specialised for shape processing, including lateral occipital complex (LOC). First, we used multivoxel pattern analysis (MVPA) to identify visual cortical areas that code for shape within a position-invariant reference frame. Next, we examined the similarity between these high-level visual codes and patterns elicited while participants imagined the corresponding stimulus at central fixation. Our results demonstrate that imagery engages object-centred codes in higher-level visual areas. More generally, our results also demonstrate that top-down control mechanisms are able to generate highly specific patterns of visual activity in the absence of corresponding sensory input. We argue that a general model of top-down control must account for dynamic modulation of functional connectivity between high-level control
Macular degeneration (MD) causes lesions to the center of the retina. There is no cure for MD but several promising treatments aimed at restoring retinal lesions are under investigation. These restorative treatments, however, rely on the assumption that the patients brain can still process the retinal signals once they are restored. Whether this assumption is correct has yet to be determined. In previous work, we already established that the early visual cortex in MD does not reallocate its resources to processing the intact peripheral visual field (Baseler et al. 2011, Nature Neuroscience 14: 649-655), but it is still possible that long-term visual deprivation leads to visual cortical degeneration (Boucard et al. 2009, Brain 132: 1898-1906). Here, we used functional magnetic resonance imaging (fMRI) and a new fMRI data-analysis tool - connective field modeling (Haak et al. 2012, NeuroImage 66: 376-384) - to evaluate the retinotopic organization of the cortical lesion projection zone (LPZ) in 8 ...
Purpose: : To understand the functional organization of murine visual cortex. Methods: : Single cell impulses are detected by inserting a metal micro-electrode through the dura-covered visual cortex of ketamine/xylazine anesthetized C57/Bl 6 mice, sometimes from two areas simultaneously. The retina of the left or right eye is stimulated with light emitting diodes (370, strong for UV cone opsin; 505 nm, strong for M cone opsin) producing full field stimuli. Eyes are light adapted to suppress rods. Evidence that more than one cone mechanism produces a response is based on selective chromatic adaptation or lack of response univariance; i.e. a response from one cone mechanism to different wavelengths becomes identical at an appropriate energy. Results: : Full field stimuli produce similar responses in all areas of V1, a negative/positive potential with single cell impulses, often of large amplitude. The response is detected at 0.3-0.5 mm below the cortical surface with a latency of about 50 ms. Most ...
Nauhaus, I.*, Nielsen, K.J.*, Disney, A.A., Callaway, E.M. (In press) Orthogonal micro-organization of orientation and spatial frequency in primate primary visual cortex. Nature Neuroscience.. Li Y., Aimone, J.B., Xu, X., Callaway, E.M., Gage, F.H. (2012) Development of GABAergic inputs controls the contribution of maturing neurons to the adult hippocampal network. Proceedings of the National Academy of Sciences 109(11):4290-4295.. Marshel, J.H., Garrett, M.E., Nauhaus, I., Callaway, E.M. (2011) Functional specialization of seven mouse visual cortical areas. Neuron 72(6):1040-1054.. Nauhaus, I., Nielsen, K.J., Callaway, E.M. (2012) Nonlinearity of two-photon Ca2+ imaging yields distorted measurements of tuning for V1 neuronal populations. Journal of Neurophysiology 107(3):923-936.. Nielsen, K.J., Callaway, E.M., Krauzlis, R.J. (2012) Viral vector-based reversible neuronal inactivation and behavioral manipulation in the macaque monkey. Frontiers in Systems Neuroscience 6(48).. Vivar, C., Potter, ...
Our data show that autoregulation in the PCA territory is altered by metabolic activation by eye opening in healthy older adult subjects. As we hypothesized, during eyes open, the PCA vascular bed is vasodilated and BFV is increased to meet the increased neuronal metabolic demand of the visual cortex. In this state, PCA is more vulnerable to blood pressure fluctuations as compared to the MCA territory, as reflected by the higher PCA transfer functions gains in the low-frequency (autoregulatory) range. However, when the eyes are closed and the visual cortex is in a metabolically quiescent state, the PCA autoregulation may be even more effective than the MCA, as shown by the lower gains in the low and cardiac frequency range.. Higher PCA transfer function gains have been previously reported by Haubrich et al5 who studied 30 older adults (mean age, 65±10 years) without cerebrovascular disease or dysautonomia and showed higher gains in the PCA compared to the MCA. However, these subjects were ...
In adults, certain regions of the brains visual cortex respond preferentially to specific types of input, such as faces or objects-but how and when those preferences arise has long puzzled neuroscientists.
If you have a question about this talk, please contact John Mollon.. The surface area of human primary visual cortex (V1) varies substantially between individuals for reasons that are unknown. However, such variability is typically ignored by the vast majority of studies focusing only on commonalities in perception and visual processing. In this talk, I will discuss our recent lines of investigations in which we instead used functional MRI and magnetoencephalography (MEG) to study the link between visual cortical architecture, neural response properties in the visual system and subjective perception.. This talk is part of the Craik Club series.. ...
