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1
Remy, Irving. "Les fonctions visuelles rétiniennes et corticales dans les troubles du spectre de la schizophrénie et les situations à risque de psychose." Electronic Thesis or Diss., Strasbourg, 2024. http://www.theses.fr/2024STRAJ030.
Testo completoAbstract (sommario):
Les troubles psychotiques sont caractérisés par d’importantes conséquences fonctionnelles avec des preuves émergentes concernant l’altération des fonctions visuelles de bas niveau. Le lien anatomique et fonctionnel entre la rétine et le cortex visuel a notamment permis d’émettre des hypothèses quant à l’association entre les altérations des deux étages visuels. Nous avons investigué les mesures électrophysiologiques visuelles rétiniennes et corticales dans les troubles du spectre de la schizophrénie et dans les situations à risque de psychose dont l’usage régulier de cannabis et les phases précoces de psychose font partie intégrante. Les résultats ont mentionné des altérations portant sur la plupart des cellules rétiniennes et des déficits au regard du cortex visuel primaire, avec un lien potentiel entre les deux types de mesures dans la schizophrénie. L’intérêt des biomarqueurs électrophysiologiques réside également dans le lien décrit avec les symptômes de la psychose, ce qui incite ainsi à les utiliser davantage en pratique clinique à des fins d’améliorations diagnostiques<br>Psychotic disorders are characterized by severe functional consequences, with emerging evidence of impairment in low-level visual functions. Most notably, the anatomical and functional link between the retina and the visual cortex led to hypotheses concerning the association between alterations in both visual stages. We investigated retinal and cortical visual electrophysiological measurements in schizophrenia spectrum disorders and situations at risk of psychosis, of which regular cannabis use and early phases of psychosis are an integral part. The results highlighted alterations in most retinal cells and deficits in the primary visual cortex, with a potential link between both measures in schizophrenia. The relevance of electrophysiological biomarkers also lies in the link described with psychotic symptoms, motivating them to be used more widely in clinical practice to improve diagnosis
2
Fotheringhame, David K. "Temporal coding in primary visual cortex." Thesis, University of Oxford, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.339357.
Testo completo
3
Nauhaus, Ian Michael. "Functional connectivity in primary visual cortex." Diss., Restricted to subscribing institutions, 2008. http://proquest.umi.com/pqdweb?did=1692099811&sid=1&Fmt=2&clientId=1564&RQT=309&VName=PQD.
Testo completo
4
Thulin, Nilsson Linnea. "The Role of Primary Visual Cortex in Visual Awareness." Thesis, Högskolan i Skövde, Institutionen för biovetenskap, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:his:diva-11623.
Testo completoAbstract (sommario):
Despite its great complexity, a great deal is known about the organization and information-processing properties of the visual system. However, the neural correlates of visual awareness are not yet understood. By studying patients with blindsight, the primary visual cortex (V1) has attracted a lot of attention recently. Although this brain area appears to be important for visual awareness, its exact role is still a matter of debate. Interactive models propose a direct role for V1 in generating visual awareness through recurrent processing. Hierarchal models instead propose that awareness is generated in later visual areas and that the role of V1 is limited to transmitting the necessary information to these areas. Interactive and hierarchical models make different predictions and the aim of this thesis is to review the evidence from lesions, perceptual suppression, and transcranial magnetic stimulation (TMS), along with data from internally generated visual awareness in dreams, hallucinations and imagery, this in order to see whether current evidence favor one type of model over the other. A review of the evidence suggests that feedback projections to V1 appear to be important in most cases for visual awareness to arise but it can arise even when V1 is absent.
5
Krug, Kristine. "Ordering geniculate input into primary visual cortex." Thesis, University of Oxford, 1997. https://ora.ox.ac.uk/objects/uuid:b342ffae-4a31-4171-94a6-83cb516e83fe.
Testo completoAbstract (sommario):
Precise point-to-point connectivity is the basis of ordered maps of the visual field in the brain. One point in the visual field is represented at one locus in the dLGN and one locus in primary visual cortex. A fundamental problem in the development of most sensory systems is the creation of the topographic projections which underlie these maps. Mechanisms ranging from ordered ingrowth of fibres, through chemical guidance of axons to sculpting of the map from an early exuberant input have been proposed. However, we know little about how ordered maps are created beyond the first relay. What we do know is that a topological mismatch requires the exchange of neighbours in the geniculo-cortical projection and that manipulating the input to the primary relay can affect the geniculo-cortical topography. Taking advantage of the immaturity of the newborn hamsterâs visual system, I studied the generation of an ordered map in primary visual cortex during the time of target innervation in normal and manipulated animals. I also investigated the patterning of neuronal activity prior to natural eye-opening. Paired injections of retrograde fluorescent tracers into visual cortex reveal that geniculate fibres are highly disordered at the time of invasion of the cortical plate. Topography in the geniculo-cortical projection emerges out of an unordered projection to area 17 in the first postnatal week. Furthermore, I show that manipulating the peripheral input can alter the topographic map which arises out of the early scatter. Removal of one eye at birth appears to slow the process of geniculo-cortical map formation ipsilateral to the remaining eye and at the end of the second postnatal week, a double projection between thalamus and cortex has formed. If retinal activity is blocked during this time, this double projection does not emerge. The results implicate retinal activity as the signal that induces the development of a different topographic order in the geniculo-cortical projection. It is generally believed that visual experience can influence development only after eye-opening. However, the final part of my thesis shows that neurons in the developing visual cortex of the ferret can not only be visually driven at least 10 days before natural eye-opening, but are also selective for differently oriented gratings presented <i>through the closed eye-lid</i>. Thus, visually-driven neuronal activity could influence development much earlier than previously assumed in many developmental studies.
6
Hesam, Shariati Nastaran. "A functional model for primary visual cortex." Thesis, The University of Sydney, 2012. http://hdl.handle.net/2123/8753.
Testo completoAbstract (sommario):
Many neurons in mammalian primary visual cortex have properties such as sharp tuning for contour orientation, strong selectivity for motion direction, and insensitivity to stimulus polarity, that are not shared with their sub-cortical counterparts. Successful models have been developed for a number of these properties but in one case, direction selectivity, there is no consensus about underlying mechanisms. This thesis describes a model that accounts for many of the empirical observations concerning direction selectivity. The model comprises a single column of cat primary visual cortex and a series of processing stages. Each neuron in the first cortical stage receives input from a small number of on-centre and off-centre relay cells in the lateral geniculate nucleus. Consistent with recent physiological evidence, the off-centre inputs to cortex precede the on-centre inputs by a small interval (~4 ms), and it is this difference that confers direction selectivity on model neurons. I show that the resulting model successfully matches the following empirical data: the proportion of cells that are direction selective; tilted spatiotemporal receptive fields; phase advance in the response to a stationary contrast-reversing grating stepped across the receptive field. The model also accounts for several other fundamental properties. Receptive fields have elongated subregions, orientation selectivity is strong, and the distribution of orientation tuning bandwidth across neurons is similar to that seen in the laboratory. Finally, neurons in the first stage have properties corresponding to simple cells, and more complex-like cells emerge in later stages. The results therefore show that a simple feed-forward model can account for a number of the fundamental properties of primary visual cortex.
7
Rudiger, Philipp John Frederic. "Development and encoding of visual statistics in the primary visual cortex." Thesis, University of Edinburgh, 2017. http://hdl.handle.net/1842/25469.
Testo completoAbstract (sommario):
How do circuits in the mammalian cerebral cortex encode properties of the sensory environment in a way that can drive adaptive behavior? This question is fundamental to neuroscience, but it has been very difficult to approach directly. Various computational and theoretical models can explain a wide range of phenomena observed in the primary visual cortex (V1), including the anatomical organization of its circuits, the development of functional properties like orientation tuning, and behavioral effects like surround modulation. However, so far no model has been able to bridge these levels of description to explain how the machinery that develops directly affects behavior. Bridging these levels is important, because phenomena at any one specific level can have many possible explanations, but there are far fewer possibilities to consider once all of the available evidence is taken into account. In this thesis we integrate the information gleaned about cortical development, circuit and cell-type specific interactions, and anatomical, behavioral and electrophysiological measurements, to develop a computational model of V1 that is constrained enough to make predictions across multiple levels of description. Through a series of models incorporating increasing levels of biophysical detail and becoming increasingly better constrained, we are able to make detailed predictions for the types of mechanistic interactions required for robust development of cortical maps that have a realistic anatomical organization, and thereby gain insight into the computations performed by the primary visual cortex. The initial models focus on how existing anatomical and electrophysiological knowledge can be integrated into previously abstract models to give a well-grounded and highly constrained account of the emergence of pattern-specific tuning in the primary visual cortex. More detailed models then address the interactions between specific excitatory and inhibitory cell classes in V1, and what role each cell type may play during development and function. Finally, we demonstrate how these cell classes come together to form a circuit that gives rise not only to robust development but also the development of realistic lateral connectivity patterns. Crucially, these patterns reflect the statistics of the visual environment to which the model was exposed during development. This property allows us to explore how the model is able to capture higher-order information about the environment and use that information to optimize neural coding and aid the processing of complex visual tasks. Using this model we can make a number of very specific predictions about the mechanistic workings of the brain. Specifically, the model predicts a crucial role of parvalbumin-expressing interneurons in robust development and divisive normalization, while it implicates somatostatin immunoreactive neurons in mediating longer range and feature-selective suppression. The model also makes predictions about the role of these cell classes in efficient neural coding and under what conditions the model fails to organize. In particular, we show that a tight coupling of activity between the principal excitatory population and the parvalbumin population is central to robust and stable responses and organization, which may have implications for a variety of diseases where parvalbumin interneuron function is impaired, such as schizophrenia and autism. Further the model explains the switch from facilitatory to suppressive surround modulation effects as a simple by-product of the facilitating response function of long-range excitatory connections targeting a specialized class of inhibitory interneurons. Finally, the model allows us to make predictions about the statistics that are encoded in the extensive network of long-range intra-areal connectivity in V1, suggesting that even V1 can capture high-level statistical dependencies in the visual environment. The final model represents a comprehensive and well constrained model of the primary visual cortex, which for the first time can relate the physiological properties of individual cell classes to their role in development, learning and function. While the model is specifically tuned for V1, all mechanisms introduced are completely general, and can be used as a general cortical model, useful for studying phenomena across the visual cortex and even the cortex as a whole. This work is also highly relevant for clinical neuroscience, as the cell types studied here have been implicated in neurological disorders as wide ranging as autism, schizophrenia and Parkinson’s disease.
8
De, Pasquale Roberto. "Visual discrimination learning and LTP-like changes in primary visual cortex." Doctoral thesis, Scuola Normale Superiore, 2009. http://hdl.handle.net/11384/85939.
Testo completo
9
Spacek, Martin A. "Characterizing patches of primary visual cortex with minimal bias." Thesis, University of British Columbia, 2015. http://hdl.handle.net/2429/53975.
