Dissertations / Theses on the topic 'Visual oscillations'
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Beardsley, Burt Jay. "The visual shape and multipole moments of the sun." Diss., The University of Arizona, 1987. http://hdl.handle.net/10150/184229.
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This thesis describes the 1983 solar shape investigation performed at the Santa Catalina Laboratory for Experimental Relativity by Astrometry (SCLERA). Solar diameter measurements, with the North Solar Pole defined as θ = 0° polar angle, have been made between the following polar coordinates: from θ = 0° to θ = 180° (the polar diameter), from θ = 90° to θ = -90° (the equatorial diameter), from θ = -45° to θ = 135° and from θ = 45° to θ = -135°. Expressing the Sun's apparent shape in terms of a Legendre series, these diameters have enabled the calculation of the P₂ (quadrupole) and P₄ (hexadecapole) shape coefficients. The theoretical framework used to provide a relationship between the observed shape of the Sun and the multipole moments of the solar gravitational potential field has been improved to include, in general, the effect of differential rotation in both latitude and radius. Using the shape coefficients and the theoretical framework, the gravitational potential multipole moments, expressed as the P₂ and P₄ coefficients of a Legendre series, have been found to be J₂ = (3.4 ± 1.3)E-6 and J₄ = (1.7 ± 1.1)E-6, respectively. It has been found that the contribution to the perihelion precession of Mercury's orbit, caused by the combined effects from the gravitational quadrupole term and general relativity, was approximately 1σ different from the observed amount after all other known Newtonian contributions had been removed from the observed precession. The total apparent oblateness ΔR (equator-polar radii) found from SCLERA observations is ΔR = 13.8 ± 1.3 milliarcseconds. The surface rotation contribution ΔR' to the apparent solar shape is ΔR' = 7.9 milliarcseconds. The quoted uncertainties represent formal statistical 1σ errors only. Also, it has been shown that large changes in the apparent limb darkening functions were occurring near the equatorial regions of the Sun during the time of the observations. Evidence for periodic shape distortions near the equator have also been found.
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Wieczorek, Kacper. "Investigating the relationship between microsaccades and oscillations in the human visual cortex." Thesis, Cardiff University, 2015. http://orca.cf.ac.uk/86785/.
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Neural oscillations play important roles in vision and attention. Most studies of oscillations use visual fixation to control the visual input. Small eye movements, called microsaccades, occur involuntarily ~ 1-2 times per second during fixation and they are also thought to play important roles in vision and attention. The aim of the work described in this thesis was to explore the relationship between microsaccades and oscillations in the human visual cortex. In Chapter 2, I describe how remote video eye tracking can be used to detect and characterize microsaccades during MEG recordings. Tracking based on the pupil position only, without corneal reflection, and with the participant’s head immobilized in the MEG dewar, resulted in high precision gaze tracking and enabled the following investigations. In Chapter 3, I investigated the relationship between induced visual gamma oscillations and microsaccades in a simple visual stimulation paradigm. I did not find evidence for the relationship. This finding supports the view that sustained gamma oscillations reflect local processing in cortical columns. In addition, early transient gamma response had a reduced amplitude on trials with microsaccades, however the exact nature of this effect will have to be determined in future studies. In Chapter 4, I investigated the relationship between alpha oscillations and microsaccades in covert spatial attention. I did not find evidence for a relationship between hemispheric lateralization of the alpha amplitude and the directional bias of microsaccades. I propose that microsaccades and alpha oscillations represent two independent attentional mechanisms - the former related to early attention shifting and the latter to maintaining sustained attention. In Chapter 5, I recorded, for the first time, microsaccade-related spectral responses. Immediately after their onset, microsaccades increased amplitude in theta and beta bands and this effect was modulated by stimulus type. Moreover, microsaccades reduced alpha amplitude ~ 0.3 s after their onset and this effect was independent of stimulus type. These results have important implications for the interpretation of the classical oscillatory effects in the visual cortex as well as for the role of microsaccades in vision and attention.
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Adjamian, Peyman. "Magnetoencephalography: technical improvements in image co-registration and studies of visual cortical oscillations." Thesis, Aston University, 2002. http://publications.aston.ac.uk/12253/.
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The work presented in this thesis is divided into two distinct sections. In the first, the functional neuroimaging technique of Magnetoencephalography (MEG) is described and a new technique is introduced for accurate combination of MEG and MRI co-ordinate systems. In the second part of this thesis, MEG and the analysis technique of SAM are used to investigate responses of the visual system in the context of functional specialisation within the visual cortex. In chapter one, the sources of MEG signals are described, followed by a brief description of the necessary instrumentation for accurate MEG recordings. This chapter is concluded by introducing the forward and inverse problems of MEG, techniques to solve the inverse problem, and a comparison of MEG with other neuroimaging techniques. Chapter two provides an important contribution to the field of research with MEG. Firstly, it is described how MEG and MRI co-ordinate systems are combined for localisation and visualisation of activated brain regions. A previously used co-registration methods is then described, and a new technique is introduced. In a series of experiments, it is demonstrated that using fixed fiducial points provides a considerable improvement in the accuracy and reliability of co-registration. Chapter three introduces the visual system starting from the retina and ending with the higher visual rates. The functions of the magnocellular and the parvocellular pathways are described and it is shown how the parallel visual pathways remain segregated throughout the visual system. The structural and functional organisation of the visual cortex is then described. Chapter four presents strong evidence in favour of the link between conscious experience and synchronised brain activity. The spatiotemporal responses of the visual cortex are measured in response to specific gratings. It is shown that stimuli that induce visual discomfort and visual illusions share their physical properties with those that induce highly synchronised gamma frequency oscillations in the primary visual cortex.
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Gallina, Jessica <1990>. "Alpha oscillations index the functionality and the plastic changes of the visual system." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2022. http://amsdottorato.unibo.it/10265/1/Jessica_Gallina_PhD_Thesis.pdf.
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Alpha oscillations are linked to visual awareness and to the periodical sampling of visual information, suggesting that alpha rhythm reflect an index of the functionality of the posterior cortices, and hence of the visual system. Therefore, the present work described a series of studies investigating alpha oscillations as a biomarker of the functionality and the plastic modifications of the visual system in response to lesions to the visual cortices or to external stimulations. The studies presented in chapter 5 and 6 showed that posterior lesions alter alpha oscillations in hemianopic patients, with reduced alpha reactivity at the eyes opening and decreased alpha functional connectivity, especially in right-lesioned hemianopics, with concurrent dysfunctions in the theta range, suggesting a specialization of the right hemisphere in orchestrating alpha oscillations and coordinating complex interplays among different brain rhythms. The study presented in chapter 7 investigated a mechanism of rhythmical attentional sampling of visual information in healthy participants, showing that perceptual performance is influenced by a rhythmical mechanism of attentional allocation, occurring at lower-alpha frequencies (i.e., 7 Hz), when a single spatial location is monitored, and at lower frequencies (i.e., 5 Hz), when attention is allocated to two spatial locations. Moreover, the right hemisphere seemed to have a dominance in this rhythmical attentional sampling, distributing attentional resources to the entire visual field. Finally, the study presented in chapter 8 showed that prolonged visual entrainment induce long-term modulations of resting-state alpha activity in healthy participants, suggesting that persistent modifications in the functionality of the visual system are possible. Altogheter, these findings show that functional processes and plastic changes of the visual system are reflected in alpha oscillatory patterns. Therefore, investigating and promoting alpha oscillations may contribute to the development of rehabilitative protocols to ameliorate the functionality of the visual system, in brain lesioned patients.
