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
TY - JOUR. T1 - Dynamics of orientation tuning in macaque primary visual cortex. AU - Ringach, Dario L.. AU - Hawken, Michael J.. AU - Shapley, Robert. PY - 1997/5/15. Y1 - 1997/5/15. N2 - Orientation tuning of neurons is one of the chief emergent characteristics of the primary visual cortex, VI. Neurons of the lateral geniculate nucleus, which comprise the thalamic input to V1, are not orientation-tuned, but the majority of V1 neurons are quite selective. How orientation tuning arises within VI is still controversial. To study this problem, we measured how the orientation tuning of neurons evolves with time 20 using a new method: reverse correlation in the orientation domain. Orientation tuning develops after a delay of 30-45 milliseconds and persists for 40-85 ms. Neurons in layers 4Cα or 4Cβ, which receive direct input from the thalamus, show a single orientation preference which remains unchanged throughout the response period. In contrast, the preferred orientations of output layer ...
In two experiments, magnetoencephalography (MEG) was used to investigate the effects of motion on gamma oscillations in human early visual cortex. When presented centrally, but not peripherally, stationary and moving gratings elicited several evoked and induced response components in early visual cortex. Time-frequency analysis revealed two nonphase locked gamma power increases-an initial, rapidly adapting response and one sustained throughout stimulus presentation and varying in frequency across observers from 28 to 64 Hz. Stimulus motion raised the sustained gamma oscillation frequency by a mean of approximately 10 Hz. The largest motion-induced frequency increases were in those observers with the lowest gamma response frequencies for stationary stimuli, suggesting a possible saturation mechanism. Moderate gamma amplitude increases to moving versus stationary stimuli were also observed but were not correlated with the magnitude of the frequency increase. At the same site in visual cortex, sustained
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 ...
One of the most prominent characteristics of the human neocortex is its laminated structure. The first person to observe this was Francesco Gennari in the second half the 18th century: in the middle of the depth of primary visual cortex, myelinated fibres are so abundant that he could observe them
TY - JOUR. T1 - Large-scale remapping of visual cortex is absent in adult humans with macular degeneration. AU - Baseler, Heidi A.. AU - Gouws, Andre. AU - Haak, Koen V.. AU - Racey, Christopher. AU - Crossland, Michael D.. AU - Tufail, Adnan. AU - Rubin, Gary S.. AU - Cornelissen, Frans W.. AU - Morland, Antony B.. PY - 2011/5. Y1 - 2011/5. N2 - The occipital lobe contains retinotopic representations of the visual field. The representation of the central retina in early visual areas (V1-3) is found at the occipital pole. When the central retina is lesioned in both eyes by macular degeneration, this region of visual cortex at the occipital pole is accordingly deprived of input. However, even when such lesions occur in adulthood, some visually driven activity in and around the occipital pole can be observed. It has been suggested that this activity is a result of remapping of this area so that it now responds to inputs from intact, peripheral retina. We evaluated whether or not remapping of ...
|jats:p| 1. Twenty-four patients with electrodes chronically implanted on the surface of extrastriate visual cortex viewed faces, equiluminant scrambled faces, cars, scrambled cars, and butterflies. 2. A surface-negative potential, N200, was evoked by faces but not by the other categories of stimuli. N200 was recorded only from small regions of the left and right fusiform and inferior temporal gyri. Electrical stimulation of the same region frequently produced a temporary inability to name familiar faces. 3. The results suggest that discrete regions of inferior extrastriate visual cortex, varying in location between individuals, are specialized for the recognition of faces. These face modules appear to be intercalated among other functionally specific small regions. |/jats:p|
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
Orientation and ocular dominance maps in the primary visual cortex of mammals are among the most thoroughly investigated of the patterns in the cerebral cortex. A considerable amount of work has been dedicated to unraveling both their detailed structure and the neural mechanisms that underlie their formation and development. Many schemes have been proposed, some of which are in competition. Some models focus on development of receptive fields while others focus on the structure of cortical maps, i.e., the arrangement of receptive field properties across the cortex. Each model used different means to determine its success at reproducing experimental map patterns, often relying principally on visual comparison. Experimental data are becoming available that allow a more careful evaluation of models. In this contribution more than 10 of the most prominent models of cortical map formation and structure are critically evaluated and compared with the most recent experimental findings from macaque ...