Testo completoAbstract (sommario):
The brain is highly complex, and studying it requires simplifying experiments, analyses, and theories. New techniques can capture more of the brain's complexity while reducing biases in our understanding of how it works. This thesis describes experiments in primary visual cortex of anesthetized cat, using high-density silicon multisite electrodes to simultaneously record from as many neurons as possible across all cortical layers, thereby characterizing local cortical populations with minimal bias. Recordings were maintained for many hours at a time, and included both spontaneous and stimulus-evoked periods, with a wide variety of naturalistic and artificial visual stimuli. A new "divide-and-conquer" spike sorting method translated correlated multisite voltages into action potentials of spatially localized, isolated neurons. This method tracked neurons over periods of many hours despite drift, and distinguished neurons with firing rates < 0.05 Hz. Neuron physiology was reasonably normal and mostly agreed with accepted principles of visual cortex, but there were exceptions. Surprisingly, firing rates across the population followed a lognormal distribution, and 82% of neurons had mean firing rates < 1 Hz. Also surprisingly, orientation tuning strength across the population was inversely correlated with log firing rate. Finally, there was evidence for neural shift work: over long durations, as some neurons became silent, others became active. To break down analyses by cell type, neurons were classified by their temporal spike shape and receptive field. Responses to repeated natural scene movie clips consisted of unique patterns of remarkably sparse, temporally precise (20 ms wide), reliable events. Mean pairwise correlations between neurons, as measured between trial-averaged responses to natural scene movies, were weakly positive. Correlations between simple and complex cells were lower — and between complex cells were higher — than expected, challenging the hierarchical model of complex cells. Cortical state was classified according to the local field potential, revealing greater natural scene movie response precision, sparseness, and reliability during the synchronized than desynchronized cortical state, contrary to reports in rodents. The open-ended, inclusive, high-dimensional experiments and analyses described here make few assumptions, potentially leading to more insightful theories of brain function than hypothesis-driven research alone.<br>Medicine, Faculty of<br>Graduate
10
Ranson, Adam. "Development and plasticity of the mouse primary visual cortex." Thesis, Cardiff University, 2011. http://orca.cf.ac.uk/54216/.
Testo completoAbstract (sommario):
A strain difference was observed in juvenile OD plasticity between C57BL/6J and C57BL/6JOlaHsd mice whereby open eye 'homeostatic' potentiation was completely absent in the C57BL/6JOlaHsd strain. This was accompanied by an absence of dark exposure induced synaptic scaling as measured <italic>ex vivo.</italic> In contrast in adulthood both strains showed comparable open eye potentiation, suggesting a mechanistic difference between juvenile and adult plasticity. Preliminary data suggests that while juvenile open eye potentiation is homeostatic, in adulthood it may be more LTP like and dependent upon CaMKII autophosphorylation.
11
Edwards, Grace. "Predictive feedback to the primary visual cortex during saccades." Thesis, University of Glasgow, 2014. http://theses.gla.ac.uk/5861/.
Testo completoAbstract (sommario):
Perception of our sensory environment is actively constructed from sensory input and prior expectations. These expectations are created from knowledge of the world through semantic memories, spatial and temporal contexts, and learning. Multiple frameworks have been created to conceptualise this active perception, these frameworks will be further referred to as inference models. There are three elements of inference models which have prevailed in these frameworks. Firstly, the presence of internal generative models for the visual environment, secondly feedback connections which project prediction signals of the model to lower cortical processing areas to interact with sensory input, and thirdly prediction errors which are produced when the sensory input is not predicted by feedback signals. The prediction errors are thought to be fed-forward to update the generative models. These elements enable hypothesis driven testing of active perception. In vision, error signals have been found in the primary visual cortex (V1). V1 is organised retinotopically; the structure of sensory stimulus that enters through the retina is retained within V1. A semblance of that structure exists in feedback predictive signals and error signal production. The feedback predictions interact with the retinotopically specific sensory input which can result in error signal production within that region. Due to the nature of vision, we rapidly sample our visual environment using ballistic eye-movements called saccades. Therefore, input to V1 is updated about three times per second. One assumption of active perception frameworks is that predictive signals can update to new retinotopic locations of V1 with sensory input. This thesis investigates the ability of active perception to redirect predictive signals to new retinotopic locations with saccades. The aim of the thesis is to provide evidence of the relevance of generative models in a more naturalistic viewing paradigm (i.e. across saccades). An introduction into active visual perception is provided in Chapter 1. Structural connections and functional feedback to V1 are described at a global level and at the level of cortical layers. The role of feedback connections to V1 is then discussed in the light of current models, which hones in on inference models of perception. The elements of inferential models are introduced including internal generative models, predictive feedback, and error signal production. The assumption of predictive feedback relocation in V1 with saccades is highlighted alongside the effects of saccades within the early visual system, which leads to the motivation and introduction of the research chapters. A psychophysical study is presented in Chapter 2 which provides evidence for the transference of predictive signals across saccades. An internal model of spatiotemporal motion was created using an illusion of motion. The perception of illusory motion signifies the engagement of an internal model as a moving token is internally constructed from the sensory input. The model was tested by presenting in-time (predictable) and out-of-time (unpredictable) targets on the trace of perceived motion. Saccades were initiated across the illusion every three seconds to cause a relocation of predictive feedback. Predictable in-time targets were better detected than the unpredictable out-of-time targets. Importantly, the detection advantage for in-time targets was found 50 – 100 ms after saccade indicating transference of predictive signals across saccade. Evidence for the transfer of spatiotemporally predictive feedback across saccade was supported by the fMRI study presented in Chapter 3. Previous studies have demonstrated an increased activity when processing unpredicted visual stimulation in V1. This activity increase has been related to error signal production as the input was not predicted via feedback signals. In Chapter 3, the motion illusion paradigm used in Chapter 2 was redesigned to be compatible with brain activation analysis. The internal model of motion was created prior to saccade and tested at a post-saccadic retinotopic region of V1. An increased activation was found for spatiotemporally unpredictable stimuli directly after eye-movement, indicating the predictive feedback was projected to the new retinotopic region with saccade. An fMRI experiment was conducted in Chapter 4 to demonstrate that predictive feedback relocation was not limited to motion processing in the dorsal stream. This was achieved by using natural scene images which are known to incorporate ventral stream processing. Multivariate analysis was performed to determine if feedback signals pertaining to natural scenes could relocate to new retinotopic eye-movements with saccade. The predictive characteristic of feedback was also tested by changing the image content across eye-movements to determine if an error signal was produced due to the unexpected post-saccadic sensory input. Predictive feedback was found to interact with the images presented post-saccade, indicating that feedback relocated with saccade. The predictive feedback was thought to contain contextual information related to the image processed prior to saccade. These three chapters provide evidence for inference models contributing to visual perception during more naturalistic viewing conditions (i.e. across saccades). These findings are summarised in Chapter 5 in relation to inference model frameworks, transsacadic perception, and attention. The discussion focuses on the interaction of internal generative models and trans-saccadic perception in the aim of highlighting several consistencies between the two cognitive processes.
12
Liu, Xiaochen. "Modelling Functional Maps and Associated Visual Gamma Activities in the Primary Visual Cortex." Thesis, The University of Sydney, 2022. https://hdl.handle.net/2123/28536.
Testo completoAbstract (sommario):
The mammalian primary visual cortex (V1) has been extensively studied over the last decades to probe the neural mechanisms behind visual perception of elementary visual features such as edges, direction of motion, and colour. Numerous experiments have visualized the ordered arrangement of various functional maps in V1 and measured the neural activity patterns associated with them. However, only a few studies have quantitatively modelled the influences of the spatial structure of the functional maps on the neural activities. Moreover, the experimental maps usually show a great degree of irregularity and contain a large number of neurons, which makes them difficult to describe in analytic forms and computationally inefficient to integrate into quantitative neural models of large scale brain dynamics.
The present work approximates the functional maps of V1 in a compact analytic representation that complies with the main characteristics of the experimental maps, and integrates such map structure into the established neural field model with interacting neural populations to reproduce oscillatory neural activities in V1.
13
Ajina, Sara. "Changes in connectivity, structure and function following damage to the primary visual cortex." Thesis, University of Oxford, 2015. https://ora.ox.ac.uk/objects/uuid:2e274261-c71a-4ad1-82cf-2fe6bbdbf673.
Testo completoAbstract (sommario):
Residual vision, or blindsight, following damage to the primary visual cortex was first identified almost a century ago. However, the mechanism and pathways underlying this ability, as well as the extent of visual function, remain unclear and are a continuing source of speculation. The work presented here goes some way to try to address these questions, investigating 18 patients with V1 damage and homonymous visual field loss acquired in adulthood. Six experimental chapters explore the extent and potential for visual function after V1 damage, and apply novel neuroimaging paradigms and techniques to try to uncover the mechanisms and pathways that might be involved. A combination of psychophysics, functional and structural MRI was used to investigate responses to blind field stimulation in the dorsal and ventral streams. In addition, diffusion MRI tractography was performed and related to psychophysical performance, so that the three main pathways implicated in blindsight could be evaluated. Lastly, a small rehabilitation study was carried out to assess the effect of training in the blind hemifield, and to investigate whether there is any transfer of learning between the dorsal and ventral visual streams. The results from this work reinforce the suggestion that blindsight may be more common than was first thought, and may extend across a number of characteristics involving both visual streams. It is also suggested that visual function need not be completely unconscious, but that certain salient stimuli can elicit both non-visual and crude visual experience. The use of parametric functional imaging paradigms has enabled a number of properties of non-striate inputs to the extrastriate cortex to be revealed. Together with tractography, this points to an important role for the ipsilateral lateral geniculate nucleus in blindsight function. It is hoped that future work will build upon this, and that it may be possible to target these residual pathways in the rehabilitation of patients with V1 damage.
14
Sengpiel, Frank. "Mechanisms of binocular integration in the mammalian primary visual cortex." Thesis, University of Oxford, 1994. https://ora.ox.ac.uk/objects/uuid:e2337b16-966b-4e65-b727-db7cfa956ef6.
Testo completoAbstract (sommario):
Combining the images seen by the two eyes into a single percept is one of the most challenging computational tasks that the visual cortex has to solve. The first stage at which information from the two retinae converges on individual neurons is the primary visual cortex, VI or area 17. Here, I describe anatomical segregation and interocular suppression as two mechanisms for obviating potential interocular conflict. I have studied VI of the common marmoset (Callithrix jacchus), a New World monkey, with both neurophysiological and anatomical methods. Although similar in most respects to VI of the Old World macaque, layer 4 of the normal adult marmoset has a predominance of binocular cells which corresponds to a lack of segregation of geniculo-cortical afferents into ocular dominance (OD) columns. Brief early monocular deprivation (MD) causes a physiological shift in OD towards the open eye, even when followed by long-term binocular recovery. Two marmosets subjected to 3 weeks of MD from 3 weeks of age exhibited clear afferent segregation in at least parts of VI. Brief disruption of correlated binocular inputs may have served to preserve, and probably enhance the normally transient columnar OD pattern of juvenile marmosets. I have analysed responses of single neurons in cat area 17 to binocular stimuli under conditions that result in perceptual suppression of vision in one eye in humans. In normal animals, a paradigm of binocular contour rivalry was tested. The response of a binocular cell in VI to an optimally oriented grating in one eye is powerfully depressed when gratings of very different orientation are suddenly presented to the other eye, while contours of matching orientation cause the well-known disparity-selective facilitation. However, neuronal responses to persistent rivalrous stimuli do not often exhibit spontaneous alternations between states of dominance and suppression, which might be expected in view of alternations of perceptual dominance in humans under such conditions. Whether or not suppression is triggered by rivalrous contours depends on the immediate history of visual stimulation. Binocular responses are consistently depressed below monocular control levels only when stimulation through one eye with contours of inappropriate orientation is preceded by stimulation of the other eye with a grating of optimum orientation, while there is no suppression with simultaneous stimulus onset: thus neurons display interocular control of responsiveness. In most squinting humans, single vision is maintained through unilateral or alternating suppression. In cats and monkeys that have been rendered strabismic early in life, dominant-eye responses of striate cortical neurons to optimum gratings are dramatically reduced when gratings of any orientation, whether matching or orthogonal, are presented to the non-dominant eye. Like rivalrous suppression in normal animals, this phenomenon is characterized by independence of disparity, broad spatial frequency tuning and dependence on the sequence of stimulation. I propose that reciprocal inhibition between neighbouring ocular dominance columns in VI, over a number of orientation domains, mediates interocular suppression in both normal and strabismic subjects, vetoing signals from one eye in situations that would otherwise cause double vision and confusion.