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Myers, Nicholas. "The role of cortical oscillations in the control and protection of visual working memory." Thesis, University of Oxford, 2015. https://ora.ox.ac.uk/objects/uuid:c85253e0-6713-4fbc-801b-5f5bc8dea705.
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Visual working memory (WM) is the ability to hold information in mind for a short time before acting on it. The capacity of WM is strikingly limited. To make the most of this precious resource, humans exhibit a high degree of cognitive flexibility: We can prioritize information that is relevant to behavior, and inhibit unnecessary distractions. This thesis examines some behavioral and neural correlates of flexibility in WM. When information is of particular importance, anticipatory attention can be directed to where it will likely appear. Oscillations in visual cortex, in the 10-Hz range, play an important role in regulating excitability of such prioritized locations. Chapter 4 describes how even spontaneous fluctuations in 10-Hz synchronization (measured by electroencephalography, EEG) before encoding influence WM. Chapters 2 and 3 describe how attention can be directed retrospectively to items even if they are already stored in WM. Chapter 3 discusses how retrospective cues change neural synchronization similarly to anticipatory cues. Behavioral and neural measures additionally indicate that the boosting of an item through retrospective cues does not require prolonged deployment of attention: rather, it may be a transient process. The second half of this thesis additionally examines how items are represented in visual WM. Chapter 5 summarizes a study using pattern analysis of magnetoencephalographic (MEG) and EEG data to decode features of visual templates stored in WM. Decoding appears transiently around the time when potential target stimuli are expected, in line with a flexible reactivation mechanism. Chapter 6 further examines separate cortical networks involved in protecting vs. updating items in WM, and tests whether task relevance changes how well WM contents can be decoded. Finally, Chapter 7 summarizes the thesis and discusses how attentional flexibility can merge WM with a wider range of sources of behavioral control.
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Lowe, Scott Corren. "Decoding information from neural populations in the visual cortex." Thesis, University of Edinburgh, 2017. http://hdl.handle.net/1842/28861.
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Visual perception in mammals is made possible by the visual system and the visual cortex. However, precisely how visual information is coded in the brain and how training can improve this encoding is unclear. The ability to see and process visual information is not an innate property of the visual cortex. Instead, it is learnt from exposure to visual stimuli. We first considered how visual perception is learnt, by studying the perceptual learning of contrast discrimination in macaques. We investigated how changes in population activity in the visual cortices V1 and V4 correlate with the changes in behavioural response during training on this task. Our results indicate that changes in the learnt neural and behavioural responses are directed toward optimising the performance on the training task, rather than a general improvement in perception of the presented stimulus type. We report that the most informative signal about the contrast of the stimulus within V1 and V4 is the transient stimulus-onset response in V1, 50 ms after the stimulus presentation begins. However, this signal does not become more informative with training, suggesting it is an innate and untrainable property of the system, on these timescales at least. Using a linear decoder to classify the stimulus based on the population activity, we find that information in the V4 population is closely related to the information available to the higher cortical regions involved with decision making, since the performance of the decoder is similar to the performance of the animal throughout training. These findings suggest that training the subject on this task directs V4 to improve its read out of contrast information contained in V1, and cortical regions responsible for decision making use this to improve the performance with training. The structure of noise correlations between the recorded neurons changes with training, but this does not appear to cause the increase in behavioural performance. Furthermore, our results suggest there is feedback of information about the stimulus into the visual cortex after 300 ms of stimulus presentation, which may be related to the high-level percept of the stimulus within the brain. After training on the task, but not before, information about the stimulus persists in the activity of both V1 and V4 at least 400 ms after the stimulus is removed. In the second part, we explore how information is distributed across the anatomical layers of the visual cortex. Cortical oscillations in the local field potential (LFP) and current source density (CSD) within V1, driven by population-level activity, are known to contain information about visual stimulation. However the purpose of these oscillations, the sites where they originate, and what properties of the stimulus is encoded within them is still unknown. By recording the LFP at multiple recording sites along the cortical depth of macaque V1 during presentation of a natural movie stimulus, we investigated the structure of visual information encoded in cortical oscillations. We found that despite a homogeneous distribution of the power of oscillations across the cortical depth, information was compartmentalised into the oscillations of the 4 Hz to 16 Hz range at the granular (G, layer 4) depths and the 60Hz to 170Hz range at the supragranular (SG, layers 1–3) depths, the latter of which is redundant with the population-level firing rate. These two frequency ranges contain independent information about the stimulus, which we identify as related to two spatiotemporal aspects of the visual stimulus. Oscillations in the visual cortex with frequencies < 40 Hz contain information about fast changes in low spatial frequency. Frequencies > 40 Hz and multi-unit firing rates contain information about properties of the stimulus related to changes, both slow and fast, at finer-grained spatial scales. The spatiotemporal domains encoded in each are complementary. In particular, both the power and phase of oscillations in the 7 Hz to 20Hz range contain information about scene transitions in the presented movie stimulus. Such changes in the stimulus are similar to saccades in natural behaviour, and this may be indicative of predictive coding within the cortex.
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Moratti, Stephan. "Modulation of stimulus driven neuronal oscillations by the emotional and motivational significance of visual stimuli." [S.l.] : [s.n.], 2005. http://deposit.ddb.de/cgi-bin/dokserv?idn=975676911.
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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.
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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 perceptsIn 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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ZAZIO, AGNESE. "Impact of ongoing alpha oscillations on visual perception and neurophysiological response: an integration with a psychophysical approach." Doctoral thesis, Università degli Studi di Milano-Bicocca, 2019. http://hdl.handle.net/10281/241241.
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Le oscillazioni neurali sono considerate elementi costitutivi del funzionamento cognitivo, e negli ultimi decenni i neuroscienziati hanno sviluppato teorie fondamentali sul ruolo delle oscillazioni nelle dinamiche cerebrali. Recentemente, un crescente numero di evidenze ha mostrato come l’attività oscillatoria in corso possa rendere conto di una porzione considerevole della variabilità che si osserva nella prestazione comportamentale e nella risposta neurofisiologica. Nel dominio della percezione visiva, un ruolo cruciale è svolto dalle oscillazioni neurali nel range di frequenza alfa. Si ritiene che l’attività alfa eserciti una funzione inibitoria sull’elaborazione dello stimolo e rifletta l’eccitabilità corticale. E’ stato recentemente proposto che il ritmo alfa non possa essere considerato come un fenomeno unitario; tuttavia, si conosce ancora poco riguardo ai meccanismi neurali associati con l’attività alfa misurata attraverso registrazioni non invasive. Inoltre, fino ad ora la maggior parte degli studi sugli effetti dell’attività in corso sulla percezione visiva si è focalizzata su una particolare classe di stimoli, ovvero che hanno un’intensità vicino alla soglia sensoriale, e si conosce molto meno riguardo a cosa avvenga in risposta a stimoli la cui intensità va oltre il valore di soglia.