We have shown that visual stimulation results in strong and rapid hemodynamic responses in primary visual cortex of awake mice and that both the amplitude and time course of neurovascular coupling depend critically on anesthesia and wakefulness. We ascribe these effects to neurovascular coupling because they were not accompanied by differences in spike responses (at least at the level of population rates) and they were replicated (at least in time course) by direct optogenetic stimulation of the cortex.. These results indicate that hemodynamic activity in mice is best measured during wakefulness. Indeed, in awake mice, we routinely obtained clear maps of retinotopy of quality comparable if not superior to those obtained under anesthesia. Hemodynamic responses were larger and faster than under anesthesia and were similar whether the mice were sitting or running. If ones experiment instead requires anesthesia, then it seems better to use urethane than isoflurane: under isoflurane, responses were ...
The molecular basis for the decline in experience-dependent neural plasticity over age remains poorly understood. In visual cortex, the robust plasticity induced in juvenile mice by brief monocular deprivation during the critical period is abrogated by genetic deletion of Arc, an activity-dependent regulator of excitatory synaptic modification. Here, we report that augmenting Arc expression in adult mice prolongs juvenile-like plasticity in visual cortex, as assessed by recordings of ocular dominance (OD) plasticity in vivo. A distinguishing characteristic of juvenile OD plasticity is the weakening of deprived-eye responses, believed to be accounted for by the mechanisms of homosynaptic long-term depression (LTD). Accordingly, we also found increased LTD in visual cortex of adult mice with augmented Arc expression and impaired LTD in visual cortex of juvenile mice that lack Arc or have been treated in vivo with a protein synthesis inhibitor. Further, we found that although activity-dependent ...
Perception is shaped by both bottom-up inputs and top-down expectations. Here, we observed a direct neural correlate of this integration of inputs and priors in early visual cortex. Previous studies have shown that sensory representations in early visual cortex can be classified (Haynes and Rees, 2005; Kamitani and Tong, 2005, 2006) and reconstructed (Miyawaki et al., 2008; Brouwer and Heeger, 2009, 2011; Naselaris et al., 2009) on the basis of mesoscale fMRI signals during passive viewing of visual stimuli, and that these representations are also present in absence of sensory stimulation, for example during working memory maintenance (Harrison and Tong, 2009; Riggall and Postle, 2012). Additionally, representations in visual cortex have been shown to reflect arbitrary perceptual decisions about randomly moving dot patterns (Serences and Boynton, 2007b). While these previous studies investigated either bottom-up-induced or top-down-induced sensory representations in isolation, here we show that ...
There is a substantial number of studies investigating how the primate brain performs visual search tasks, often focusing on cortical structures (e.g., Bichot, Rossi, & Desimone, 2005, Chelazzi, Miller, Duncan, & Desimone, 1993). While it was speculated for some time that only animals with large a neocortex may have mechanisms of visual search, it now seems clear that a structure like a neocortex is not necessary for pop-out sensitivity. But what then are the minimal requirements? Clearly, the responses within the classical receptive field of neurons are not enough; there must also be interactions between cells beyond the classical receptive field. In fact, the saliency model of Li (2002) proposes that horizontal connections between neurons in V1 provide enough contextual information to mediate the saliency of a stimulus. In birds, such substrates may be found in the the avian visual Wulst, which resembles in many respects the mammalian visual cortex (Nieder & Wagner, 1999; Pettigrew & Konishi, ...
A myriad of mechanisms have been suggested to account for the full richness of visual cortical plasticity. We found that visual cortex lacking Arc is impervious to the effects of deprivation or experience. Using intrinsic signal imaging and chronic visually evoked potential recordings, we found that …
Visual area MT is a model of choice in primate neurophysiological and human imaging research of visual perception, due to its considerable sensitivity to moving stimuli and the strong direction selectivity of its neurons. While the location of MT(V5) in the non-human primate is easily identifiable based on gross anatomy and appears consistent between animals, this is less the case in human subjects. Functional localisation of human MT+ with moving stimuli can identify a group of motion-sensitive regions, but defining MT proper has proved more challenging. In this review we consider approaches to studying the cyto- and myleoarchitecture of this cortical area that may, in the future, allow identification of human MT in vivo based on anatomy.
Humans survive in environments that contain a vast quantity and variety of visual information. All items of perceived visual information must be represented within a limited number of brain networks. The human brain requires mechanisms for selecting only a relevant fraction of perceived information for more in-depth processing, where neural representations of that information may be actively maintained and utilized for goal-directed behavior. Object-based attention is crucial for goal-directed behavior and yet remains poorly understood. Thus, in the study we investigate how neural representations of visual object information are guided by selective attention. The magnitude of activation in human extrastriate cortex has been shown to be modulated by attention; however, object-based attention is not likely to be fully explained by a localized gain mechanism. Thus, we measured information coded in spatially distributed patterns of brain activity with fMRI while human participants performed a task ...