15
Schulz, D. P. A. "The structure of functional connectivity in cat primary visual cortex." Thesis, University College London (University of London), 2013. http://discovery.ucl.ac.uk/1394406/.
Testo completoAbstract (sommario):
The key to understanding how the brain works is to understand the computations it performs. The structure of anatomical and functional connectivity determines what the brain can compute and how it does so. Correlations have served as a tool for analysing connectivity for over five decades. The mammalian visual cortex has become the most intensively researched cortical area and is unmatched for our knowledge of its anatomical layout and, most importantly, stimulus selectivity. Furthermore, recent perspectives on correlations have arisen from information theory and network models of the brain. The purpose of this dissertation is to determine the precise structure of functional connectivity in cat primary visual cortex. We aim to contribute to and extend previous work by analysing the structure of neural responses and correlations during spontaneous activity, the presentation of artificial stimuli and the presentation of natural stimuli. We report on a comprehensive set of twenty functional and neurophysiological factors, and reveal how previously unexplored factors govern correlations in visual cortex in vivo. Furthermore we find novel functional relationships between factors governing the responses of neurons, and report on a set of properties which allow to distinguish narrow from broad spiking cells. Much attention is devoted to the precise functional dependency of correlations upon firing rate, with the development of methods to remove the firing rate modulation. We show that timescale is an important determinant of correlations, and that natural stimuli generate different correlations than artificial stimuli. We also show that during spontaneous activity, neurons are more likely to fire together if they are tuned to a similar orientation. These results emphasize that both spontaneous and stimulus driven cortical activity contain rich structure that is far from a decorrelated state.
16
Berga, Garreta David. "Understanding eye movements: psychophysics and a model of primary visual cortex." Doctoral thesis, Universitat Autònoma de Barcelona, 2019. http://hdl.handle.net/10803/667901.
Testo completoAbstract (sommario):
En aquesta tesi intentaré explicar (1) com movem els ulls, (2) com fer màquines que entenguin la informació
visual i executar moviments oculars, i (3) com fer que aquestes màquines entenguin tasques per tal de decidir
per aquets moviments oculars.
(1) Hem analitzat del comportament dels moviments oculars provocat per les diferències de característiques
de baix nivell amb una base de dades d’imatges composada per 230 patrons generats sintèticament. S’han
generat un total de 15 tipus d’estímuls (p.e. orientació, brillantor, color, tamany, etc.), amb 7 contrastos per
cada categoría de característica. Les dades de 34 participants s’han pogut col leccionar a partir d’un seguidor
ocular durant la visualització de la base de dades, amb les tasques d’Observació Lliure i Cerca Visual. Els
resultats han mostrat que la saliency és predominantment i distinctivament influenciada per: 1. el tipus de
característica, 2. el contrast de característiques, 3. la temporalitat de les fixacions, 4. la dificultat de la tasca
i 5. l’esbiaixament central. A partir d’aquesta base de dades (SID4VAM) hem computat una comparació
dels models de saliency testejant el seu rendiment utilitzant patrons psicofísics. El nostre estudi revela que
els models en l’estat de l’art en saliency basats Deep Learning no tenen bon rendiment amb patrons sintètics,
contràriament, els models d’inspiració Espectral/Fourier en superen el rendiment i són més consistents amb la
experimentació psicofísica.
(2) Les computacions de l’escorça visual primària (area V1 o escorça estriada) s’han hipotetitzat com a
responsables, entre altres mecanismes de processament visual, de l’atenció visual bottom-up (o també anomenada
saliency). Per tal de validar aquesta hipòtesi, s’han processat diferents bades de dades d’imatges amb
seguidor ocular a partir d’un model biològicament plausible de V1 (anomenat Neurodyamic Saliency Wavelet
Model o NSWAM). Seguint el model neurodinàmic de Li, hem definit les connexions laterals de V1 amb una
xarxa de neurones firing rate, sensitives a característiques visuals com la brillantor, el color, la orientació i la
escala. Els processos subcorticals inferiors (i.e. retinals i talàmics) s’han modelitzat funcionalment. Els mapes
de saliency resultats s’han generat a partir de la sortida del model, representant l’activitat neuronal de V1
cap a les arees del cervell involucrades en el control dels moviments oculars. Fa falta destacar que la nostra
arquitectura unificada és capaç de reproduir diferents processos de la visió (i.e. inducció de brillantor, cromàtica
i malestar visual) sense aplicar cap tipus d’entrenament ni optimització i seguint la mateixa parametrització.
S’ha extès el model (NSWAM-CM) incluint una implementació de la magnificació cortical per tal de definir
les projeccions retinotòpiques cap a V1 per cada visualització de la escena. També s’ha proposat la inhibició
de retorn i mecanismes de selecció per tal de predir l’atenció tant en Observació Lliure com Cerca Visual. Els
resultats han demostrat que el model supera en rendiment a altres models biològicament inspirats per a la
predicció de saliency i sequències de saccades, en concret en imatges de sintètiques i de natura.
(3) El priming de tasca és crucial per a la execució de moviments oculars, involucrant interaccions entre arees
cerebrals relacionades amb la conducta orientada a la meta, memòria de treball i de llarg termini en combinació
amb les zones neuronals responsables de processar els estímuls. En l’últim estudi, hem proposat d’extendre el
Selective Tuning Reference Fixation Controller Model, basat en instruccions de tasca (STAR-FCT), describint
noves definicions computacionals de la Memòria de Llarg Termini, l’Executiu de Tasques Visuals i la Memòria
de Treball per a la Tasca. A partir d’aquests mòduls hem sigut capaços d’utilitzar instruccions textuals per tal
de guiar el model a dirigir la atenció a categoríes específiques d’objecte i/o llocs concrets de la escena. Hem
disenyat el nostre model de memòria a partir de una jerarquía de característiques tant d’alt com de baix nivell.
La relació entre les instruccions executives de la tasca i les representacions de la memòria s’han especificat
utilitzant un arbre de similaritats semàntiques entre les característiques apreses i les anotacions de categoría
d’objecte. Els resultats en comparació amb la saliency han mostrat que utilitzant aquest model, tant els mapes
de localització d’objecte com les prediccions de saccades tenen major probabilitat de caure en les regions salients
depenent de les instruccions.<br>In this thesis we try to explain (1) how we move our eyes, (2) how to build machines that understand visual
information and deploy eye movements, and (3) how to make these machines understand tasks in order to decide
for eye movements.
(1) We provided the analysis of eye movement behavior elicited by low-level feature distinctiveness with a
dataset of 230 synthetically-generated image patterns. A total of 15 types of stimuli has been generated (e.g.
orientation, brightness, color, size, etc.), with 7 feature contrasts for each feature category. Eye-tracking data
was collected from 34 participants during the viewing of the dataset, using Free-Viewing and Visual Search task
instructions. Results showed that saliency is predominantly and distinctively in
uenced by: 1. feature type, 2.
feature contrast, 3. temporality of xations, 4. task di culty and 5. center bias. From such dataset (SID4VAM),
we have computed a benchmark of saliency models by testing performance using psychophysical patterns. Our
study reveals that state-of-the-art Deep Learning saliency models do not perform well with synthetic pattern
images, instead, models with Spectral/Fourier inspiration outperform others in saliency metrics and are more
consistent with human psychophysical experimentation.
(2) Computations in the primary visual cortex (area V1 or striate cortex) have long been hypothesized
to be responsible, among several visual processing mechanisms, of bottom-up visual attention (also named
saliency). In order to validate this hypothesis, images from eye tracking datasets have been processed with
a biologically-plausible model of V1 (named Neurodynamic Saliency Wavelet Model or NSWAM). Following
Li's neurodynamic model, we de ne V1's lateral connections with a network of ring-rate neurons, sensitive
to visual features such as brightness, color, orientation and scale. Early subcortical processes (i.e. retinal
and thalamic) are functionally simulated. The resulting saliency maps are generated from the model output,
representing the neuronal activity of V1 projections towards brain areas involved in eye movement control. We
want to pinpoint that our uni ed computational architecture is able to reproduce several visual processes (i.e.
brightness, chromatic induction and visual discomfort) without applying any type of training or optimization
and keeping the same parametrization. The model has been extended (NSWAM-CM) with an implementation
of the cortical magni cation function to de ne the retinotopical projections towards V1, processing neuronal
activity for each distinct view during scene observation. Novel inhibition of return and selection mechanisms
are also proposed to predict attention in Free-Viewing and Visual Search conditions. Results show that our
model outpeforms other biologically-inpired models of saliency prediction as well as to predict visual saccade
sequences, speci cally for nature and synthetic images.
(3) Task priming has been shown to be crucial to the deployment of eye movements, involving interactions
between brain areas related to goal-directed behavior, working and long-term memory in combination with
stimulus-driven eye movement neuronal correlates. In our latest study we proposed an extension of the Selective
Tuning Attentive Reference Fixation Controller Model based on task demands (STAR-FCT), describing novel
computational de nitions of Long-Term Memory, Visual Task Executive and Task Working Memory. With
these modules we are able to use textual instructions in order to guide the model to attend to speci c categories
of objects and/or places in the scene. We have designed our memory model by processing a visual hierarchy
of low- and high-level features. The relationship between the executive task instructions and the memory
representations has been speci ed using a tree of semantic similarities between the learned features and the
object category labels. Results reveal that by using this model, the resulting object localization maps and
predicted saccades have a higher probability to fall inside the salient regions depending on the distinct task
instructions compared to saliency.
17
Howarth, Christopher. "Pattern adaptation and its interocular transfer in the primary visual cortex." Thesis, Cardiff University, 2008. http://orca.cf.ac.uk/54710/.