Nel presente lavoro, ci siamo posti l’obiettivo di affrontare tali questioni studiando gli effetti dell’attività alfa in corso sulla risposta percettiva e neurofisiologica nel dominio visivo. Il primo obiettivo era quello di replicare alcune evidenze sugli effetti del power e della fase delle fluttuazioni spontanee dell’attività alfa pre-stimolo sulla detezione visiva, utilizzando stimoli a soglia. In aggiunta allo studio originale, l’utilizzo della magnetoencefalografia ci ha permesso di ricostruire le sorgenti cerebrali dell’attività oscillatoria pre-stimolo e dell’attività evocata. Un secondo studio era volto a modulare l’attività alfa in corso utilizzando un paradigma di deprivazione sensoriale, e testare gli effetti di tale modulazione attraverso un ampio range di intensità di stimolazione. L’uso della stimolazione magnetica transcranica (TMS) con simultanea registrazione elettroencefalografica ci ha permesso di valutare la risposta neurofisiologica e percettiva alla TMS, attraverso i potenziali evocati e la percezione dei fosfeni. Infine, in un terzo studio abbiamo sviluppato un modello formale sugli effetti dell’attività alfa in corso sulla percezione visiva, con l’obiettivo di distinguere possibili meccanismi neurali che non possono essere disambiguati a livello non-invasivo. Il modello è basato sulle interazioni cross-frequency tra l’inibizione funzionale di alfa e l’attività gamma dei neuroni sensoriali, e mette in evidenza i vantaggi di presentare un ampio range di intensità di stimoli nello studio degli effetti dell’attività oscillatoria, utilizzando un approccio psicofisico.
Considerati insieme, i nostri risultati sono coerenti con la letteratura corrente riguardo alla funzione inibitoria svolta dall’attività alfa in corso sulla percezione visiva. Infatti, la risposta sia percettiva che neurofisiologica ad uno stimolo esterno era influenzata dall’attività alfa pre-stimolo, nelle fluttuazioni spontanee così come quando era modulata da un paradigma di deprivazione sensoriale. Inoltre, le presenti evidenze supportano l’ipotesi che le oscillazioni alfa sottendano meccanismi distinti, e mettono in luce come nuove intuizioni possano emergere dall’utilizzo di un approccio psicofisico allo studio dell’attività oscillatoria in corso sulla percezione.
Utilizzando diversi approcci metodologici, il presente lavoro fornisce nuovi avanzamenti nello studio non-invasivo delle oscillazioni sul comportamento, nello specifico sull’inibizione dell’attività alfa sulla percezione visiva.Neural oscillations are considered to be the building blocks of cognitive functioning, and in the last decades neuroscientists have developed fundamental theories on their role in brain dynamics. Recently, a growing body of evidences has shown that ongoing oscillatory activity can account for a considerable amount of variability in behavioral performance and in neurophysiological response. In the domain of visual perception, a crucial role is played by neural oscillations within alpha frequency range. Alpha activity is believed to exert an inhibitory function on stimulus processing and to reflect cortical excitability, both when it fluctuates spontaneously as well as when it is modulated, by top-down or bottom-up mechanisms. It has been recently suggested that alpha rhythm may not be considered as a unitary phenomenon; however, still little is known about the neural mechanisms associated with alpha activity as measured by non-invasive recordings. Furthermore, up to now most of the studies on the effects of ongoing alpha activity on visual perception focused on a special class of stimuli, i.e., with a near-threshold intensity, and much less is known about what happens in the response beyond sensory threshold. In the present work, we aimed at addressing these issues by studying the effects of ongoing alpha oscillations on perceptual and neurophysiological outcome in the visual domain. The first goal was to replicate recent findings on the effects of spontaneous fluctuations of pre-stimulus alpha power and phase on a visual detection task, by using near-threshold stimuli. In addition to the original study, the use of magnetoencephalography allowed us to reconstruct brain sources of pre-stimulus and evoked activity. In a second study, we aimed at modulating ongoing alpha activity by using a sensory deprivation paradigm, and tested the effects of such modulation by means of a wide range of stimulation intensities. The use of transcranial magnetic stimulation (TMS) with concurrent electroencephalography allowed to directly assess the neurophysiological and perceptual response to TMS, by means of TMS-evoked potentials and phosphene perception. Finally, in a third study we developed a formal model of the effects of ongoing alpha activity on visual perception, with the aim of disentangling possible neural mechanisms which cannot be discerned non-invasively. The model is based on cross-frequency interactions between alpha functional inhibition and gamma activity of sensory neurons and highlights the advantages of presenting a wide range of stimulus intensities in the study of the effects of pre-stimulus oscillatory activity, using a psychophysical approach. Taken together, our results are consistent with current literature about the inhibitory function played by ongoing alpha activity on visual perception. Indeed, both perceptual and neurophysiological response to an external stimulus were affected by pre-stimulus alpha activity, when it fluctuated spontaneously as well as when it was modulated by a sensory deprivation paradigm. Moreover, the present findings support the hypothesis that alpha oscillations subtend distinct mechanisms, and highlighted that new insights may arise from applying a psychophysical approach to the study of ongoing activity on perception. By using different methodological approaches, the present work provides novel advances in the field of non-invasive investigation of ongoing oscillations on behavior, specifically on alpha inhibition of visual perception.
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Barnes, William Halley [Verfasser], Ralf A. W. [Akademischer Betreuer] Galuske, and Matthias H. J. [Akademischer Betreuer] Munk. "Reversible Visual Hemineglect: the Role of Neural Oscillations in Primary Visual Cortex / William Barnes. Betreuer: Ralf A. W. Galuske ; Matthias H. J. Munk." Darmstadt : Universitäts- und Landesbibliothek Darmstadt, 2016. http://nbn-resolving.de/urn:nbn:de:tuda-tuprints-51931.
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Barnes, William [Verfasser], Ralf A. W. [Akademischer Betreuer] Galuske, and Matthias H. J. [Akademischer Betreuer] Munk. "Reversible Visual Hemineglect: the Role of Neural Oscillations in Primary Visual Cortex / William Barnes. Betreuer: Ralf A. W. Galuske ; Matthias H. J. Munk." Darmstadt : Universitäts- und Landesbibliothek Darmstadt, 2016. http://d-nb.info/111204468X/34.