Our results provide the first evidence that temporal expectation modulates the power and coherence of gamma responses already at the earliest stage of cortical visual processing. It has been shown that the power and synchronization of gamma oscillations can be modulated by spatial and feature selective attention (Müller et al., 2000; Fries et al., 2001, 2008; Bichot et al., 2005; Taylor et al., 2005; Buschman and Miller, 2007). Our findings extend this notion to the temporal domain.. Fries et al. (2001, 2008) found that gamma synchronization in area V4 was stronger when attention was directed to a stimulus inside the RF. The expectation effects we found in V1 are of comparable magnitude as those found for spatial attention in V4. However, the effects of expectation in V1 are not confined to the attended location (here the fixation point), since the modulation in gamma was comparable for sites recorded simultaneously in the central and peripheral representations of the visual field. These ...
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.
Positron-emission tomography (PET) can localize functions of the human brain by imaging regional cerebral blood flow (CBF) during voluntary behaviour. Functional brain mapping with PET, however, has been hindered by PETs poor spatial resolution (typically ,1 cm). We have developed an image-analysis strategy that can map functional zones not resolved by conventional PET images. Brain areas selectively activated by a behavioural task can be isolated by subtracting a paired control-state image from the task-state image, thereby removing areas not recruited by the task. When imaged in isolation the centre of an activated area can be located very precisely. This allows subtle shifts in response locale due to changes in task to be detected readily despite poor spatial resolution. As an initial application of this strategy we mapped the retinal projection topography of human primary visual cortex. Functional zones separated by less than 3 mm (centre-to-centre) were differentiated using PET CBF images ...
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
The first stage of visual processing in the cortex is called V1. In primates, V1 creates a saliency map (highlights what is important) from visual inputs to guide the shifts of attention known as gaze shifts.[13] It does so by transforming visual inputs to neural firing rates from millions of neurons, such that the visual location signalled by the highest firing neuron is the most salient location to attract gaze shift. V1s firing rates are received by the superior colliculus (in the mid-brain) which reads out the V1 activities to guide gaze shifts. V1 has a very well-defined map of the spatial information in vision. For example, in humans, the upper bank of the calcarine sulcus (in the occipital lobe) 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 ...
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.
While recent studies of synaptic stability in adult cerebral cortex have focused on dendrites, how much axons change is unknown. We have used advances in axon labeling by viruses and in vivo two-photon microscopy to investigate axon branching and bouton dynamics in primary visual cortex (V1) of adul …
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 ...
We generated probabilistic area maps and maximum probability maps (MPMs) for a set of 18 retinotopic areas previously mapped in individual subjects (Georgieva et al., 2009 and Kolster et al., 2010) using four different inter-subject registration methods. The best results were obtained using a recently developed multimodal surface matching method. The best set of MPMs had relatively smooth borders between visual areas and group average area sizes that matched the typical size in individual subjects. Comparisons between retinotopic areas and maps of estimated cortical myelin content revealed the following correspondences: (i) areas V1, V2, and V3 are heavily myelinated; (ii) the MT cluster is heavily myelinated, with a peak near the MT/pMSTv border; (iii) a dorsal myelin density peak corresponds to area V3D; (iv) the phPIT cluster is lightly myelinated; and (v) myelin density differs across the four areas of the V3A complex. Comparison of the retinotopic MPM with cytoarchitectonic areas, including those
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 ...
Comparison of the effects of dark rearing and binocular suture on development and plasticity of cat visual cortex. Brain Res. 1981 Sep 14; 220(2):255-67 ...
In the experiments, we presented a set of picture stimuli to a neuron and recorded a set of noisy responses. We used a regularized pseudoinverse method (see Materials and Methods) to estimate the receptive-field map that describes the linear portion of each response of the cells. This incorporates a simple a priori constraint: the sensitivity of the receptive-field estimate should change smoothly as a function of two-dimensional location within the receptive field (Eq. 8). This constraint reduces the noise in the receptive-field estimates, increasing the spatial resolution possible from the limited number of stimulus presentations.. Figure 4 compares receptive-field reconstructions and their two-dimensional Fourier spectra performed with reversed correlation and the regularized pseudoinverse methods. Fields are shown for three cells and five different values of the regularization parameter λ. This parameter balances the constraints of response prediction and smooth receptive fields. For most ...