Testo completoAbstract (sommario):
Adaptation to a high contrast grating temporarily reduces the contrast sensitivity of neurons in the primary visual cortex (VI). If this adaptation is induced in one eye and the contrast tested with the other a partial transfer of the after-effect is produced, known as interocular transfer (IOT). Intrinsic hyperpolarisation of a cells membrane explains most of this effect, but not the orientation selective nature of adaptation. Optical imaging of intrinsic signals in anaesthetised cats and tree shrews was used to visualise orientation selective responses in VI before and after brief and chronic adaptation. Short term adaptation was achieved with drifting gratings of 12.5 or 50% contrast and fixed orientation (0). Three 1-sec flashes of a 100% contrast grating were used as test stimuli. 8 orientation domains were created according to orientation preference, determined on the basis of pre-adaptation orientation maps. 8 oriented test stimulus responses for each domain were obtained from the absorption signal time course averaged over all pixels. Orientation tuning curves comparable to those in single-cell experiments were produced for the orientation selective pixel populations. A region specific reduction in response was seen in the tuning curves such that responses to 0 were reduced most strongly in regions responding best to 0. An additional stimulus specific reduction was observed in responses to 6, even if 0 wasn't the optimal orientation for a domain. Chronic adaptation was induced with 1 hour of drifting sinusoidal grating in tree shrews. In contrast to a similar experiment in the cat, no alteration in the functional layout of the orientation map was observed. Extracellular recording of IOT in the cat primary visual cortex was performed to elucidate its physiological substrate. Orientation tuning curves were recorded before and after left or right eye adaptation with a 25% or 50% contrast drifting grating with the cells preferred orientation and spatial frequency. Cells were <italic>a priori</italic> categorised according to the binocularity of their control responses. Surprisingly, significant levels of IOT were observed in virtually all monocular cells. Only a weak link was found between ocular dominance and IOT in the full cell population. However, a moderate link between OD and IOT was seen in simple cells. An increase in the response to orthogonal stimuli was also seen in both monocular and binocular cells after adaptation with the non-dominant eye. A subset of complex cells did not display any IOT when adapting with the non-dominant eye and testing with the dominant eye.
18
Cottam, J. C. H. "The role of interneurons in sensory processing in primary visual cortex." Thesis, University College London (University of London), 2013. http://discovery.ucl.ac.uk/1402363/.
Testo completoAbstract (sommario):
Cortical networks are comprised of a multitude of cell types. To understand sensory processing, the function and interaction of these cell types must be investigated. Neurons can be separated into two main groups: excitatory pyramidal (Pyr) cells and inhibitory interneurons. Inhibitory interneurons make up 20% of the total cortical neuronal population and they exhibit a striking array of molecular, morphological and electrophysiological characteristics. The most numerous are the parvalbumin-expressing (PV+) interneurons, accounting for 35-40% of the interneuron population in adult mouse visual cortex. Somatostatin-expressing (SOM+) neurons are another significant group, comprising 20-25% of the interneuron population. The visual responses of SOM+ and PV+ interneurons were measured using 2-photon targeted cell-attached recordings and compared with Pyr cells in the primary visual cortex of anaesthetized mice. These interneuron populations exhibited higher firing rates than Pyr cells in response to oriented gratings, but were less orientation selective, with PV+ interneurons exhibiting the lowest orientation selectivity. Next, SOM+ interneurons were stimulated optogenetically using channelrhodopsin to measure their effect on Pyr cell and PV+ interneuron responses to visual stimuli. Activating small numbers of SOM+ interneurons in vivo inhibited stimulus- evoked firing in PV+ interneurons but not in Pyr cells. Stimulating a large number of SOM+ interneurons confirmed this differential effect, inhibiting PV+ interneurons twice as effectively as Pyr cells. Moreover, the remaining responses to oriented gratings in PV+ cells were more orientation-tuned and time-modulated. In short, inhibitory SOM+ cell activity does not summate with PV+ cell activity, but suppresses it, reconfiguring the inhibitory input to Pyr cells. These results suggest a new role for SOM+ cells, which are activated more slowly and provide dendritic inhibition to Pyr cells while strongly antagonizing PV+ cells, thereby shifting inhibitory input to Pyr cells from somatic to dendritic inhibition throughout the course of the network's visual response.
19
Ko, H. "Functional specificity of local synaptic connections in the primary visual cortex." Thesis, University College London (University of London), 2012. http://discovery.ucl.ac.uk/1344050/.
Testo completoAbstract (sommario):
The capacity of the neocortex to process sensory stimuli relies on interactions between millions of neurons connected by trillions of synaptic connections in dedicated networks. If we are to understand how the brain represents external input, we must study the principles of neuronal interaction at the network level, and this requires us to uncover how connectivity between neurons relates to their function. To investigate the connectivity-function relationship, we developed a novel experimental approach to reveal the functional specificity of local synaptic connections between different cell types in layer 2/3 (L2/3) of the mouse primary visual cortex (V1). For pyramidal cells (PCs), connection probability was related to the similarity of visually driven neuronal activity. PCs with the same preference for oriented stimuli, or responding similarly to naturalistic stimuli formed connections at higher rates than those with dissimilar visual responses. This point to the existence of fine-scale PC subnetworks dedicated to processing related sensory information. In contrast to PCs, parvalbumin expressing/fast spiking (PV/FS) interneurons received dense inputs from surrounding PCs with diverse feature selectivities. PC to PV/FS interneuron connections were an order of magnitude stronger than connections between PCs. This provides a mechanistic explanation for the broad orientation tuning of most PV/FS interneurons. On the other hand, PV/FS interneurons provided divergent outputs to surrounding PCs. To relate the patterns of synaptic connectivity to network activity, we studied how patterns of neuronal co-activation are structured by visual stimuli with different statistical features. Among PC populations, patterns of neuronal correlations were largely stimulus-dependent, indicating that their responses were not strongly dominated by the functionally biased recurrent connectivity. In contrast, visual stimulation only weakly modified co-activation patterns of PV/FS cells, consistent with the observation that these broadly tuned interneurons received very dense and strong synaptic input from nearby PCs with diverse feature selectivities.
20
Stevens, Jean-Luc Richard. "Spatiotemporal properties of evoked neural response in the primary visual cortex." Thesis, University of Edinburgh, 2018. http://hdl.handle.net/1842/31330.
Testo completoAbstract (sommario):
Understanding how neurons in the primary visual cortex (V1) of primates respond to visual patterns has been a major focus of research in neuroscience for many decades. Numerous different experimental techniques have been used to provide data about how the spatiotemporal patterns of light projected from the visual environment onto the retina relate to the spatiotemporal patterns of neural activity evoked in the visual cortex, across disparate spatial and temporal scales. However, despite the variety of data sources available (or perhaps because of it), there is still no unified explanation for how the circuitry in the eye, the subcortical visual pathways, and the visual cortex responds to these patterns. This thesis outlines a research project to build computational models of V1 that incorporate observations and constraints from an unprecedented range of experimental data sources, reconciling each data source with the others into a consistent proposal for the underlying circuitry and computational mechanisms. The final mechanistic model is the first one shown to be compatible with measurements of: (1) temporal firing-rate patterns in single neurons over tens of milliseconds obtained using single-unit electrophysiology, (2) spatiotemporal patterns in membrane voltages in cortical tissues spanning several square millimeters over similar time scales, obtained using voltage-sensitive-dye imaging, and (3) spatial patterns in neural activity over several square millimeters of cortex, measured over the course of weeks of early development using optical imaging of intrinsic signals. Reconciling this data was not trivial, in part because single-unit studies suggested short, transient neural responses, while population measurements suggested gradual, sustained responses. The fundamental principles of the resulting models are (a) that the spatial and temporal patterns of neural responses are determined not only by the particular properties of a visual stimulus and the internal response properties of individual neurons, but by the collective dynamics of an entire network of interconnected neurons, (b) that these dynamics account both for the fast time course of neural responses to individual stimuli, and the gradual emergence of structure in this network via activity-dependent Hebbian modifications of synaptic connections over days, and (c) the differences between single-unit and population measurements are primarily due to extensive and wide-ranging forms of diversity in neural responses, which become crucial when trying to estimate population responses out of a series of individual measurements. The final model is the first to include all the types of diversity necessary to show how realistic single-unit responses can add up to the very different population-level evoked responses measured using voltage-sensitive-dye imaging over large cortical areas. Additional contributions from this thesis include (1) a comprehensive solution for doing exploratory yet reproducible computational research, implemented as a set of open-source tools, (2) a general-purpose metric for evaluating the biological realism of model orientation maps, and (3) a demonstration that the previous developmental model that formed the basis of the models in this thesis is the only developmental model so far that produces realistic orientation maps. These analytical results, computational models, and research tools together provide a systematic approach for understanding neural responses to visual stimuli across time scales from milliseconds to weeks and spatial scales from microns to centimeters.
21
Dylda, Evelyn. "Neuronal circuits of experience-dependent plasticity in the primary visual cortex." Thesis, University of Edinburgh, 2018. http://hdl.handle.net/1842/31234.
Testo completoAbstract (sommario):
Our ability to learn relies on the potential of neuronal networks to change through experience. The primary visual cortex (V1) has become a popular system for studying how experience shapes cortical neuronal networks. Experience-dependent plasticity in V1 has been extensively studied in young animals, revealing that experiences in early postnatal life substantially shape neuronal activity in the developing cortex. In contrast, less is known about how experiences modify the representation of visual stimuli in the adult brain. In addition, adult experience-dependent plasticity remains largely unexplored in neurodevelopmental disorders. To address this issue, we established a two-photon calcium imaging set-up, suitable for chronic imaging of neuronal activity in awake-behaving mice. We implemented protocols for the reliable expression of genetically encoded calcium indicators (GCaMP6), for the implantation of a chronic cranial window and for the analysis of chronic calcium imaging data. This approach enables us to monitor the activity of hundreds of neurons across days, and up to 4-5 weeks. We used this technique to determine whether the daily exposure to high-contrast gratings would induce experience-dependent changes in V1 neuronal activity. We monitored the activity of putative excitatory neurons and of three non-overlapping populations of inhibitory interneurons in layer 2/3 of adult mice freely running on a cylindrical treadmill. We compared the results obtained from mice that were exposed daily to either a high-contrast grating or to a grey screen and characterized their neuronal response properties. Our results did not reveal significant differences in neuronal properties between these two groups, suggesting a lack of stimulus-specific plasticity in our experimental conditions. However, we did observe and characterize, in both groups, a wide range of activity changes in individual cells over time. We finally applied the same method to investigate impairments in experience-dependent plasticity in a mouse model of intellectual disability (ID), caused by synaptic GTPase-activating protein (SynGAP) haploinsufficiency. SynGAP haploinsufficiency is a common de novo genetic cause of non-syndromic ID and is considered a Type1 risk for autism spectrum disorders. While the impact of Syngap gene mutations has been thoroughly studied at the molecular and cellular levels, neuronal network deficits in vivo remain largely unexplored. In this study, we compared in vivo neuronal activity before and after monocular deprivation in adult mutant mice and littermate controls. These results revealed differences in baseline network activity between both experimental groups. These impairments in cortical neuronal network activity may underlie sensory and cognitive deficits in patients with Syngap gene mutations.
22
Sawatari, Atomu. "Specificity and diversity of local connections in Macaque primary visual cortex /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 1999. http://wwwlib.umi.com/cr/ucsd/fullcit?p9945775.
Testo completo
23
Zhu, Mengchen. "Sparse coding models of neural response in the primary visual cortex." Diss., Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/53868.
Testo completoAbstract (sommario):
Sparse coding is an influential unsupervised learning approach proposed as a theoretical model of the encoding process in the primary visual cortex (V1). While sparse coding has been successful in explaining classical receptive field properties of simple cells, it was unclear whether it can account for more complex response properties in a variety of cell types. In this dissertation, we demonstrate that sparse coding and its variants are consistent with key aspects of neural response in V1, including many contextual and nonlinear effects, a number of inhibitory interneuron properties, as well as the variance and correlation distributions in the population response. The results suggest that important response properties in V1 can be interpreted as emergent effects of a neural population efficiently representing the statistical structures of natural scenes under resource constraints. Based on the models, we make predictions of the circuit structure and response properties in V1 that can be verified by future experiments.