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Fiorini, Matilde [Verfasser]. "NMDARs hypofunction in parvalbumin-expressing interneurons alters oscillations and sensory tuning in mouse primary visual cortex / Matilde Fiorini." Tübingen : Universitätsbibliothek Tübingen, 2020. http://d-nb.info/1219903434/34.
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Brüers, Sasskia. "Towards a « Neuro-Encryption » system : from understanding the influence of brain oscillations in vision to controlling perception." Thesis, Toulouse 3, 2017. http://www.theses.fr/2017TOU30195/document.
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L'activité de notre cerveau est intrinsèquement rythmique : des oscillations sont observées à tous les niveaux de son organisation. Cette rythmicité de l'activité cérébrale influence notre perception. En effet, au lieu de superviser continuellement notre environnement, notre cerveau effectue de brèves " clichés " du monde extérieur (entre 5 et 15 par seconde). Cela crée des cycles perpétuels : notre perception visuelle fluctue en fonction de la phase de l'oscillation sous- jacente. De nombreuses données témoignent du fait que les oscillations cérébrales à différentes fréquences sont fondamentales à la formation de notre perception visuelle. Lors de cette thèse, nous avons utilisé le Paradigme de Bruit Blanc comme outil pour comprendre l'influence des oscillations sur la perception visuelle et qui par extension pourra être utilisé pour contrôler cette perception. Le paradigme de bruit blanc visuel utilise des séquences de flashs dont la luminance varie aléatoirement (créant ainsi du " bruit blanc "), comme stimuli, qui contraignent l'activité cérébrale de manière prédictible. Les réponses impulsionnelles à ces séquences de bruit blanc sont caractérisées par une composante oscillatoire forte dans la bande alpha (~10Hz), similaire à un écho perceptuel. Puisque les réponses impulsionnelles sont un modèle de la réponse de notre cerveau à un flash dans la séquence de bruit blanc, elles peuvent être utilisées pour reconstruire (plutôt qu'enregistrer) l'activité cérébrale en réponse à de nouvelles séquences de stimulation. Par ailleurs, des cibles ont été introduites au sein des séquences de bruit blanc à un niveau proche du seuil de perception, et le décours temporel de cette activité reconstruite autour de la présentation des cibles a été extrait. Ainsi, l'EEG reconstruit peut être utilisé pour étudier l'influence de ces oscillations contraintes sur la perception visuelle, indépendamment des autres types de signaux généralement enregistrés dans l'EEG. Dans un premier temps, nous avons validé le paradigme de bruit blanc en montrant que : 1) les séquences de bruits blancs influencent bien la détection des cibles, 2) les échos perceptuels évoqués par les séquences de bruit blancs sont stables dans le temps, 3) ces échos sont un bon modèle de l'activité cérébrale enregistrée par EEG, et 4) leurs bases neuronales se situent dans les aires visuelles primaires. Dans un second temps, nous avons étudié la relation entre ces oscillations cérébrales contrôlées par la séquence de bruit blanc et la détection des cibles. Ici, nous montrons que l'activité EEG reconstruite nous aide à déterminer la véritable latence à laquelle la phase de l'oscillation (thêta) influence la perception. De plus, nous avons aussi montré que l'amplitude de l'oscillation (alpha) influence la détection des cibles et ce, indépendamment des fluctuations des facteurs endogènes (tel que l'attention). Enfin, tirant parti de ce lien entre oscillation et perception, nous construisons deux algorithmes qui permettent de contrôler la perception des sujets. Tout d'abord, nous mettons au point un modèle " universel " de la perception qui permet de prédire, pour n'importe quel observateur, si une cible dans une séquence de bruit blanc sera vue ou non. Ensuite, nous construisons un modèle individuel qui utilise l'écho perceptuel de chaque sujet comme clé de cryptage et nous permet de présenter des cibles à des moments où la cible sera détectée par un sujet seulement au détriment de tous les autres sujets, créant ainsi une sorte de système de cryptage neuronal (" Neuro-Encryption ")Our brain activity is inherently rhythmic: oscillations can be found at all levels of organization. This rhythmicity in brain activity gives a rhythm to what we see: instead of continuously monitoring the environment, our brains take "snapshots" of the external world from 5 to 15 times a second. This creates perceptual cycles: depending on the phase of the underlying oscillation, our perceptual abilities fluctuate. Accumulating evidence shows that brains oscillations at various frequencies are instrumental in shaping visual perception. At the heart of this thesis lies the White Noise Paradigm, which we designed as a tool to better understand the influence of oscillations on visual perception and which ultimately could be used to control visual perception. The White Noise Paradigm uses streams of flashes with random luminance (i.e. white noise) as stimuli, which have been shown to constrain brain oscillations in a predictable manner. The impulse response to WN sequences has a strong (subject specific) oscillatory component at ~10Hz akin to a perceptual echo. Since the impulse response is a model of how our brains respond to one single flash in the sequence, they can be used to reconstruct (rather than record) the brain activity to new stimulation sequences. We then present near-perceptual threshold targets embedded within the WN sequences and extract the time course of these predicted/reconstructed background oscillations around target presentation. Thus, the reconstructed EEG can be used to study the influence of the oscillatory components on visual perception, independently of other types of signals usually recorded in the EEG. First, we validate the White Noise Paradigm by showing that: 1) the WN sequences do modulate behaviour, 2) the perceptual echoes evoked by these WN sequences are stable in time, 3) they are a (relatively) good model of the subject's recorded brain activity and 4) their neuronal basis can be found in the early visual areas. Second, we investigate the relationship between these constrained brain oscillations and visual perception. Specifically, we show that the reconstructed EEG can help us recover the true latency at which (theta) phase influences perception. Moreover, it can help us uncover a causal influence of (alpha) power on target detection, independently from any fluctuation in endogenous factors. Finally, capitalizing on the link between oscillations and perception, we build two algorithms used to control the perception of subjects. First, we build a "universal" forward model which can predict for any observer whether a particular target will be seen or not. Second, we build a subject-dependent model which can predict whether a particular subject (for whom EEG was recorded previously) will perceive a given target or not. Critically, this can be used to present targets optimized to be perceived by one subject only, to the detriment of all other subjects, creating a sort of "Neuro-Encryption" system
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Chanes, Puiggros Lorena. "Frontal and parietal contributions to visual perception in humans." Phd thesis, Université Pierre et Marie Curie - Paris VI, 2014. http://tel.archives-ouvertes.fr/tel-00989767.
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Frontal and parietal areas have been shown to subtend different cognitive processes such as attentional orienting, decision making and access to consciousness, with bearing on visual performance. In spite of prior evidence supporting an implication of those regions in visual cognition, their contributions to the processing of low-contrast unmasked stimuli and the characteristic spatiotemporal activity patterns underlying them remain to be fully explored and causation is lacking. We here addressed a thorough exploration of such contributions in humans, with an emphasis on the dynamics of neural activity and visual performance enhancements as probed by patterns of noninvasive manipulation of local brain oscillatory activity. To this end, we tested in healthy participants the effects of either single pulses or short bursts of active vs. sham transcranial magnetic stimulation (TMS), delivered to the frontal eye field (FEF) and the intraparietal sulcus (IPS) prior to the presentation of a lateralized low-contrast near-threshold Gabor stimulus, on the visual discrimination and conscious detection of such stimulus. Our findings contribute to better substantiate the oscillatory basis of visual cognition and its associated behaviors and to set the stage for the development of novel therapies based on noninvasive manipulation of dysfunctional brain oscillatory activity.