Microsoft Visual C# 2008 (MS Visual C# 2008) allows Visual C# 2008 programmers to rapidly create Windows applications for their end users. (C# is pronounced c-sharp). Visual C# 2008 developers can extend the standard functionality available inside the Visual C# 2008 IDE with a variety of Visual C# 2008 add-ins and Visual C# 2008 tools. The extensibility of Visual C# 2008 is one of the main reasons it has proved to be popular with developers, as Visual C# 2008 software engineers can find Visual C# 2008 downloads from other companies or other VC# developers to act as a Visual C# 2008 extension to their Visual C# 2008 IDE or Visual C# 2008 app.. The versatility of Visual C# 2008 also extends to various forms of Visual C# 2008 software components. Visual C# 2008 controls can be used to create feature rich Visual C# 2008 user interfaces on forms and Web pages inside Visual C# 2008 apps. These Visual C# 2008 UI controls are augmented by non-visual Visual C# 2008 components or Visual C# 2008 libraries ...
When you are awake and see something, the stimuli comes in through your retina, through your primary visual cortex, then over to your secondary and tertiary visual cortices, etc. But during REM sleep, the activity starts in the secondary and tertiary cortices rather than the primary visual cortex. In other words, those parts of your brain are processing things even though you arent actually seeing anything - you are dreaming. ...
This book provides the essential facts about how visual information is processed in the brain. The book has 16 chapters. Chapter 1 provides basic information about the methods that are used by ... More. This book provides the essential facts about how visual information is processed in the brain. The book has 16 chapters. Chapter 1 provides basic information about the methods that are used by investigators to find out how visual information is processed in living organisms. Chapter 2 outlines the brain areas that process visual information and specifies how these areas are interconnected in the mammalian visual system. Chapter 3 describes in detail the structural and functional organization of the retina. Chapter 4 describes the lateral geniculate nucleus. Chapter 5 delineates the manner in which the primary visual cortex, area V1, is organized. Chapter 6 examines the organization and function of higher cortical visual areas. In Chapter 7 the ON and OFF channels that originate in the retina are ...
A day by day log of cortical electric activity in the mouse visual cortex was published in the Journal of Neuroscience by George Washington University (GW) researcher Matthew Colonnese, Ph.D. This research is the first to ...
Which part of the brain is responsible?. The visual cortex, at the back of your brain.. Why does this happen?. Being able to process information from your eyes is important; it allows you to form a picture of the world around you. This processing happens in the visual cortex, which is right at the back of your brain. Visual information enters through your eyes where the retina converts light into electrical signals. These are transmitted along the optic nerves to the visual cortex where they are decoded and a "picture" of what you are seeing is built and presented to your consciousness. In order to do this job correctly the visual cortex requires a lot of brain space. In fact, more than a third of the human brain is devoted to decoding what we look at, making it the largest single brain system. And different aspects, or types of visual information are analysed and processed by different parts of the brain. One brain area decodes colours, another processes faces, yet more decode shapes, and ...
I wanted the title of this post to be "A tale of two one two three papers" but I couldnt figure out how to get strikethroughs in the title field. And I thought "A tale of two, make that one, no make that two again, oops now three" might be a bit cumbersome. As promised, heres another installment of the discussion of what happens when we receive conceptually related/overlapping papers. It starts with a paper that appeared just yesterday in Neuron by Kenichi Ohki and colleagues describing how mouse visual cortex neurons that developed from the same neural progenitor cell tend to be more similar functionally than those that did not.. Why is this significant? First a little background. Cells in visual cortex are tuned to different aspects of visual stimuli, such as orientation or direction, and anatomically are organized quite specifically. Cells with similar preferences tend to cluster together and to be selectively connected with each other (though to differing degrees in different species), and ...
During the early postnatal development of the neocortex in rats there is an axonal projection from the occipital cortex (which includes the visual cortex) to the spinal cord which is subsequently completely removed through a process of selective coll
Abstract Stimulus-reward coupling without attention can induce highly specific perceptual learning effects, suggesting that reward triggers selective plasticity within visual cortex. Additionally, dopamine-releasing events-temporally surrounding stimulus-reward associations-selectively enhance memory. These forms of plasticity may be evoked by selective modulation of stimulus representations during dopamine-inducing events. However, it remains to be shown whether dopaminergic signals can selectively modulate visual cortical activity. We measured fMRI activity in monkey visual cortex during reward-only trials apart from intermixed cue-reward trials. Reward without visual stimulation selectively decreased fMRI activity within the cue representations that had been paired with reward during other trials. Behavioral tests indicated that these same uncued reward trials strengthened cue-reward associations. Furthermore, such spatially-specific activity modulations depended on prediction error, as shown ...