Visual neurons respond selectively to specific features that become increasingly complex in their form and dynamics from the eyes to the cortex. Retinal neurons prefer localized flashing spots of light, primary visual cortical (V1) neurons moving bars, and those in higher cortical areas, such as middle temporal (MT) cortex, favor complex features like moving textures. Whether there are general computational principles behind this diversity of response properties remains unclear. To date, no single normative model has been able to account for the hierarchy of tuning to dynamic inputs along the visual pathway. Here we show that hierarchical application of temporal prediction - representing features that efficiently predict future sensory input from past sensory input - can explain how neuronal tuning properties, particularly those relating to motion, change from retina to higher visual cortex. This suggests that the brain may not have evolved to efficiently represent all incoming information, as implied
© 2019 The Author(s) 2019. Published by Oxford University Press. All rights reserved. The primate visual system contains myriad feedback projections from higher-to lower-order cortical areas, an architecture that has been implicated in the top-down modulation of early visual areas during working memory and attention. Here we tested the hypothesis that these feedback projections also modulate early visual cortical activity during the planning of visually guided actions. We show, across three separate human functional magnetic resonance imaging (fMRI) studies involving object-directed movements, that information related to the motor effector to be used (i.e., limb, eye) and action goal to be performed (i.e., grasp, reach) can be selectively decoded-prior to movement-from the retinotopic representation of the target object(s) in early visual cortex. We also find that during the planning of sequential actions involving objects in two different spatial locations, that motor-related information can be
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.. ...
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 ...
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, ...
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 ...
TY - JOUR. T1 - Morphological variation of layer III pyramidal neurones in the occipitotemporal pathway of the macaque monkey visual cortex. AU - Elston, Guy N.. AU - Rosa, Marcello G.P.. PY - 1998/5/28. Y1 - 1998/5/28. N2 - We compared the morphological characteristics of layer III pyramidal neurones in different visual areas of the occipitotemporal cortical stream, which processes information related to object recognition in the visual field (including shape, colour and texture). Pyramidal cells were intracellularly injected with Lucifer Yellow in cortical slices cut tangential to the cortical layers, allowing quantitative comparisons of dendritic field morphology, spine density and cell body size between the blobs and interblobs of the primary visual area (V1), the interstripe compartments of the second visual area (V2), the fourth visual area (V4) and cytoarchitectonic area TEO. We found that the tangential dimension of basal dendritic fields of layer III pyramidal neurones increases from ...
Dopaminergic pathway and primary visual cortex are involved in the freezing of gait in Parkinsons disease: a PET-CT study Yongtao Zhou,1 Junwu Zhao,1,2 Yaqin Hou,3 Yusheng Su,3 Piu Chan,1 Yuping Wang11The Department of Neurology, Xuanwu Hospital of Capital Medical University, Beijing, Peoples Republic of China; 2The Nuclear Medicine Department, Xuanwu Hospital of Capital Medical University, Beijing, Peoples Republic of China; 3The Department of Neurology, Weihai Municipal Hospital, Shandong, Peoples Republic of ChinaBackground: Freezing of gait (FOG) could be partly alleviated by dopaminergic drugs but the mechanism still needs to be elucidated. The purpose of this study is to explore the mechanisms of FOG by vesicular monoamine transporter VMAT2 distribution with the 18,F-AV133 tracer and 18-fludeoxyglucose positron emission tomography-computed tomography (18,F-FDG PET-CT).Methods: Clinical material and PET-CT data were collected from 20 patients with FOG and 147 patients without FOG from November
Cortical circuits are sensitive to experience during well-defined intervals of early postnatal development called critical periods (1). After the critical period, plasticity is reduced or absent. Monocular deprivation (MD) is a classic model of experience-dependent plasticity. MD during the critical period results in a shift of ocular dominance (OD) of cortical neurons in favor of the nondeprived eye (2, 3). No OD shift is seen after MD in adult animals. The factors responsible for the cessation of OD plasticity in adults are only partially known. There is some evidence that the developmental increase in intracortical inhibition reduces plasticity and contributes to the termination of the critical period (4-6). However, other factors present in the adult visual cortex could stabilize synaptic connections and limit experience-dependent plasticity. CSPGs are attractive candidates for this role. CSPGs are components of the ECM that inhibit axonal sprouting and growth (7-9). Their adult pattern of ...