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Notbohm, Annika [Verfasser], Christoph S. [Akademischer Betreuer] Herrmann, and Jonas [Akademischer Betreuer] Obleser. "The role of Steady- State Visual Evoked Potentials in the study of brain oscillations / Annika Notbohm ; Christoph Siegfried Herrmann, Jonas Obleser." Oldenburg : BIS der Universität Oldenburg, 2017. http://nbn-resolving.de/urn:nbn:de:gbv:715-oops-30990.
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Notbohm, Annika [Verfasser], Christoph Siegfried [Akademischer Betreuer] Herrmann, and Jonas [Akademischer Betreuer] Obleser. "The role of Steady- State Visual Evoked Potentials in the study of brain oscillations / Annika Notbohm ; Christoph Siegfried Herrmann, Jonas Obleser." Oldenburg : BIS der Universität Oldenburg, 2017. http://d-nb.info/1127208616/34.
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Luo, Canhuang. "Le rôle des oscillations du cerveau dans la perception visuelle, l'attention et la conscience." Thesis, Toulouse 3, 2020. http://www.theses.fr/2020TOU30280.
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Les oscillations sont omniprésentes dans le cerveau. Une grande partie de la littérature soutient que les oscillations cérébrales ne sont pas un sous-produit des activités du cerveau ; en fait, elles façonnent notre perception en modulant l'excitabilité corticale et en facilitant les communications neuronales. Par conséquent, notre perception visuelle, notre attention et peut-être même notre conscience s'accroissent et diminuent au fil du temps. Cependant, le rôle des oscillations dans ces fonctions perceptives ou cognitives n'est pas entièrement compris. Pour la perception visuelle et l'attention, bien que la relation entre ces fonctions et les oscillations cérébrales ait été établie, on ne sait pas exactement où et comment ces oscillations cérébrales sont générées. En ce qui concerne la conscience, on ignore encore comment les oscillations sont impliquées dans la production de la perception consciente. Ce sont les questions que la présente thèse tente d'aborder. La thèse commence par des oscillations cérébrales dans la fonction cérébrale la plus élémentaire et la mieux comprise - la perception visuelle. Il a été suggéré que la perception visuelle est un processus oscillatoire, échantillonnant le monde à la fréquence alpha. Les échos perceptifs sont une démonstration de l'échantillonnage visuel. L'écho est une fonction de réponse impulsionnelle qui oscille à ~10 Hz en réponse à des stimuli de bruit blanc. Alors que les propriétés temporelles sont progressivement révélées, l'origine des échos reste floue. La première étude s'est attachée à étudier la base neurale des échos perceptifs, et nous avons découvert que les échos proviennent du cortex visuel primitif. Ensuite, nous passons à l'attention. Il a été démontré que l'attention échantillonne l'environnement à la fréquence thêta. Une étude sur les singes suggère que l'oscillation thêta de l'attention peut provenir des interactions compétitives du champ réceptif de V4. Pour savoir si ce mécanisme peut être généralisé aux humains, nous reproduisons l'expérience comportementale chez les humains. Enfin, dans les deux dernières études, nous examinons les oscillations du cerveau dans la conscience. En utilisant la rivalité binoculaire, nous cherchons d'abord à savoir si les échos perceptifs nécessitent une conscience. Les résultats montrent que les échos perceptifs peuvent être déclenchés à la fois lorsque le stimulus est dans la conscience et en dehors de la conscience. Ensuite, nous étudions le flux d'informations pendant la rivalité binoculaire et montrons une augmentation des activités bêta et thêta de haut en bas avant les commutations perceptuelles. En conclusion, le cerveau est un système dynamique dans lequel les oscillations facilitent de manière flexible diverses fonctions cérébrales en jouant différents rôles fonctionnelsOscillations are ubiquitous in the brain. A large body of literature has supported that brain oscillations are not a by-product of brain activities; in fact, they shape our perception by modulating cortical excitability and facilitating neuronal communications. Consequently, our visual perception, attention and maybe even consciousness wax and wane across time. However, the role of oscillations in these perceptual or cognitive functions is not entirely understood. For visual perception and attention, although the relationship between them and brain oscillations has been established, it is unclear where and how these brain oscillations are generated. As for consciousness, how the oscillations are involved in producing conscious perception remains unknown. These are the questions the current thesis attempts to address. The thesis starts with brain oscillations in the most basic and best understood brain function - visual perception. It has been suggested that visual perception is an oscillatory process, sampling the world at the alpha frequency. Perceptual echoes are one demonstration of visual sampling. The echo is an impulse response function that oscillates at ~10 Hz in response to white-noise stimuli. While the temporal properties are gradually revealed, the origin of the echoes remains unclear. The first study set out to study the neural basis of perceptual echoes, and we found the echoes originate in the early visual cortex. Next, we move on to attention. It has been shown that attention samples the environment at theta frequency. A monkey study suggests that the theta oscillation of attention may arise from competitive receptive field interactions of V4. To investigate if the mechanism can be generalized to humans, we replicate the behavioral experiment in humans. Finally, in the last two studies, we examine brain oscillations in consciousness. Utilizing binocular rivalry, we first investigate if the perceptual echoes require consciousness. The results show that perceptual echoes can be elicited both when the stimulus is in consciousness and out of consciousness. Second, we investigate information flow during binocular rivalry and show an increased top-down beta and theta activities before perceptual switches. In conclusion, the brain is a dynamic system in which the oscillations flexibly facilitate various brain functions by playing different functional roles
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Cevallos, Barragan Carlos. "THE RESONANCE OF BIOLOGICAL MOTION THROUGH VISUAL PERCEPTION IN THE HUMAN BRAIN." Doctoral thesis, Universite Libre de Bruxelles, 2016. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/235472.
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Taking research as a tool to learn how new technology can develop new diagnosis and treatment methods in the physical field, takes place the education in motor sciences. On one hand, current research has shed light into novel methods to improve motor performance for athletes as well as for people learning new motor gestures. On the other hand it has also helped to improve treatment efficiency for people suffering motor cerebral lesions like: cerebrovascular attack (CVA) and cerebral palsy. This doctoral thesis addresses different protocols to analyze motor gestures and brain oscillations through visual perception.Our brain encompasses a changing symphony of oscillating activity throughout our lives. Up to the time we are born, we are ready to feel and move to interact with our world. Our senses develop rapidly and we start to perceive the world and learn. We visually perceive and process big amounts of information on a daily basis. At the same time we see movements from ourselves and from others in order to communicate and interact with our environment. We watch the world move. Moreover, from the links that exist between motor and sensory systems in human beings we may approach individual motor activity as a loop between a control (brain) over the effectors (muscles) which act, perceive and send the information back to the control source.The present group of works presented in this doctoral thesis is based on the correlation between human brain scalp activity, measured by means of electroencephalography (EEG) recordings, visual perception and its interpretation through different approaches.Doctorat en Sciences de la motricité
info:eu-repo/semantics/nonPublished
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Freitag, F?bio Batista. "Encoding mechanisms based on fast oscillations in the retina of the cat and their dependencies on anesthesia." Universidade Federal do Rio Grande do Norte, 2013. http://repositorio.ufrn.br:8080/jspui/handle/123456789/17028.