24
Bauer, Ute. "Computational models of neural circuitry in the macaque monkey primary visual cortex." [S.l.] : [s.n.], 1998. http://deposit.ddb.de/cgi-bin/dokserv?idn=956186947.
Testo completo
25
Çürüklü, Baran. "Layout and function of the intracortical connections within the primary visual cortex /." Västerås : Mälardalen University, 2003. http://www.mrtc.mdh.se/publications/0604.pdf.
Testo completo
26
Mao, Yuting. "The Reorganization of Primary Auditory Cortex by Invasion of Ectopic Visual Inputs." Digital Archive @ GSU, 2012. http://digitalarchive.gsu.edu/biology_diss/112.
Testo completoAbstract (sommario):
Brain injury is a serious clinical problem. The success of recovery from brain injury involves functional compensation in the affected brain area. We are interested in general mechanisms that underlie compensatory plasticity after brain damage, particularly when multiple brain areas or multiple modalities are included. In this thesis, I studied the function of auditory cortex after recovery from neonatal midbrain damage as a model system that resembles patients with brain damage or sensory dysfunction. I addressed maladaptive changes of auditory cortex after invasion by ectopic visual inputs. I found that auditory cortex contained auditory, visual, and multisensory neurons after it recovered from neonatal midbrain damage (Mao et al. 2011). The distribution of these different neuronal responses did not show any clustering or segregation. As might be predicted from the fact that auditory neurons and visual neurons were intermingled throughout the entire auditory cortex, I found that residual auditory tuning and tonotopy in the rewired auditory cortex were compromised. Auditory tuning curves were broader and tonotopic maps were disrupted in the experimental animals. Because lateral inhibition is proposed to contribute to refinement of sensory maps and tuning of receptive fields, I tested whether loss of inhibition is responsible for the compromised auditory function in my experimental animals. I found an increase rather than a decrease of inhibition in the rewired auditory cortex, suggesting that broader tuning curves in the experimental animals are not caused by loss of lateral inhibition.
These results suggest that compensatory plasticity can be maladaptive and thus impair the recovery of the original sensory cortical function. The reorganization of brain areas after recovery from brain damage may require stronger inhibition in order to process multiple sensory modalities simultaneously. These findings provide insight into compensatory plasticity after sensory dysfunction and brain damage and new information about the role of inhibition in cross-modal plasticity. This study can guide further research on design of therapeutic strategies to encourage adaptive changes and discourage maladaptive changes after brain damage, sensory/motor dysfunction, and deafferentation.
27
Wilson, Edward. "Investigating signal cascades promoting activity-dependent neuroplasticity in monkey primary visual cortex." Thesis, McGill University, 2012. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=106492.
Testo completoAbstract (sommario):
The primate visual system represents an ideal model for the study of neural development and activity-dependent neuroplasticity. The final disposition of the visual cortex is based on a genetically determined cellular organization programmed to become influenced by the animal's environment during a critical period in early postnatal development. Thus neural connections are shaped by the sensory experience of the animal. This plasticity of the visual system declines after the closure of the critical window, and while plasticity is still present in mature animals, its strength is greatly diminished. Cortical plasticity can be restored after the closure of the critical period, however, by altering the incoming neural activity to which the network has adapted. For example, preventing light information from reaching the visual system prompts cortical reorganization in infant and adult primates, such that deprived neurons become responsive to input to the open eye. The transcription factor cyclic-AMP response element-binding protein (CREB) is implicated in cellular processes requiring remodeling of cortical circuits. In fact, CREB uses self-directed mechanisms creating functional circuits by responding to fluctuations in neural activity. For this reason, it is not unexpected for CREB to be implicated in the ocular dominance (OD) plasticity that occurs in monkey primary visual cortex following monocular enucleation (ME). Specifically, level of activated CREB (with specific phosphorylation to serine-133) is elevated in response to changes in neural activity in both activity-deprived and non-deprived visual areas. A problem with this observation, unfortunately, is that it fails to explain how CREB can produce a shift in ocular dominance in deprived neurons while those non-deprived neurons undergo no remodeling.New experimental results presented here show a region-specific alteration in the amount of inhibited CREB occurring in response to ME. Additionally, it was found that signal from the critical CREB transcriptional cofactor, TORC1, is restored to a near critical period level in adults after ME. Inhibited CREB was found to increase in deprived regions, while TORC1 increased in non-deprived regions. Taken together, these results raise the possibility that a) differential modulation of CREB residues and cofactor activation may contribute to its ability to produce output that is context specific; and b) OD plasticity requires the imbalance of CREB activation such that CREB is potentiated in the non-deprived ODCs relative to deprived-eye counterparts.<br>Le système visuel du primate constitue un modèle idéal pour l'étude du développement neuronal et de la neuroplasticité dépendante de l'activité. L'organisation finale du cortex visuel est basée sur une organisation cellulaire génétiquement déterminée, programmée pour être influencée par l'environnement de l'animal pendant une période critique du développement post-natal.Ainsi, les connections neuronales sont formées par l'expérience sensorielle de l'animal. La plasticité du système visuel décline après la fin de cette période critique et, bien qu'existante chez les animaux matures, elle est grandement diminuée. Par contre, la plasticité corticale peut être rétablie après la fin de la période critique en altérant l'activité neuronale entrante à laquelle le système s'est adapté. Par exemple, empêcher que l'information reliée à la lumière se rende au système visuel provoque la réorganisation corticale chez les primates en bas âge et adultes, de façon à ce que les neurones privées deviennent réceptives aux entrées provenant de l'œil ouvert.Le facteur de transcription CREB (cAMP Response Element-Binding) contribue aux fonctions cellulaires requises pour le remodelage des circuits corticaux. En fait, en répondant aux variations de l'activité neuronale, CREB utilise des mécanismes autodirigés pour créer des circuits fonctionnels. Pour cette raison, il n'est pas surprenant que CREB soit impliqué dans la plasticité reliée à la dominance oculaire (DO) qui se produit dans le cortex visuel primaire à la suite de l'inactivation monoculaire (IM). Précisément, les niveaux de la forme activée de CREB (phosphorylée au site serine-133) sont élevés en réponse aux changements d'activité neuronale à la fois dans les zones visuelles privées et non privées des entrées provenant de l'oeil. Le problème relié à cette observation est le fait qu'elle n'explique pas pourquoi CREB peut induire un changement de la dominance oculaire chez les neurones privées alors que celles non privées ne sont pas remodelées.Les nouveaux résultats expérimentaux présentés ici démontrent des changements au niveau de la quantité de CREB inhibé suite à l'IM qui sont spécifiques aux zones. De plus, il a été démontré que le signal du cofacteur transcriptionnel critique de CREB, TORC1, est rétabli à un niveau comparable à celui de la période critique chez les adultes après l'IM. Le CREB inhibé était augmenté dans les zones privées, alors que TORC1 était augmenté dans les zones non privées. Ensembles, ces résultats suggèrent que a) la modulation différentielle des résidus de CREB et l'activation de ses cofacteurs pourraient contribuer à son habileté à produire des effets dépendants du contexte et b) la plasticité reliée à la DO nécessite le déséquilibre de l'activation de CREB de façon à ce que CREB est potentialisé dans les zones non-privées comparées aux zones privées.
28
Law, Judith S. "Modeling the development of organization for orientation preference in primary visual cortex." Thesis, University of Edinburgh, 2009. http://hdl.handle.net/1842/3935.
Testo completoAbstract (sommario):
The cerebral cortex of mammals comprises a series of topographic maps, forming sensory and motor areas such as those in the visual, auditory, and somatosensory systems. Understanding the rules that govern the development of these maps and how this topographic organization relates to information processing is critical for the understanding of cortical processing and whole brain function. Previous computational models have shown that topographic maps can develop through a process of self-organization, if spatially localized patches of cortical neurons are activated by particular stimuli. This thesis presents a series of computational models, based on this principle of self-organization, that focus on the development of the map of orientation preference in primary visual cortex (V1). This map is the prototypical example of topographic map development in the brain, and is the most widely studied, however the same self-organizing principles can also apply to maps of many other visual features and maps in many other sensory areas. Experimental evidence indicates that orientation preference maps in V1 develop in a stable way, with the initial layout determined before eye opening. This constraint is at odds with previous self-organizing models, which have used biologically unfounded ad-hoc methods to obtain robust and reliable development. Such mechanisms inherently lead to instability, by causing massive reorganization over time. The first model presented in this thesis (ALISSOM) shows how ad-hoc methods can be replaced with biologically realistic homeostatic mechanisms that lead to development that is both robust and stable. This model shows for the first time how orientation maps can remain stable despite the massive circuit reconstruction and change in visual inputs occurring during development. This model also highlights the requirements for homeostasis in the developing visual circuit. A second model shows how this development can occur using circuitry that is consistent with the known wiring in V1, unlike previous models. This new model, LESI, contains Long-range Excitatory and Short-range Inhibitory connections between model neurons. Instead of direct long-range inhibition, it uses di-synaptic inhibition to ensure that when visual stimuli are at high contrast, long-range excitatory connections have an overall inhibitory influence. The results match previous models in the special case of the high-contrast inputs that drive development most strongly, but show how the behavior relates to the underlying circuitry, and also make it possible to explore effects at a wide range of contrasts. The final part of this thesis explores the differences between rodents and higher mammals that lead to the lack of topographic organization in rodent species. A lack of organization for orientation also implies local disorder in retinotopy, and analysis of retinotopy data from two-photon calcium imaging in mouse (provided by Tom Mrsic- Flogel, University College London) confirms this hypothesis. A self-organizing model is used to investigate how this disorder can arise via variation in either feed-forward connections to V1 or lateral connections within V1, and how the effects of disorder may vary between species. These results suggest that species with and without topographic maps implement similar visual algorithms differing only in the values of some key parameters, rather than having fundamental differences in architecture. Together, these results help us understand how and why neurons develop preferences for visual features such as orientation, and how maps of these neurons are formed. The resulting models represent a synthesis of a large body of experimental evidence about V1 anatomy and function, and offer a platform for developing a more complete explanation of cortical function in future work.
29
Chirimuuta, Mazviita. "A psychophysical and computational study of contrast coding in primary visual cortex." Thesis, University of Cambridge, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.615802.
Testo completo
30
Gajowa, Marta. "Synaptic and cellular mechanisms underlying functional responses in mouse primary visual cortex." Thesis, Sorbonne Paris Cité, 2018. http://www.theses.fr/2018USPCB125.