CiteSeerX - Document Details (Isaac Councill, Lee Giles, Pradeep Teregowda): this article we investigate to what extent the statistical properties of natural images can be used to understand the variation of receptive field properties of simple cells in the mammalian primary visual cortex. The receptive fields of simple cells have been studied extensively (e.g., Hubel & Wiesel 1968, DeValois et al. 1982a, DeAngelis et al. 1993): they are localised in space and time, have band-pass characteristics in the spatial and temporal frequency domains, are oriented, and are often sensitive to the direction of motion of a stimulus. Here we will concentrate on the spatial properties of simple cells. Several hypotheses as to the function of these cells have been proposed. As the cells preferentially respond to oriented edges or lines, they can be viewed as edge or line detectors. Their joint localisation in both the spatial domain and the spatial frequency domain has led to the suggestion that they mimic Gabor
Synaptic plasticity plays a key role in processes of learning and memory. Long-term potentiation (LTP) is a relatively stable enhancement of synaptic transmission following specific patterns of electrical stimulation. Some types of learning (e.g. motor learning, fear conditioning) result in LTP-like changes at synapses. However, no studies have examined LTP-like plasticity in the visual cortex as a result of visual discrimination learning. A visual discrimination task was used to examine changes in LTP in the primary visual cortex (V1) of adult rats. Rats were placed in a Y-shaped water maze and required to swim to one choice arm containing a hidden platform. Distinct visual cues indicated the presence (CS+) and absence (CS-) of the platform. Rats learned to reliably discriminate the visual cues to successfully navigate the maze. Control rats received the same procedure, but the visual cues did not have a predictive relation with the platform. Following training, trained, control, and ...
GENESIS Turtle Cortex Model README file ======================================= This is the large scale model of turtle visual cortex (the NGU model) described in: Nenadic, Z., Ghosh, B.K. and Ulinski. P. (2003) Propagating Waves in Visual Cortex: A Large Scale Model of Turtle Visual Cortex, J. Computational Neuroscience 14:161-184. and Nenadic, Z., Ghosh, B.K. and Ulinski. P. (2002) Modeling and Estimation Problems in the Turtle Visual Cortex, IEEE Trans. Bio-Med. Eng., 49:753-762 It is also described in considerable detail in the file TurtleVisCortex-descrip.pdf, which is included in this archive. This README file tells how to run the simulation with GENESIS. To run the simulation --------------------- 1. If you do not have the GENESIS simulator installed, download it from the GENESIS web site at http://genesis-sim.org/GENESIS. It is available in source and binary versions for UNIX/Linux, MAC OSX, and Windows with Cygwin. Follow the installation instructions provided with the GENESIS ...
We report the application of Optical coherence tomography (OCT) for visualizing a one dimensional depth resolved functional structure of cat brain in vivo. The OCT system is based on the known fact that neural activation induces structural changes such as capillary dilation and cellular swelling. Detecting these changes as an amplitude change of the scattered light, an OCT signal reflecting neural activity i.e., fOCT (functional OCT) could be obtained. Experiments have been done to obtain a depth resolved stimulus-specific profile of activation in cat visual cortex. Our results in one dimension indicate that indeed an orientation dependent functional signal could be obtained. Further, we show that this depth resolved fOCT signal is well correlated with the stimulus dependent column determined by OISI. Based on the results, the smallest functional unit in depth, resolved by the proposed system is around 40 micrometers . We are extending our system to perform two dimensional functional imaging ...
TY - JOUR. T1 - Population receptive field shapes in early visual cortex are nearly circular. AU - Lerma-Usabiaga, Garikoitz. AU - Winawer, Jonathan. AU - Wandell, Brian A.. N1 - Funding Information: Received Dec. 3, 2020; revised Jan. 3, 2021; accepted Jan. 10, 2021. Author contributions: G.L.-U., J.W., and B.A.W. designed research; G.L.-U., J.W., and B.A.W. performed research; G.L.-U. analyzed data; G.L.-U., J.W., and B.A.W. wrote the paper. This work was supported by the European Unions Horizon 2020 Research and Innovation Program under the Marie Sklodowska-Curie Grant 795807 (to G.L.-U.) and by National Institutes of Health Grants EY027401, EY027964, and MH111417 (to J.W.). We thank E. Silson, C. Baker, and R. Reynolds. We also thank R. Reynolds for help with the AFNI software. The authors declare no competing financial interests. Correspondence should be addressed to Garikoitz Lerma-Usabiaga at [email protected] https://doi.org/10.1523/JNEUROSCI.3052-20.2021 Copyright © 2021 the ...