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Processing in the visual system starts in the retina. Its complex network of cells with different properties enables for parallel encoding and transmission of visual information to the lateral geniculate nucleus (LGN) and to the cortex. In the retina, it has been shown that responses are often accompanied by fast synchronous oscillations (30 - 90 Hz) in a stimulus-dependent manner. Studies in the frog, rabbit, cat and monkey, have shown strong oscillatory responses to large stimuli which probably encode global stimulus properties, such as size and continuity (Neuenschwander and Singer, 1996; Ishikane et al., 2005). Moreover, simultaneous recordings from different levels in the visual system have demonstrated that the oscillatory patterning of retinal ganglion cell responses are transmitted to the cortex via the LGN (Castelo-Branco et al., 1998). Overall these results suggest that feedforward synchronous oscillations contribute to visual encoding. In the present study on the LGN of the anesthetized cat, we further investigate the role of retinal oscillations in visual processing by applying complex stimuli, such as natural visual scenes, light spots of varying size and contrast, and flickering checkerboards. This is a necessary step for understanding encoding mechanisms in more naturalistic conditions, as currently most data on retinal oscillations have been limited to simple, flashed and stationary stimuli. Correlation analysis of spiking responses confirmed previous results showing that oscillatory responses in the retina (observed here from the LGN responses) largely depend on the size and stationarity of the stimulus. For natural scenes (gray-level and binary movies) oscillations appeared only for brief moments probably when receptive fields were dominated by large continuous, flat-contrast surfaces. Moreover, oscillatory responses to a circle stimulus could be broken with an annular mask indicating that synchronization arises from relatively local interactions among populations of activated cells in the retina. A surprising finding in this study was that retinal oscillations are highly dependent on halothane anesthesia levels. In the absence of halothane, oscillatory activity vanished independent of the characteristics of the stimuli. The same results were obtained for isoflurane, which has similar pharmacological properties. These new and unexpected findings question whether feedfoward oscillations in the early visual system are simply due to an imbalance between excitation and inhibition in the retinal networks generated by the halogenated anesthetics. Further studies in awake behaving animals are necessary to extend these conclusions
O processamento da informa??o visual se inicia na retina. A sua complexa rede de c?lulas com diferentes propriedades permite que a informa??o visual seja codificada em canais paralelos e transmitida para o n?cleo geniculado lateral (LGN) e o c?rtex. Na retina, tais respostas est?o frequentemente acompanhadas por oscila??es sincronizadas de alta frequ?ncia (30 90 Hz) em uma maneira dependente do est?mulo. Como demonstrado em estudos na r?, coelho, gato e macaco, respostas oscilat?rias ocorrem em geral a est?mulos relativamente grandes, podendo codificar propriedades globais do est?mulo como o tamanho e continuidade (Neuenschwander and Singer, 1996; Ishikane et al., 2005). Al?m disso, registros simult?neos em diferentes n?veis do sistema visual t?m mostrado que o padr?o de oscila??o nas c?lulas ganglionares retinianas ? transmitido para o c?rtex visual via LGN (Castelo-Branco et al., 1998). De uma forma geral, esses resultados sugerem que oscila??es sincronizadas em uma maneira feedforward s?o importantes na codifica??o da informa??o visual. No presente estudo feito no LGN de gatos anestesiados, investigamos o papel das oscila??es retinianas no processamento de informa??o visual atrav?s da apresenta??o de est?mulos complexos, como cenas naturais, pixels aleat?rios no tempo e espa?o, al?m de grades em movimento. Esse ? um importante passo para o entendimento de mecanismos de codifica??o em condi??es naturais, j? que grande parte dos estudos que investigaram o papel de oscila??es retinianas utilizaram-se de est?mulos simples e estacion?rios. An?lises de correla??o de respostas neuronais (spiking responses) confirmaram resultados pr?vios mostrando que respostas oscilat?rias na retina (observadas aqui a partir de registros no LGN) dependem do tamanho e estacionariedade do est?mulo. Para filmes de cenas naturais (em escala de cinza e preto e branco) oscila??es apareceram apenas por breves momentos provavelmente quando os campos receptores foram dominados por padr?es extensos e cont?nuos (para ambas as escalas). As atividades oscilat?rias parecem ser dependentes de uma massa cr?tica de c?lulas ativadas sugerindo que esse padr?o regular de atividade surge atrav?s de intera??es horizontais na retina. Nossos resultados mostram, al?m disto, que surpreendentemente oscila??es da retina no gato s?o dependentes da anestesia mediada por halotano. Na aus?ncia deste, atividades oscilat?rias estiveram ausentes independentemente das caracter?sticas dos est?mulos visuais. Resultados semelhantes foram obtidos para o isoflurano, anest?sico com propriedades farmacol?gicas similares. Esse novo e inesperado resultado nos faz questionar se oscila??es feedforward no sistema visual n?o seriam resultado de um desequil?brio entre correntes de excita??o e inibi??o nas redes retinianas gerado pelos anest?sicos halogenados. Experimentos futuros em animais acordados ser?o necess?rios para confirmar essas conclus?es
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Brealy, Jennifer. "The relationship between variation in genes, GABA, structure and gamma oscillations in the visual and auditory system of healthy individuals and psychiatric disorder." Thesis, Cardiff University, 2015. http://orca.cf.ac.uk/75463/.
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Visual perception is highly variable across healthy individuals and increasing evidence suggests that this inter-individual variation could be due to differences at the genetic, neurochemical, structural and neurophysiological level. Specifically, variation in the GAD1 gene (responsible for synthesising the majority of cortical GABA) has been associated with differences in the level of the inhibitory neurotransmitter GABA. In addition, differences in GABA and cortical structural parameters (surface area and thickness) have been shown to predict differences in neural gamma oscillations. However, these findings have not been replicated in large independent studies. Hence, Chapter 3 and 4 of this thesis combines the non-invasive neuroimaging tools MRI, MRS and MEG with genetic data to investigate the relationship between variations in genes, GABA, structure and gamma oscillations in the visual cortex of a large cohort of healthy individuals. Group differences in GABA, structure and gamma oscillations have also been reported between psychiatric populations (schizophrenia and bipolar disorder) and healthy individuals. However, differences in the direction of effect (increase or decrease) and no group differences have been found. Thus, Chapter 5 aims to further study these inconsistent findings by exploring group differences in GABA, structure and gamma oscillations between a healthy group and a schizoaffective bipolar disorder group. Lastly, inter- individual variation is also present in auditory perception but has received much less attention into the factors driving this variation. As in the visual system, similar links between neurochemical, structural and neurophysiological measures could be present in the auditory domain. Chapter 6 investigates the association between auditory gamma oscillations and auditory structural parameters in a healthy cohort.