Testo completoAbstract (sommario):
L'élaboration de l'information dans le cerveau est basée sur les propriétés des neurones qui analysent leurs inputs et génèrent les potentiels d'actions, ainsi que sur un réseau synaptique d'une complexité beaucoup plus importante que ce que l'homme peut créer. Mon projet consiste à étudier ces éléments dans le cortex visuel de la souris, pour décrire comment ils permettent aux neurones de répondre à des caractéristiques du scène visuelle. Je développe des outils optogénétiques pour pouvoir stimuler des neurones individuels in vivo, ce qui va ensuite être intégré avec des mesures de leur réponse visuelle pour déterminer le circuit synaptique fonctionnel Je vais ensuite faire des mesures précises des inputs synaptiques évoqués par les stimuli visuels, suivies des réinjections des reconstructions statistiques de ces inputs dans le même neurone, établir des limites biophysiques permettant de déchiffrer le code neuronal dans des conditions normales et pathologiques<br>Feature selectivity of cortical neurons, one example of functional properties in the brain, is the ability of neurons to respond to particular stimulus attributes - e.g. the receptive field of a neuron in the primary visual cortex (V1) with respect to object movement direction. This thesis contributes to understanding how feature selectivity arises in mouse V1. It is divided into two parts, each based on distinct approaches to elucidate visual processing mechanisms, the first at a population level and the second at the single neuron level. First, on a population level, I have developed tools towards an eventual project that combines 2-photon optogenetics, 2-photon imaging and traditional whole-cell electrophysiology to map functional connectivity in V1. This map will provide a link between cell tuning (i.e. cell function) and network architecture, enabling quantitative and qualitative distinction between two extreme scenarios in which cells in mouse V1 are either randomly connected, or are associated in specialized subnetworks. Here I describe the technical validation of the method, with the main focus on finding the appropriate biological preparation and reagents. Second, based on whole-cell patch recordings of single mouse V1 neurons in vivo, I characterize the neuronal input-output (I/O) transfer function using current and conductance inputs, the latter intended to mimic the biophysical properties of synapses in a functional context. I employ a novel closed-loop in vivo protocol based on a combination of current, voltage and dynamic clamp recording modes. I first measure the basic I/O transfer function of a given neuron with current and conductance steps, under current and dynamic clamp, respectively. I then measure the visually evoked spiking output, under current clamp, and the synaptic conductance input, under voltage clamp, to that neuron. Finally, I reintroduce variations of the visually-evoked conductance input to the same cell under dynamic clamp. In that manner, I describe an I/O transfer function which allows a characterization of the mathematical operations performed by the neuron during functional processing. Furthermore, modifications of the relative scaling and the temporal characteristics of the excitatory and inhibitory components of the reintroduced synaptic input, enables dissection of each component's role in shaping the spiking output, as well as to infer overall differences between various physiological cell types (e.g. regular-adapting, presumably excitatory, versus fast-spiking, presumably inhibitory, neurons). Finally, examination of the transfer functions, in particular their dependence on temporal modifications, provides insights on the relationship between the neuronal code and the biophysical properties of neurons and their network
31
Ball, Christopher Edward. "Modeling the emergence of perceptual color space in the primary visual cortex." Thesis, University of Edinburgh, 2015. http://hdl.handle.net/1842/11694.
Testo completoAbstract (sommario):
Humans’ perceptual experience of color is very different from what one might expect, given the light reaching the eye. Identical patterns of light are often perceived as different colors, and different patterns of light are often perceived as the same color. Even more strikingly, our perceptual experience is that hues are arranged circularly (with red similar to violet), even though single-wavelength lights giving rise to perceptions of red and violet are at opposite ends of the wavelength spectrum. The goal of this thesis is to understand how perceptual color space arises in the brain, focusing on the arrangement of hue. To do this, we use computational modeling to integrate findings about light, physiology of the visual system, and color representation in the brain. Recent experimental work shows that alongside spatially contiguous orientation preference maps, macaque primary visual cortex (V1) represents color in isolated patches, and within those patches hue appears to be spatially organized according to perceptual color space. We construct a model of the early visual system that develops based on natural input, and we demonstrate that several factors interact to prevent this first model from developing a realistic representation of hue. We show these factors as independent dimensions and relate them to problems the brain must be overcoming in building a representation of perceptual color space: physiological and environmental variabilities to which the brain is relatively insensitive (surprisingly, given the importance of input in driving development). We subsequently show that a model with a certain position on each dimension develops a hue representation matching the range and spatial organization found in macaque V1—the first time a model has done so. We also show that the realistic results are part of a spectrum of possible results, indicating other organizations of color and orientation that could be found in animals, depending on physiological and environmental factors. Finally, by analyzing how the models work, we hypothesize that well-accepted biological mechanisms such as adaptation, typically omitted from models of both luminance and color processing, can allow the models to overcome these variabilities, as the brain does. These results help understand how V1 can develop a stable, consistent representation of color despite variabilities in the underlying physiology and input statistics. This in turn suggests how the brain can build useful, stable representations in general based on visual experience, despite irrelevant variabilities in input and physiology. The resulting models form a platform to investigate various adult color visual phenomena, as well as to predict results of rearing experiments.
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Hattori, Ryoma. "Neural Mechanisms Underlying the Establishment of Unimodality in Mouse Primary Visual Cortex." Thesis, Harvard University, 2016. http://nrs.harvard.edu/urn-3:HUL.InstRepos:26718754.
Testo completoAbstract (sommario):
Early visual cortex, an area classically defined as a purely unisensory cortex, has been suggested to be influenced by non-visual sensory inputs (Wallace et al., 2004; Iurilli et al., 2011; Vasconcelos et al., 2011; Charbonneau et al., 2012; Liang et al., 2013) and the cross-modal effects are enhanced after blindness (Bavelier, D. & Neville, 2002; Pascual-Leone et al., 2005). Although ectopic or increased neural projections from non-visual sensory areas might be partly responsible for the enhanced cross-modality after blindness in some cases (Karlen et al., 2006), such mechanism cannot explain acute enhancement of cross-modality after short-term blindfolding (Merabet et al., 2007; Merabet et al., 2008). Here I showed that mouse visual cortex was weakly multimodal even at the primary visual cortex (V1) and the cross-modality drastically shifted around the critical period (CP) for visual functions. I found that sound modulations of visual spiking activities are tri-phasic in V1, and the audiovisual interactions followed inverse effectiveness rule as in classically-defined multisensory areas. The inverse effectiveness impaired orientation and direction selectivity of visual response. Furthermore, I showed that auditory influence on V1 was dampened specifically during the CP through balancing of sound-driven excitation and inhibition. Visual experience regulated the cross-modality through GABAergic inhibition, and both soma-targeting and dendrite-targeting interneurons gated the cross-modal inputs in different ways. Finally, I showed that abnormal cross-modality was a common characteristics among three different autistic mouse models, supporting the comorbidity between autism and synesthesia (Baron-Cohen et al., 2013; Neufeld et al., 2013). In particular, autistic BTBR inbred strain exhibited exceptionally large V1 cross-modal auditory response with vision-like properties. My study suggests that the cross-modality regulation during CP is crucial for V1 to functionally mature as ‘visual’ cortex and failure of it might develop synesthesia-like multisensory V1.<br>Biology, Molecular and Cellular
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Golledge, Huw D. R. "Does inter-columnar neuronal synchrony play a role in visual feature binding?" Thesis, University of Newcastle Upon Tyne, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.323355.
Testo completo
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Bowlsby, Stephen. "Glutathione as a neurotransmitter in primary visual cortex : binding sites and neuronal uptake." Thesis, University of British Columbia, 1991. http://hdl.handle.net/2429/29776.
Testo completoAbstract (sommario):
Understanding the response properties and plasticity of primary visual (striate) cortex depends on the determination of its "chemical circuitry", yet the neurotransmitters that mediate sensory input to striate cortex are not known, and such evidence as exists is contradictory. The geniculpstriate input bears a similarity to glutamatergic neurotransmission, but glutamate is not a good candidate in this pathway. In contrast, glutathione (GSH) has been suggested to be one of the excitatory-amino-acid neurotransmitters in cortex (Ogita and Yoneda, 1987).
Criteria for the identification of a neurotransmitter include the demonstration of the presence of receptors for the substance (necessary) and the demonstration of retrograde uptake and transport of the substance (supportive). The present study attempted to characterize GSH binding sites, examine their distribution, and examine possible GSH interaction with excitatory amino acid receptors in rat and cat primary visual cortex using in-vitro radioligand methods on 20-µm-thick cortex sections. In addition, the present study used in-vivo uptake and transport of radiolabeled tracers to attempt to support the localization of GSH neurotransmission to pathways within the visual system.
Saturation binding experiments using radiolabeled GSH in rat primary occipital cortex sections revealed a high-affinity site (Kd = 5.4 nM; Bmax = 235 fmol/mg protein) and a
denser low-affinity site (Kd = 1.3 µM; Bmax = 1.3 pmol/mg protein) , the Kd of which is typical of excitatory amino acid receptors. Kinetic and competition experiments yielded similar Kd values. Competition studies of the low-affinity GSH binding site showed a separate site as well as binding with affinity for the neurotransmitter candidates cysteine, aspartate, and glutamate. Excitatory-amino-acid receptor subtype affinity was shown for AMPA at pH 7.4 and for NMDA at pH 6.9.. Radiolabeled GSH binding in adult rat visual cortex showed a relatively uniform distribution across all cortical layers. Binding distribution studies in cat striate cortex showed densest [³⁵S]GSH binding in layer 4, the geniculostriate input layer, from 13 days postnatal to adult. Distribution of [³⁵S]GSH binding sites also showed a distinct preference for lower layer 4 in monkey striate cortex.
Microinjection of [³⁵S]GSH, [³H]GSH, and its constituent amino acids, [³H]glutamate, [³⁵S]cysteine, and [³H]glycine, into primary and secondary visual cortex in the rat produced uptake to visual-system thalamic nuclei and superior colliculus. Possible retrograde uptake to cell bodies was determined for [³H]GSH and [³⁵S]cysteine in the dorsal lateral geniculate and lateral posterior nuclei in the rat. Microinjection of [³H]GSH in cat cortical area 17 produced uptake to the dorsal lateral geniculate nucleus, but possible retrograde uptake to cell bodies could not be determined.
These results support the proposition that GSH plays a role as a neurotransmitter in primary visual cortex, in
particular as a geniculostriate neurotransmitter, and may take part in neurotransmission by interacting with excitatory amino acid receptors in addition to GSH receptors.<br>Medicine, Faculty of<br>Cellular and Physiological Sciences, Department of<br>Graduate
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Berger, Denise [Verfasser]. "Intrinsic and functional aspects of neuronal synchrony in primary visual cortex / Denise Berger." Berlin : Freie Universität Berlin, 2009. http://d-nb.info/1023709279/34.
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Freeman, Tobe. "Mechanisms of binocular integration and their development in the cat primary visual cortex." Thesis, University of Oxford, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.267925.
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Revina, Yulia. "Influence of scene surround on cortical feedback to non-stimulated primary visual cortex." Thesis, University of Glasgow, 2017. http://theses.gla.ac.uk/8016/.