Behavioral studies have reported reduced spatial attention in amblyopia, a developmental disorder of spatial vision. However, the neural populations in the visual cortex linked with these behavioral spatial attention deficits have not been identified. Here, we use functional MRI-informed electroencephalography source imaging to measure the effect of attention on neural population activity in the visual cortex of human adult strabismic amblyopes who were stereoblind. We show that compared with controls, the modulatory effects of selective visual attention on the input from the amblyopic eye are substantially reduced in the primary visual cortex (V1) as well as in extrastriate visual areas hV4 and hMT+. Degraded attentional modulation is also found in the normal-acuity fellow eye in areas hV4 and hMT+ but not in V1. These results provide electrophysiological evidence that abnormal binocular input during a developmental critical period may impact cortical connections between the visual cortex and ...
For years, neural activity in the brains visual cortex was thought to have only one job: to create visual perceptions. A new study by researchers at MITs Picower Institute for Learning and Memory shows that visual cortical activity can serve another purpose -- connecting visual experience with non-visual events.. The study, slated to appear in the March 17 issue of Science, implies that sensory parts of the brain may be able to accomplish more complex tasks than previously imagined, according to co-authors Marshall G. Shuler, MIT research affiliate, and Mark F. Bear, professor of brain and cognitive sciences. The findings have implications for understanding how our brains imbue sensory experience with behavioral meaning.. Electrodes were implanted in the visual cortex of adult rats. Initially, as expected, their neurons responded only to light. However, as the animal repeatedly experienced a light stimulus with the delivery of a drop of water, the neuronal activity changed. And in many cases, ...
The sensory recruitment model envisages visual working memory (VWM) as an emergent property that is encoded and maintained in sensory (visual) regions. The model implies that enhanced sensory-perceptual functions, as in synaesthesia, entail a dedicated VWM-system, showing reduced visual cortex activity as a result of neural specificity. By contrast, sensory-perceptual decline, as in old age, is expected to show enhanced visual cortex activity as a result of neural broadening. To test this model, young grapheme-color synaesthetes, older adults and young controls engaged in a delayed pair-associative retrieval and a delayed matching-to-sample task, consisting of achromatic fractal stimuli that do not induce synaesthesia. While a previous analysis of this dataset (Pfeifer et al., 2016) has focused on cued retrieval and recognition of pair-associates (i.e., long-term memory), the current study focuses on visual working memory and considers, for the first time, the crucial delay period in which no visual
The characterisation of the extravascular (EV) contribution to the blood oxygenation level-dependent (BOLD) effect is important for understanding the spatial specificity of BOLD contrast and for modelling approaches that aim to extract quantitative metabolic parameters from the BOLD signal. Using bipolar crusher gradients, total (b = 0 s/mm(2) ) and predominantly EV (b = 100 s/mm(2) ) gradient echo BOLD ΔR(2)* and signal changes (ΔS/S) in response to visual stimulation (flashing checkerboard; f = 8 Hz) were investigated sequentially (within | 3 h) at 1.5, 3.0 and 7.0 T in the same subgroup of healthy volunteers (n = 7) and at identical spatial resolutions (3.5 × 3.5 × 3.5 mm(3)). Total ΔR(2)* (z-score analysis) values were -0.61 ± 0.10 s(-1) (1.5 T), -0.74 ± 0.05 s(-1) (3.0 T) and -1.37 ± 0.12 s(-1) (7.0 T), whereas EV ΔR(2)* values were -0.28 ± 0.07 s(-1) (1.5 T), -0.52 ± 0.07 s(-1) (3.0 T) and -1.25 ± 0.11 s(-1) (7.0 T). Although EV ΔR(2)* increased linearly with field, as expected, it
The distribution of orientation-selective cells in the primary visual cortex has been found to reflect the first-order statistics of visual inputs, i.e. which orientations are most common during a critical period [1]. Similarly, some properties of the lateral connections between these cells have been found to reflect the second-order statistics of images, i.e. the coocurrence statistics of oriented edge elements, but the results have differed by species. Specifically, horizontal connections have been found to be elongated along the axis of preferred orientation in tree shrew [2] and owl monkey [3], but not in macaque [4]. It is unclear whether these results indicate genuine species differences, or perhaps differences in the visual environments in which these animals were raised. Here we analyse the effect of input statistics on lateral excitatory connectivity in a developmental model of primary visual cortex, by relating differences in co-occurence statistics of distinct image datasets, analysed ...