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Stengel, Chloé. "Frontal contributions to conscious visual perception through causal manipulation of brain rhythms." Thesis, Sorbonne université, 2019. http://www.theses.fr/2019SORUS354.
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Les oscillations corticales sous-tendent une grande variété de fonctions cognitives. Notamment, un rôle causal des oscillations beta-hautes dans le champ oculomoteur frontal (en anglais : FEF) droit pour l’orientation de l’attention et la facilitation de la perception a été solidement démontré. Cependant, pour la même région dans l’hémisphère gauche, il a été récemment suggéré que le bruit neuronal (càd une activité neuronale non prédictible), et non les oscillations, pourrait améliorer le traitement des stimuli sensoriels faibles et leur perception. Nous utilisons la Stimulation Magnétique Transcranienne (SMT) pour entrainer des oscillations à 30 Hz ou bien moduler le niveau de bruit neuronal dans les FEF droit et gauche et nous enregistrons les signaux EEG de sujets sains réalisant une tâche de détection consciente. Dans l’hémisphère droit, nous montrons que des rafales rythmiques de SMT accroissent la synchronisation locale et inter-régionale des oscillations beta-hautes et apportons des preuves d’un rôle causal ces oscillations dans la perception visuelle. Dans l’hémisphère gauche, nous montrons que des rafales arythmiques de SMT augmentent le niveau de bruit neuronal dans la totalité du réseau de l’attention. Enfin, nous montrons que ces effets sont causés par la stimulation corticale directe et non par la stimulation auditive associée à la décharge d’impulsions de SMT. Nous reportons seulement des effets non-spécifiques de la stimulation auditive sur la prise de décision perceptuelle ou l’activité dans le cortex auditif. Ces résultats contribuent à une meilleure compréhension des stratégies de codage neuronal dans le réseau bilatéral de l’orientation de l’attentionCortical oscillatory activity has been shown to subtend a wide variety of cognitive processes. In particular, there is strong evidence for a causal role of high-beta (30 Hz) oscillations in the right Frontal Eye Field (FEF) for the orientation of attention and the facilitation of perception. However, for the same area in the left hemisphere, recent evidence has suggested that another pattern of brain activity: neuronal noise, i.e. unpredictable neuronal activity, could enhance processing of weak sensory stimuli and be needed to improve conscious detection. We use Transcranial Magnetic Stimulation (TMS) to either entrain high-beta cortical oscillations or modulate neuronal noise level in the left and right FEFs and we record electrophysiological signals of healthy subjects performing a visual detection at threshold task.We show, in the right hemisphere, that rhythmic patterns of TMS increase high-beta local and inter-regional synchronization in fronto-parietal regions and bring strong evidence for a causal role of high-beta oscillations for conscious visual perception. In the left hemisphere, we show that arrhythmic or irregular patterns of TMS increase neuronal noise throughout the attention network. Lastly, we show that these effects are caused by direct cortical stimulation and cannot be generated by the clicking sounds associated with the discharge of TMS pulses. We report only non-specific effects of the auditory stimulation on perceptual decision-making and activity in the auditory cortex. These findings contribute to a better understanding of coding strategies in the bilateral network for attention orienting and the specific and non-specific effects of TMS
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Alexander, Kevin Eugene. "Visual Sampling with the EEG Alpha Oscillation." Wright State University / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=wright1596757044725515.
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BRINGUIER, VINCENT. "Oscillations et integration neuronale dans le cortex visuel primaire." Paris 6, 1995. http://www.theses.fr/1995PA066274.
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Les mecanismes neuronaux pouvant etre impliques dans le liage fonctionnel de l'activite corticale visuelle ont ete etudies par le moyen d'enregistrements intracellulaires du cortex visuel du chat anesthesie. Un tiers des cellules enregistrees presentent une activite oscillante en reponse a la stimulation visuelle, et cette periodicite est d'origine synaptique. La plupart des cellules presentent un champ d'integration sous-liminaire plus etendu que le champ minimum de decharge, dont l'effet sur l'activit e de la cellule depend de son niveau de depolarisation et de l'histoire recente de celui-ci
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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.
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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.
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Butler, Colleen Ann. "Motion sickness with fore-and-aft and pitch oscillation : effect of the visual scene." Thesis, University of Southampton, 2008. https://eprints.soton.ac.uk/51306/.
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Braking and acceleration expose car passengers to complex fore-and-aft and pitch motions that can cause carsickness, with the effect depending on the visual scene. Previous studies in various motion environments have suggested that external viewing reduces motion sickness relative to internal viewing or wearing a blindfold however the influences of motion and vision on motion sickness are thought to be interactive. The types of motion for which a visual scene can and cannot modify sickness are yet to be established. The aim of this research was to advance understanding of the effect of the visual scene on motion sickness caused by fore-and-aft oscillation, combinations of fore-and-aft and pitch oscillation, and pitch oscillations. The first experiment investigated the effect of the visual scene on motion sickness caused by low frequency low magnitude fore-and-aft oscillation. Six groups of 20 subjects experienced one of six visual scenes: an internal view of shapes; an external view of shapes; an external view of horizontal lines; a ‘real’ three-dimensional external view; no view (blindfolded); or an internal collimated view of shapes. Variations in the visual scene had no significant effect on motion sickness caused by 0.1 Hz fore-and-aft oscillation with an acceleration magnitude of 0.89 ms-2 r.m.s. The absence of an influence of vision differs from the effects of the visual scene on motion sickness in cars and coaches and suggested that carsickness is not solely caused by low frequency fore-and-aft acceleration. In a second experiment, six groups of 20 subjects were exposed to 0.1 Hz fore-and-aft oscillation combined with 0.1 Hz pitch oscillation with a peak pitch displacement of 3.69°. For three groups of subjects, the pitch displacement was 180° out-of-phase with the fore-and-aft displacement, such that the resultant peak acceleration acting on subjects in the fore-and-aft direction was 1.89 ms-2. The other three groups of subjects experienced the same fore-and-aft and pitch oscillations, but presented out-of-phase so that the peak fore-and-aft acceleration of ±1.26 ms-2 r.m.s. was partially offset by the pitch displacement of ±3.69°. Each subject experienced one of three viewing conditions from the first experiment: internal, blindfolded or external. The visual scene influenced the motion sickness caused by combined fore-and-aft and pitch oscillation regardless of whether pitch motion was in-phase or out-of-phase with the fore-and-aft motion: there was less sickness with an external forward view than with either an internal view or a blindfold. The effect of the phase between the fore-and-aft and pitch motion depended on the visual scene: the phase influenced motion sickness with a blindfold and with internal viewing but not with external viewing. The effect of internal, blindfold and external viewing on motion sickness caused by 0.1, 0.2 and 0.4 Hz pitch oscillation was investigated in a third experiment with 180 subjects, 20 subjects in 9 conditions. The visual scene influenced motion sickness similarly with 0.1, 0.2, and 0.4 Hz pitch oscillation: external viewing reduced motion sickness relative to internal viewing. There was no significant effect of pitch oscillation frequency. Experimental results suggest that there is no effect of the visual scene on motion sickness caused by fore-and-aft oscillation but the visual scene is influential when pitch motion is part or all of the motion stimulus. The effect of the visual scene on motion sickness cannot be predicted without specifying the motion stimulus causing sickness. Unlike previous models of motion sickness, a conceptual model is suggested in which the expected visual signal is defined for a given vestibular input. The model predicts that external viewing reduces motion sickness relative to internal or blindfolded conditions when sickness is caused by motions inclusive of pitch oscillation. Model predictions for the effect of the visual scene on motion sickness caused by other directions of oscillation are considered.