Testo completoAbstract (sommario):
Most of the time we are not passively viewing scenes but want to extract behaviourally relevant information. In addition, objects do not often occur in isolation outside the visual scientist’s laboratory but are embedded in complex visual scenes. If the brain is to be adaptive, it needs to process visual information with regards to its context. Thus perception is not purely determined by the specific input to the retina but depends on the surrounding scene, objects, attention, memory, prior knowledge, expectations and predictions. Traditionally, the visual system in the human brain has been viewed as having a hierarchical organisation with signals travelling in one direction: input from the eyes arrives at "lower" order areas, which then transmit their computations to "higher" order areas. As one moves up the hierarchy, visual areas code more complex and more abstract information, and after the final processing stage, the system gives an output. However, in reality things are not so simple. In fact, in the primary visual cortex (V1), which is one of the first visual processing stages in the brain, external stimuli constitute less than 10% of the total input. The rest of the input originates from internal connections, either within V1 itself or via signals arriving from "higher" areas, back down to V1. In this way, "higher" areas can tell "lower" ones about the bigger picture and the neighbouring elements. This internal processing in the brain is the mechanism which provides context and enriches the information reaching us from the external world. The signals arriving to V1 from the retina are referred to as feedforward, while the signals going in the opposite direction, from higher areas back to V1, are called feedback. Each neuron responds to its preferred stimulus in a specific region of the visual field, called the receptive field. Feedforward signals act on the central region of a neuron’s receptive field, while feedback signals act on a larger surround region and thus are able to inform the centre about the surrounding context. However, it is not well established which aspects of the surrounding scene define these contextual interactions. This thesis investigated the influence of the scene surround on feedback to V1. We aimed to establish how the scene surround contributes to informative feedback signals. An introduction about what is already known regarding the function of feedback and the information it transmits is provided in Chapter 1. I give an overview of the previous studies which highlight the various contextual roles of feedback, such as perceptual grouping, contour and object completion, expectation, attention and prediction, as well as being the mechanism allowing visual imagery. Chapter 2 aimed to address whether feedback provides coarse or fine-grained information about the surrounding scene. Since during normal viewing both feedback and feedforward signals are present, we investigated feedback signals in isolation by using a partial occlusion paradigm to remove meaningful feedforward input in a specific region of the scene. We filtered the scene surrounding the occluded region into a fine-grained and a coarse version. We also varied how much information was shared between the fine-grained and coarse version of the same scene. This was done to investigate whether the information feedback carried was tightly tuned to the spatial scale of the surrounding scene, or whether the information it contained was similar across the two types of the scene surround. We found that the feedback contained signals about both coarse and fine-grained surrounds, but there was also some overlap between these feedback signals. In addition, we found that the feedback information did not correspond to a direct "filling-in" of the missing feedforward input, suggesting that feedback and feedforward signals represent the scene in different ways. In Chapter 3 we took a closer look at the amount of meaningful scene surround that is necessary to elicit informative feedback signals. The results showed that increasing the amount of scene information in the surround resulted in more meaningful feedback signals. We confirmed our earlier finding that the feedback information in the occluded region is dissimilar to the corresponding feedforward input when the feedforward region is isolated from the scene surround. Adding the scene surround to the feedforward stimulus increased this feedback/feedforward similarity. Overall, these findings point to the notion that feedback signals combine with feedforward input under normal visual processing. Isolated feedforward input in the absence of the surround provides V1 neurons with impoverished information. Neighbouring elements of the scene or its overall global structure can be sources of context. In Chapter 4 we explored which regions of the scene surround contribute the most to the contextual feedback signals arriving at V1 – is this limited to only local neighbouring regions or does the feedback directly contain information about the overall global image structure, taking into account distant retinotopic regions as well? In the first experiment, we used simple global structures made up of four Gabor elements and showed that such simplistic shapes failed to induce contextual feedback into the occluded region. However, in the presence of feedforward information, we saw that feedback from the local surround combined with identical feedforward input to give rise to different activity patterns in that feedforward region. This suggests that feedback may be recruited differentially depending on whether feedforward stimulation is present or absent. In the second experiment, we used natural scenes and tested whether contextual feedback can originate from a distant retinotopic region in the situation when the local scene surround was not informative. We manipulated scene information in a distant retinotopic region (in the opposite hemisphere) while keeping the local neighbouring surround information the same. The results showed a lack of meaningful feedback in the occluded region, and that feedback from the distant surround had a negligible effect on the identical feedforward information, in contrast to the finding obtained previously with the local surround. These findings suggest that feedback preferentially originates from nearby regions and provides context to disambiguate local feedforward elements. Therefore context about the global scene structure may arise from a series of local surround interactions. Chapter 5 summarises these findings and discusses the overarching themes regarding the content of feedback and its role in full visual processing. At the end, I propose some future research directions.
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Briggs, Farran. "Local circuitry and function of deep layer neurons in monkey primary visual cortex /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 2003. http://wwwlib.umi.com/cr/ucsd/fullcit?p3077804.
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Baker, Pamela Mary. "The contribution of cortical microcircuitry to stimulus masking effects in cat primary visual cortex /." Zürich : ETH, 2008. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=17615.
Testo completo
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Bartsch, Armin P. "Orientation maps in primary visual cortex a Hebbian model of intracortical and geniculocortical plasticity /." [S.l. : s.n.], 2000. http://deposit.ddb.de/cgi-bin/dokserv?idn=962125733.
Testo completo
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Cossell, L. "Functional organization and development of connectivity in L2/3 of mouse primary visual cortex." Thesis, University College London (University of London), 2014. http://discovery.ucl.ac.uk/1435416/.
Testo completoAbstract (sommario):
It is a fundamental goal of neuroscience to understand how feature-selective sensory response properties of cortical neurons emerge from the highly structured synaptic organization of the cortex. This thesis describes the receptive field (RF) organization in L2/3 of mouse primary visual cortex (V1) and the highly specific local circuits from which this organization emerges. We also examine how this connection specificity arises during development. We studied the organization of RFs in mouse V1 using in vivo two-photon calcium imaging. Local populations of neurons had a wide diversity of RFs, which were tightly clustered in visual space, with low scatter and high amounts of overlap. However, a retinotopic organization was observed and the ON and OFF subfields had non-random organization: more pairs of neurons had high subfield overlap, and more pairs of neurons had no subfield overlap, than would be expected by chance. ON subfields were more prevalent than OFF subfields and were more highly scattered in visual space. To relate this RF organization to the underlying neuronal circuitry, we used multiple whole-cell recordings in vitro to assess connections between neurons whose RFs had been mapped in vivo. The incidence and strength of connections were highly correlated with RF similarity. Neurons with spatially matched RFs (i.e. overlapping ON and OFF subfields) connected at high rates, with strong and often bidirectional connections, while neurons with mismatched RFs rarely connected with much weaker connections, despite covering similar regions of visual space. Although only a small fraction of neurons had matched RFs, these neurons formed the strongest connections. Thus, feature-specific information is provided by a small subset of connections that are sufficiently powerful to influence the stimulus selectivity of neuronal responses. To understand the development of functionally-specific connectivity, we performed similar experiments at different postnatal ages. Although responses were highly selective for visual features at eye-opening, neurons responding to similar features were not preferentially connected. After eye-opening, local connectivity reorganized extensively, such that more connections formed between neurons with similar response properties, and connections were lost between visually unresponsive neurons. This work provides insights into the organization of neocortical circuits, which can be used for biologically-informed computational models of the neocortex.
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Houlton, R. E. "Influence of adaptation on single neuron and population coding in mouse primary visual cortex." Thesis, University College London (University of London), 2014. http://discovery.ucl.ac.uk/1417573/.
Testo completoAbstract (sommario):
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 to assess the relative contributions of cortical/subcortical mechanisms towards adaptation in mouse V1, I used optogenetic methods to suppress cortical activity (via activation of Channelrhodopsin-2 in PV interneurons) during an adapting stimulus. Suppressing cortical activity, and hence any activity-dependent cortical mechanisms, largely counteracted the effects of adaptation on neuronal responsiveness, consistent with a substantial cortical component of adaptation. Interestingly, whilst adaptation reduced both contrast and response gain, only the latter effect was influenced by cortical suppression. This suggests that the mechanisms mediating adaptation-induced alterations in contrast and response gain are different, and possibly occur at different loci within the visual pathway. The consequences of adaptation on V1 population responses were explored with two-photon calcium imaging. Adaptation to dynamic stimuli of multiple orientations caused a divisive scaling of responses, consistent with a reduction in response gain. Adaptation also decorrelated neuronal activity, leading to sparser and more distributed stimulus representations across the population. Whole-cell recordings further revealed that these effects were associated with decreased membrane depolarisation, and an increase in membrane potential variability.
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Zeitler, Leo Laurenz. "Functional and Dynamical Consequences of Long-Range Patchy Connections in the Primary Visual Cortex." Thesis, KTH, Skolan för elektroteknik och datavetenskap (EECS), 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-279584.
Testo completoAbstract (sommario):
While it is a known fact that higher mammals develop a differently structured primary visual cortex than rodents, the reason for this phenomenon remains unknown. Eutherian species that rely primarily on vision establish long-range patchy connections between locally clustered neurons. The V1 of rats and mice which use odour as their primary sensory input do not possess such a structural organisation and wiring profile. Albeit existing studies investigating the functional properties of networks with distal patchy connections, the dynamical consequences are still unclear. We hypothesised that the establishment of tuning-specific long-range patchy connections permits a better derivation of missing stimulus statistics from just sparse sampling. Although our results were not able to fully verify these claims, they indicate that locally clustered networks that exhibit tuning-dependent long-range connections enhance predictions based on sophisticated saccadic eye movements and the information aggregation over time and space.<br>Det är känt att högre däggdjur utvecklar ett annorlunda strukturerat syncentrum än gnagare, men anledningarna till detta fenomen är fortfarande okänt. Högre däggdjur som huvudsakligen förlitar sig på syn etablerar långväga kopplingar med lokalt samlad fördelning mellan lokalt koncentrerade neuroner. V1 hos råttor och möss som använder lukt som sitt huvudsakliga sinnesintryck har däremot inte en sådan struktur. Trots befintliga studier som undersöker de funktionella egenskaperna av nätverk med lokalt samlade kopplingar på ytteränden är de dynamiska konsekvenserna fortfarande oklara. Vi skapade en hypotes att upprättandet av long-range patchy connections tillåter en bättre härledning av saknad stimulus statistik från få prov. Våra resultat lyckades inte fullständigt bekräfta dessa antaganden, men de indikerade att lokalt koncentrerade nätverk som uppvisar riktningsanpassade långväga kopplingar förbättrar uppskattningar baserade på komplexa saccadiska ögonrörelser och informationsaggregation över tid och rum.
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Keemink, Sander Wessel. "Coding of multivariate stimuli and contextual interactions in the visual cortex." Thesis, University of Edinburgh, 2018. http://hdl.handle.net/1842/28969.