In the fetal and neonatal monkey, periodically organized regions of high activity of acetylcholinesterase were found in the visual cortical area V2 (Area 18). The acetylcholinesterase bands, like the thin and thick stripes of cytochrome oxidase, were found to run orthogonal to the area 17/18 border. During neonatal development these bands progressively narrow and finally disappear shortly after four months of age.
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Neocortical interneurons display great morphological and physiological variability and are ideally positioned to control circuit dynamics, although their exact role is still poorly understood. To better understand this diversity, we have performed a detailed anatomical and physiological characterization of 3 subtypes of visual cortex interneurons, isolated from transgenic mice which express green fluorescent protein in somatostatin, parvalburnin, and neuropeptide Y positive neurons. We find that these 3 groups of interneurons have systematic differences in dendritic and axonal morphologies and also characteristically differ in the frequencies, amplitude, and kinetics of the spontaneous excitatory and inhibitory synaptic currents they receive. Moreover, we detect a correlation between the kinetics of their synaptic inputs and quantitative aspects of their axonal arborizations. This suggests that different interneuron types could channel different temporal patterns of activity. Our results also ...
Research Interest Visual neurophysiology and perception. Publications Lopour Beth A, Tavassoli Abtine, Fried Itzhak, Ringach Dario L Coding of information in the phase of local field potentials within human medial temporal lobe Neuron, 2013; 79(3): 594-606.. Paik Se-Bum, Ringach Dario L Link between orientation and retinotopic maps in primary visual cortex Proceedings of the National Academy of Sciences of the United States of America, 2012; 109(18): 7091-6.. Nauhaus Ian, Busse Laura, Ringach Dario L, Carandini Matteo Robustness of traveling waves in ongoing activity of visual cortex The Journal of neuroscience : the official journal of the Society for Neuroscience, 2012; 32(9): 3088-94.. Frey Jared, Ringach Dario L Binocular eye movements evoked by self-induced motion parallax The Journal of neuroscience : the official journal of the Society for Neuroscience, 2011; 31(47): 17069-73.. Paik Se-Bum, Ringach Dario L Retinal origin of orientation maps in visual cortex Nature neuroscience, 2011; ...
The calcarine fissure (or calcarine sulcus) is an anatomical landmark located at the caudal end of the medial surface of the brain. Its name comes from the Latin calcar meaning spur.. It is a complete sulcus. The calcarine sulcus begins near the occipital pole in two converging rami and runs forward to a point a little below the splenium of the corpus callosum, where it is joined at an acute angle by the medial part of the parietooccipital sulcus. The anterior part of this fissure gives rise to the prominence of the calcar avis in the posterior cornu of the lateral ventricle. The calcarine sulcus is where the primary visual cortex (V1) is concentrated. The central visual field is located in the posterior portion of the calcarine sulcus and the peripheral visual field in the anterior portion. ...
CiteSeerX - Scientific documents that cite the following paper: Antibody labeling of functional subdivisions in visual cortex: cat-301 immunoreactivity in striate and extrastriate cortex of the macaque. Vis Neurosci. 5:67--81
Matrix metalloproteinases play a crucial role in adult visual plasticity in the brains of healthy and stroke-affected mice and their activity has to be within a narrow window for experience-induced plasticity to occur.
Color perception in macaque monkeys and humans depends on the visually evoked activity in three cone photoreceptors and on neuronal post-processing of cone signals. Neuronal post-processing of cone signals occurs in two stages in the pathway from retina to the primary visual cortex. The first stage, in in P (midget) ganglion cells in the retina, is a single-opponent subtractive comparison of the cone signals. The single-opponent computation is then sent to neurons in the Parvocellular layers of the Lateral Geniculate Nucleus (LGN), the main visual nucleus of the thalamus. The second stage of processing of color-related signals is in the primary visual cortex, V1, where multiple comparisons of the single-opponent signals are made. The diversity of neuronal interactions in V1cortex causes the cortical color cells to be subdivided into classes of single-opponent cells and double-opponent cells. Double-opponent cells have visual properties that can be used to explain most of the phenomenology of color
Sensory experience has a profound influence in shaping the functional organization of the cerebral cortex. Over 30 years ago, Hubel and Wiesel described a critical period of postnatal development for the formation of binocular connections in cat visual cortex. They demonstrated that thisconnectivity can be dramatically altered by simple forms of sensory deprivation, such as the temporary closure of one eyelid (monoculardeprivation). Besides the obvious relevance of this neural plasticity to the development of visual capabilities in humans and animals, it seems likely hat similar processes form the basis for some forms of learning and memory in the adult brain. Indeed, visual cortical plasticity, like learning andmemory formation decreases with age and depend on the internal state of the animal. The research in this lab is directed toward elucidating thebasic mechanisms by which visual experience can modify cortical connections in the visual cortex, and how those mechanisms are regulated.. We ...