Involvement of bidirectional modification at excitatory synapses in experience-dependent cortical maturation has been supported by various experimental data in visual cortex. Experiments using slice p
Today, researchers routinely record neuronal activity in rodents for months at a time (techniques such as calcium imaging allow one to examine the activity of the same neurons from one day to the next), but the surgical procedure of attaching head implants is quite drastic. In most cases, the animals are scalped (nonviolently, of course), holes are drilled in the skull, and after the electrodes are inserted into the brain, the scalp is replaced with glue (usually dental cement). Researchers take great care to perform such procedures in a sterile environment to reduce the risk of infections. Inevitably, however, after months (or in lucky cases, perhaps a year), the implants fall off.. Girmans original solution to this problem was to not scalp the animals in the first place. Instead, he would only make holes large enough for the electrodes to pass through (0.12 mm, according to his paper). Then, he would create a platform for the electronic equipment by threading stiff metal wires under the ...
Author Summary Simple cells in the primary visual cortex (V1) demonstrate many response properties that are either nonlinear or involve response modulations (i.e., stimuli that do not cause a response in isolation alter the cells response to other stimuli). These non-classical receptive field (nCRF) effects are generally modeled individually and their collective role in biological vision is not well understood. Previous work has shown that classical receptive field (CRF) properties of V1 cells (i.e., the spatial structure of the visual field responsive to stimuli) could be explained by the sparse coding hypothesis, which is an optimal coding model that conjectures a neural population should use the fewest number of cells simultaneously to represent each stimulus. In this paper, we have performed extensive simulated physiology experiments to show that many nCRF response properties are simply emergent effects of a dynamical system implementing this same sparse coding model. These results suggest that
Simple features, such as particular edges of the image in a specific orientation, are extracted at the first cortical processing stage, called the primary visual cortex, or V1. Then subsequent cortical processing stages, V2, V4, etc., extract progressively more complex features, culminating in the inferotemporal cortex where that essential "viewpoint invariant object identification" is thought to occur. But, most of the connections in the human brain do not project up the cortical hierarchy, as might be expected from gross neuroanatomy, but rather connect neurons located at the same hierarchical level, called lateral connections, and also project down the cortical hierarchy to lower processing levels ...
The switching of one image for another may involve selecting one of the images as the percept or selecting one of the eyes. Blake et al. (1979) performed an experiment in which subjects could change the image at a given eye by pressing a button. When a particular image became dominant they pressed a button to change the image at the eye receiving the dominant image for the non-dominant image. They found that the subjects immediately experienced the second image as the dominant image. This suggests that binocular rivalry is selecting between eyes rather than images. Lehky in 1988 proposed that the switching may be occurring as a result of feedback between visual cortical area V1 and the Lateral Geniculate Nucleus (a thalamic relay - see Carandini et al. 2002) and Blake in 1989 also proposed that the switching occurred at the level of area V1. (Visual cortical area V1 receives visual input direct from the LGN.) Tong (2001) has argued that, in humans, the switching of images in binocular rivalry ...
The switching of one image for another may involve selecting one of the images as the percept or selecting one of the eyes. Blake et al. (1979) performed an experiment in which subjects could change the image at a given eye by pressing a button. When a particular image became dominant they pressed a button to change the image at the eye receiving the dominant image for the non-dominant image. They found that the subjects immediately experienced the second image as the dominant image. This suggests that binocular rivalry is selecting between eyes rather than images. Lehky in 1988 proposed that the switching may be occurring as a result of feedback between visual cortical area V1 and the Lateral Geniculate Nucleus (a thalamic relay - see Carandini et al. 2002) and Blake in 1989 also proposed that the switching occurred at the level of area V1. (Visual cortical area V1 receives visual input direct from the LGN.). Tong (2001) has argued that, in humans, the switching of images in binocular rivalry ...
Here we use a perturbative approach to compute the ground states of the EN for the joint mapping of two visual features: (i) position in visual space, represented in a retinotopic map and (ii) line orientation, represented in an orientation preference map (OPM). In this framework, the EN incooporates a mapping from a four-dimensional feature space to the twodimensional cortical sheet of neurons. We show that the dynamics of both feature representations can be treated within a general theory for the stability of OPMs [6]. We find various ground states as a function of the lateral intracortical interactions and external stimulus distribution properties. However, in all parameter regimes, the grounds states of the Elastic Network Model are either stripe-like, or crystalline representation of the two visual features. We present a complete phase diagram of the model, summarizing pattern selection. Analytical predictions are confirmed by direct numerical simulations. Our results question previous ...