Testo completoAbstract (sommario):
The primary visual cortex (V1) has long been considered the main low level visual analysis area of the brain. The classical view is of a feedfoward system functioning as an edge detector, in which each cell has a receptive field (RF) and a preferred orientation. Whilst intuitive, this view is not the whole story. Although stimuli outside a neuron’s RF do not result in an increased response by themselves, they do modulate a neuron’s response to what’s inside its RF. We will refer to such extra-RF effects as contextual modulation. Contextual modulation is thought to underlie several perceptual phenomena, such as various orientation illusions and saliency of specific features (such as a contour or differing element). This gives a view of V1 as more than a collection of edge detectors, with neurons collectively extracting information beyond their RFs. However, many of the accounts linking psychophysics and physiology explain only a small subset of the illusions and saliency effects: we would like to find a common principle. So first, we assume the contextual modulations experienced by V1 neurons is determined by the elastica model, which describes the shape of the smoothest curve between two points. This single assumption gives rise to a wide range of known contextual modulation and psychophysical effects. Next, we consider the more general problem of encoding and decoding multi-variate stimuli (such as center surround gratings) in neurons, and how well the stimuli can be decoded under substantial noise levels with a maximum likelihood decoder. Although the maximum likelihood decoder is widely considered optimal and unbiased in the limit of no noise, under higher noise levels it is poorly understood. We show how higher noise levels lead to highly complex decoding distributions even for simple encoding models, which provides several psychophysical predictions. We next incorporate more updated experimental knowledge of contextual modulations. Perhaps the most common form of contextual modulations is center surround modulation. Here, the response to a center grating in the RF is modulated by the presence of a surrounding grating (the surround). Classically this modulation is considered strongest when the surround is aligned with the preferred orientation, but several studies have shown how many neurons instead experience strongest modulation whenever center and surround are aligned. We show how the latter type of modulation gives rise to stronger saliency effects and unbiased encoding of the center. Finally, we take an experimental perspective. Recently, both the presence and the underlying mechanisms of contextual modulations has been increasingly studied in mice using calcium imaging. However, cell signals extracted with calcium imaging are often highly contaminated by other sources. As contextual effects beyond center surround modulation can be subtle, a method is needed to remove the contamination. We present an analysis toolbox to de-contaminate calcium signals with blind source separation. This thesis thus expands our understanding of contextual modulation, predicts several new experimental results, and presents a toolbox to extract signals from calcium imaging data which should allow for more in depth studies of contextual modulation.
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Antolik, Jan. "Unified developmental model of maps, complex cells and surround modulation in the primary visual cortex." Thesis, University of Edinburgh, 2011. http://hdl.handle.net/1842/4875.
Testo completoAbstract (sommario):
For human and animal vision, the perception of local visual features can depend on the spatial arrangement of the surrounding visual stimuli. In the earliest stages of visual processing this phenomenon is called surround modulation, where the response of visually selective neurons is influenced by the response of neighboring neurons. Surround modulation has been implicated in numerous important perceptual phenomena, such as contour integration and figure-ground segregation. In cats, one of the major potential neural substrates for surround modulation are lateral connections between cortical neurons in layer 2/3, which typically contains ”complex” cells that appear to combine responses from ”simple” cells in layer 4C. Interestingly, these lateral connections have also been implicated in the development of functional maps in primary visual cortex, such as smooth, well-organized maps for the preference of oriented lines. Together, this evidence suggests a common underlying substrate the lateral interactions in layer 2/3—as the driving force behind development of orientation maps for both simple and complex cells, and at the same time expression of surround modulation in adult animals. However, previously these phenomena have been studied largely in isolation, and we are not aware of a computational model that can account for all of them simultaneously and show how they are related. In this thesis we resolve this problem by building a single, unified computational model that can explain the development of orientation maps, the development of simple and complex cells, and surround modulation. First we build a simple, single-layer model of orientation map development based on ALISSOM, which has more realistic single cell properties (such as contrast gain control and contrast invariant orientation tuning) than its predecessor. Then we extend this model by adding layer 2/3, and show how the model can explain development of orientation maps of both simple and complex cells. As the last step towards a developmental model of surround modulation, we replace Mexican-hat-like lateral connectivity in layer 2/3 of the model with a more realistic configuration based on long-range excitation and short-range inhibitory cells, extending a simpler model by Judith Law. The resulting unified model of V1 explains how orientation maps of simple and complex cells can develop, while individual neurons in the developed model express realistic orientation tuning and various surround modulation properties. In doing so, we not only offer a consistent explanation behind all these phenomena, but also create a very rich model of V1 in which the interactions between various V1 properties can be studied. The model allows us to formulate several novel predictions that relate the variation of single cell properties to their location in the orientation preference maps in V1, and we show how these predictions can be tested experimentally. Overall, this model represents a synthesis of a wide body of experimental evidence, forming a compact hypothesis for much of the development and behavior of neurons in the visual cortex.
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Kim, Taekeun Ph D. Massachusetts Institute of Technology. "Understanding experience-dependent plasticity of cellular and network activity in the mouse primary visual cortex." Thesis, Massachusetts Institute of Technology, 2019. https://hdl.handle.net/1721.1/132747.
Testo completoAbstract (sommario):
Thesis: Ph. D. in Neuroscience, Massachusetts Institute of Technology, Department of Brain and Cognitive Sciences, June, 2019<br>Cataloged from the PDF version of thesis. Vita.<br>Includes bibliographical references (pages 143-153).<br>Sensory experiences in daily life modulates corresponding primary sensory cortices and eventually alter our behavior in a befitting manner. One of the most impactful sensory modules is vision. Primary visual cortex (V1) in mammals is particularly malleable during a juvenile critical period, but this plasticity lasts even in adulthood. A representative form of visual cortical plasticity is ocular dominance (OD) plasticity following temporary monocular deprivation (MD). Here, we used a mouse model of amblyopia and revealed that juvenile OD plasticity, which manifests as depression of response to the deprived eye, requires expression of an immediate early gene, Arc. Also, the juvenile OD shift requires the activity of N-methyl-D-aspartate (NMDA) receptors in layer 4 excitatory principal neurons in V1. Another simple but powerful phenomenon of an adult form of visual cortical plasticity is stimulus-selective response potentiation (SRP). SRP is induced simply through experience to the same gratings visual stimulus over days, resulting in potentiation of visually-evoked potentials (VEPs) in layer 4 of V1. Due to the lack of studies regarding the cellular and network activity changes coincident with the induction of SRP, we have used calcium indicator expressing mice to visualize cellular activity across days of SRP training. Using two-photon calcium imaging, we found that there is indeed no significant net change in the population of active neurons during presentation of the familiar (trained) visual stimulus. Follow-up endoscopic calcium imaging revealed that rather, there is a significant reduction of somatic calcium responses selectively for the familiar visual stimulus on the test day following 5 days of SRP induction. Interestingly, the cellular calcium response to the first presentation of the familiar visual stimulus in each block was substantially similar to the response to those of a novel, yet unseen visual stimulus. However, calcium responses to the familiar visual stimulus dramatically decreased as stimulation was repeated in each presentation block within, and across days of SRP training, whereas the response to the novel visual stimulus on the test day was maintained. The findings that short-latency VEP responses are potentiated, while the slower responses revealed by calcium imaging are depressed suggest that feedback inhibition in V1 is strongly recruited by visual recognition of familiar stimulus. A number of previous studies have suggested that deficits in experience-dependent sensory cortical plasticity and perceptual learning are associated with neuropsychiatric disorders such as autism spectrum disorder (ASD), Rett syndrome and schizophrenia. Our results, therefore, may contribute to our understanding of the underlying mechanisms of these disorders and may help inform ways of intervention and treatments.<br>by Taekeun Kim.<br>Ph. D. in Neuroscience<br>Ph.D.inNeuroscience Massachusetts Institute of Technology, Department of Brain and Cognitive Sciences
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Le, Bec Benoît. "Lateral connectivity : propagation of network belief and hallucinatory-like states in the primary visual cortex." Thesis, Sorbonne université, 2018. http://www.theses.fr/2018SORUS509.
Testo completoAbstract (sommario):
Dans le cortex visuel primaire (V1), nous avons examiné l’impact fonctionnel de séquences de mouvement apparent centripète provenant de la périphérie lointaine et convergeant vers le champ récepteur de cellules corticales le long de leur axe d’orientation préféré. A haute vitesse saccadique, la congruence anisotrope de stimuli élémentaires composants un mouvement cohérent est cruciale dans la diffusion et l’intégration latérale d’information contextuelle. Au niveau électrophysiologique, ces résultats correspondent à une avance de latence et à un gain d’amplitude des réponses sous et supraliminaires, indiquant l’existence d’un champ d’association dynamique où forme et mouvement sont liés dès V1. Restreindre le mouvement apparent à la périphérie silencieuse résulte en une invasion du champ récepteur par une activité prédictive. Celle-ci suggère l'existence d'un mécanisme de diffusion latérale propre à V1 permettant de résoudre le problème d’extrapolation du mouvement. Deuxièmement, nous postulons que les hallucinations géométriques reflètent une opposition spatiale longue distance de la connectivité horizontale qui structure l'organisation de l'activité spontanée de V1, s'exprimant au travers d'un modèle d'intéractions entre hypercolonnes. Nous avons créé des stimuli visuels dans lesquels la perturbation par un bruit en 1/fα d'un réseau fortement adapté à des inducteurs géométriques induit la perception de planforms opposés. Nos résultats suggèrent que ces percepts dynamiques correspondent à la propagation de vagues d'activités détectables au niveau de cellules de V1 sous la forme d'oscillations compatibles avec la géométrie locale et la dynamique des percepts<br>In the primary visual cortex (V1), we examined the functional impact of centripetal apparent motion sequences originating from the far periphery and converging towards the receptive field of cortical cells along their preferred orientation axis. At high saccadic speed, the anisotropic congruency of elementary stimuli composing a coherent motion is crucial in the diffusion and lateral integration of contextual information. At the electrophysiological level, those results correspond to a latency advance and an amplitude gain of sub and suprathreshold responses, indicating the existence of a dynamic association field where form and motion are already bound in V1. Restricting the apparent motion to the silent periphery result in an invasion of the receptive field by predictive activity. This latter suggests the existence of a mechanism of lateral diffusion intrinsic to V1 that allows to solve the motion extrapolation problem. Second, we posit that geometric hallucinations reflect a long-distance spatial opponency of horizontal connectivity that structure the self organization of V1 ongoing activity, expressing itself through a model of interacting hypercolumns resulting in the formation of neural stripes on V1 surface. We designed visual stimuli in which perturbation by a 1/fα noise of a network highly adapted to geometric inducers result in perception of opponent planforms. Our results suggest that those dynamic percepts correspond to propagating waves of synaptic activity that are detectable at the level of V1 cells under the form of oscillations compatible with the local geometry and the dynamic of the induced percepts
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Stimberg, Marcel [Verfasser], and Klaus [Akademischer Betreuer] Obermayer. "Computational models of contrast and orientation processing in primary visual cortex / Marcel Stimberg. Betreuer: Klaus Obermayer." Berlin : Universitätsbibliothek der Technischen Universität Berlin, 2011. http://d-nb.info/1016533322/34.
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Goodyear, Bradley Gordon. "fMRI of human primary visual cortex at submillimeter resolution, ocular dominance and contrast perception in amblyopia." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape7/PQDD_0001/NQ42523.pdf.
Testo completo
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Hunt, Brendan Joel. "Synapse loss from the rhesus monkey primary visual cortex does not correlate with cognitive decline during aging." Thesis, Boston University, 2013. https://hdl.handle.net/2144/12122.
Testo completoAbstract (sommario):
Thesis (M.A.)--Boston University<br>The effect of age on synapses in the neuropil of layers 2/3 in primary visual cortex was determined in 12 rhesus monkeys of various ages (6-33 years old). All of the monkeys had been behaviorally tested. As determined using the size–frequency method, there is a decrease in the numerical density of symmetric, but not asymmetric, synapses with age. There is no significant correlation between the loss of symmetric synapse frequency and the cognitive impairment indices (CII) of the 12 behaviorally tested monkeys. This lack of correlation between synapse frequency reduction and cognitive decline presumably relates to the fact that the primary visual cortex does not have a direct role in subserving cognition.