Home , Papers , Evidence of an increased neuronal activation-to-resting glucose uptake ratio in the visual cortex of migraine patients: a study comparing FDG-PET and visual evoked potentials. ...
Purpose: Patients with early onset retinal dysfunction have abnormal V1 fMRI responses when passively viewing a stimulus. In contrast, patients with adult onset dysfunction do not have significant V1 responses unless they are engaged in a demanding task (Masuda et al., 2008). The development of abnormal cortical responses appears to depend on the timing of the onset of retinal dysfunction. To measure the critical period for the development of abnormal V1 responses, we used fMRI in subjects with congenital, critical period onset, and adult onset macular degeneration (MD).. Methods: We recruited MD patients with similar central retinal lesions. The retinal damage deprives a zone in the posterior of V1 of its normal input projections. We refer to this as the lesion projection zone, LPZ. In the MD and healthy controls we used moving-bar stimuli and a model-based analytical method (Dumoulin and Wandell, 2008) to measure visual field maps and population receptive field (pRF) sizes. We made the ...
TY - JOUR. T1 - Subcellular Localization of Intercellular Adhesion Molecule-5 (Telencephalin) in the Visual Cortex Is Not Developmentally Regulated in the Absence of Matrix Metalloproteinase-9. AU - Kelly, Emily A.. AU - Tremblay, Marie-Eve. AU - Gahmberg, Carl G.. AU - Tian, Li. AU - Majewska, Ania K.. PY - 2014. Y1 - 2014. KW - ICAM-5. KW - dendrite. KW - electron microscopy. KW - plasticity. KW - telencephalin. KW - MMP-9. KW - LONG-TERM POTENTIATION. KW - MATRIX METALLOPROTEINASES. KW - MEMBRANE GLYCOPROTEIN. KW - NEURONAL GLYCOPROTEIN. KW - LEUKOCYTE ADHESION. KW - RAT HIPPOCAMPUS. KW - BRAIN. KW - EXPRESSION. KW - EPHA4. KW - MICROGLIA. KW - 1182 Biochemistry, cell and molecular biology. U2 - 10.1002/cne.23440. DO - 10.1002/cne.23440. M3 - Article. VL - 522. SP - 676. EP - 688. JO - Journal of Comparative Neurology. JF - Journal of Comparative Neurology. SN - 0021-9967. IS - 3. ER - ...
List of causes of Babinskis reflex and Lesions of the visual cortex in children, alternative diagnoses, rare causes, misdiagnoses, patient stories, and much more.
New research is challenging the long-held belief that stroke-induced blindness is untreatable and therefore permanent.. Though speech and motor impairments following stroke are routinely treated with great success, therapies for recovering vision have historically been thought impossible. Many stroke survivors have been consigned to permanent blindness as a result. Fortunately, a new study demonstrates that by stimulating healthy parts of the brain, vision recovery following a stroke is possible.. Krystel Huxlin, Ph.D., a neuroscientist and associate professor at the University of Rochester Eye Institute, helmed the study with seven stroke survivors of various ages who had all suffered severe damage to their primary visual cortex, an area of the brain responsible for making sense of visual stimuli so that a recognizable image can be perceived.. Primary visual cortex damage leaves stroke survivors with a vague awareness of visual stimuli but no way to make sense of what they are seeing or discern ...
Researchers at the Wellcome Trust Centre for Neuroimaging at UCL used non-invasive, real-time brain imaging that enabled participants to watch their own brain activity on a screen, a technique known as neurofeedback. During the training phase, they were asked to try to increase activity in the area of the brain that processes visual information, the visual cortex, by imagining images and observing how their brains responded.. After the training phase, the participants visual perception was tested using a new task that required them to detect very subtle changes in the contrast of an image. When they were asked to repeat this task while clamping brain activity in the visual cortex at high levels, those who had successfully learned to control their brain activity could improve their ability to detect even very small changes in contrast.. This improved performance was only observed when participants were exercising control over their brain activity.. Lead author Dr Frank Scharnowski, who is now ...
Our overarching interest is in the question of how experience and deprivation modify synaptic connections in the brain. Experience-dependent synaptic plasticity is the physical substrate of memory, sculpts connections during postnatal development to determine the capabilities and limitations of brain functions, is responsible for the reorganization of the brain after damage, and is vulnerable in numerous psychiatric and neurological diseases and contributes to their symptoms.. Historically, our major efforts to address this question have been focused on the visual cortex and hippocampus. The visual cortex is a site of robust experience-dependent synaptic plasticity, exemplified by the consequences of temporary monocular deprivation (MD) during childhood. MD sets in motion a stereotyped choreography of synaptic modification whereby the deprived-eye inputs to visual cortex rapidly lose strength and, with a delay, the open-eye inputs undergo a compensatory gain in strength. The behavioral ...
A key research direction in the lab examines visual cortex plasticity in blindness. In sighted primate, much of the occipital lobe is dedicated to visual perception. What happens to this part of the brain when it does not receive its species typical input during development? Previous research finds that in blindness, occipital areas are active during tactile and auditory tasks. One of our goals is to uncover the cognitive functions that are supported by the occipital cortex in blind people. Are these functions similar to vision? We find that in blindness visual areas become involved in higher-cognitive functions, including language, mathematical reasoning and non-verbal executive control. These functions recruit different parts of visual cortex within a single blind individuals. Studying the repurposing of visual cortex for higher-order cognition provides insights into the mechanisms that determine cortical specialization in humans. The lab is interested in how experience changes the ...
While the effects of visual deprivation have been well studied in animal models, much less is known about the effects of blindness on human early visual pathway...
Neuroscience research articles are provided.. What is neuroscience? Neuroscience is the scientific study of nervous systems. Neuroscience can involve research from many branches of science including those involving neurology, brain science, neurobiology, psychology, computer science, artificial intelligence, statistics, prosthetics, neuroimaging, engineering, medicine, physics, mathematics, pharmacology, electrophysiology, biology, robotics and technology. ...
A fundamental property of neuronal circuits is the ability to adapt to altered sensory inputs. It is well established that the functional synaptic changes underlying this adaptation are reflected by structural modifications in excitatory neurons. In contrast, the degree to which structural plasticity in inhibitory neurons accompanies functional changes is less clear. Here, we use two-photon imaging to monitor the fine structure of inhibitory neurons in mouse visual cortex after deprivation induced by retinal lesions. We find that a subset of inhibitory neurons carry dendritic spines, which form glutamatergic synapses. Removal of visual input correlates with a rapid and lasting reduction in the number of inhibitory cell spines. Similar to the effects seen for dendritic spines, the number of inhibitory neuron boutons dropped sharply after retinal lesions. Together, these data suggest that structural changes in inhibitory neurons may precede structural changes in excitatory circuitry, which ...
TY - JOUR. T1 - Attentional control of the processing of neutral and emotional stimuli. AU - Pessoa, Luiz. AU - Kastner, Sabine. AU - Ungerleider, Leslie G.. PY - 2002/12/1. Y1 - 2002/12/1. N2 - A typical scene contains many different objects that compete for neural representation due to the limited processing capacity of the visual system. At the neural level, competition among multiple stimuli is evidenced by the mutual suppression of their visually evoked responses and occurs most strongly at the level of the receptive field. The competition among multiple objects can be biased by both bottom-up sensory-driven mechanisms and top-down influences, such as selective attention. Functional brain imaging studies reveal that biasing signals due to selective attention can modulate neural activity in visual cortex not only in the presence but also in the absence of visual stimulation. Although the competition among stimuli for representation is ultimately resolved within visual cortex, the source of ...
The radial unit hypothesis provides a framework for global (proliferation) and regional (distribution) expansion of the primate cerebral cortex. Using principal component analysis (PCA), we have identified cortical regions with shared variance in their surface area and cortical thickness, respectively, segmented from magnetic resonance images obtained in 23,800 participants. We then carried out meta-analyses of genome-wide association studies of the first two principal components for each phenotype. For surface area (but not cortical thickness), we have detected strong associations between each of the components and single nucleotide polymorphisms in a number of gene loci. The first (global) component was associated mainly with loci on chromosome 17 (9.5e-32 ≤ p ≤ 2.8e-10), including those detected previously as linked with intracranial volume and/or general cognitive function. The second (regional) component captured shared variation in the surface area of the primary and adjacent secondary ...