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CHEN, HONGYI. "GPS-oscillation-robust Localization and Visionaided Odometry Estimation." Thesis, KTH, Maskinkonstruktion (Inst.), 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-247299.
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GPS/IMU integrated systems are commonly used for vehicle navigation. The algorithm for this coupled system is normally based on Kalman filter. However, oscillated GPS measurements in the urban environment can lead to localization divergence easily. Moreover, heading estimation may be sensitive to magnetic interference if it relies on IMU with integrated magnetometer. This report tries to solve the localization problem on GPS oscillation and outage, based on adaptive extended Kalman filter(AEKF). In terms of the heading estimation, stereo visual odometry(VO) is fused to overcome the effect by magnetic disturbance. Vision-aided AEKF based algorithm is tested in the cases of both good GPS condition and GPS oscillation with magnetic interference. Under the situations considered, the algorithm is verified to outperform conventional extended Kalman filter(CEKF) and unscented Kalman filter(UKF) in position estimation by 53.74% and 40.09% respectively, and decrease the drifting of heading estimation.GPS/IMU integrerade system används ofta för navigering av fordon. Algoritmen för detta kopplade system är normalt baserat på ett Kalmanfilter. Ett problem med systemet är att oscillerade GPS mätningar i stadsmiljöer enkelt kan leda till en lokaliseringsdivergens. Dessutom kan riktningsuppskattningen vara känslig för magnetiska störningar om den är beroende av en IMU med integrerad magnetometer. Rapporten försöker lösa lokaliseringsproblemet som skapas av GPS-oscillationer och avbrott med hjälp av ett adaptivt förlängt Kalmanfilter (AEKF). När det gäller riktningsuppskattningen används stereovisuell odometri (VO) för att försvaga effekten av magnetiska störningar genom sensorfusion. En Visionsstödd AEKF-baserad algoritm testas i fall med både goda GPS omständigheter och med oscillationer i GPS mätningar med magnetiska störningar. Under de fallen som är aktuella är algoritmen verifierad för att överträffa det konventionella utökade Kalmanfilteret (CEKF) och ”Unscented Kalman filter” (UKF) när det kommer till positionsuppskattning med 53,74% respektive 40,09% samt minska fel i riktningsuppskattningen.
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Tallon-Baudry, Catherine. "Rôle des oscillations 40 Hz dans l'intégration de l'information visuelle : étude électro- et magnéto-encéphalographique." Lyon 1, 1997. http://www.theses.fr/1997LYO1T061.
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Thillay, Alix. "Etude du traitement cérébral d'un contexte visuel prédictif dans l'autisme." Thesis, Tours, 2015. http://www.theses.fr/2015TOUR3314/document.
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Des réactions inhabituelles et disproportionnées face aux changements survenant de manière imprévisible dans l’environnement sont observées dans l’autisme. L’objectif de ce travail est de caractériser chez des adolescents et des jeunes adultes avec autisme les mécanismes neurophysiologiques impliqués dans le traitement d’un contexte visuel prédictif à partir de l’analyse des potentiels évoqués et des oscillations cérébrales. L’étude de la maturation au cours de l’adolescence chez le sujet au développement typique montre que les mécanismes de prédiction sont matures dès l’âge de 12 ans. Les personnes avec autisme parviennent à extraire l’information pertinente dans un contexte simple, certain et explicite, et à l’utiliser pour se préparer à la survenue d’un événement afin d’y avoir une réponse adaptée. Ces résultats suggèrent que les mécanismes de traitement d’un contexte visuel prédictif dans un contexte certain sont préservés dans l’autisme. Toutefois, les personnes avec autisme sur-anticipent les stimulations imprévisibles, en accord avec leur impression de surcharge sensorielle. Elles présentent également des difficultés pour moduler de manière flexible les activités corticales en fonction du niveau d’incertitude du contexte, en accord avec le défaut d’adaptation à un monde en perpétuel changement. Ce travail suggère qu’un dysfonctionnement des mécanismes de prédiction dans un contexte incertain pourrait fournir un cadre théorique permettant de mieux comprendre les particularités rencontrées dans l'autismeIndividuals with autism react in an unusual and disproportionate way if unpredictable changes occur in their environment. The aim of the present work is to investigate brain mechanisms involved in visual predictive context processing in adolescents and adults with autism using analysis of event-related potentials and brain oscillations. The developmental study shows that mechanisms of prediction are mature by the age of 12 in typically developing adolescents. Individuals with autism are able to extract relevant information from the stimulus train in a simple, certain and explicit context, to use it in order to anticipate the occurrence of an event and to have an appropriate response, suggesting preserved extraction and use of predictive information during a certain context. However, individuals with autism over-anticipate stimuli during an uncertain context, consistent with the sense of being overwhelmed by incoming information, and also cannot flexibly modulate cortical activity according to changing levels of uncertainty, in agreement with atypical adaptation in an ever-changing world. This work suggests that a dysfunction of predictive processing in an uncertain context might provide a theoretical framework to better understand the symptoms encountered in autism
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Herculano-Houzel, Suzana. "Modulation of neuronal synchronous oscillations : dynamic variation with level of cortical activation and long-term use-dependent modification." Paris 6, 1999. http://www.theses.fr/1999PA066610.
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Magazzini, Lorenzo. "Quality control of visual gamma oscillation frequency in studies of pharmacology, cognitive neuroscience and large-scale multi-site collaborations." Thesis, Cardiff University, 2016. http://orca.cf.ac.uk/98613/.
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In visual cortex, high-contrast grating stimuli induce neurons to oscillate synchronously with a centre frequency in the gamma range (~30–80 Hz). The peak frequency of visual gamma oscillations is modulated by numerous factors, including stimulus properties, cortical architecture and genetics, however, it can be measured reliably over time. As demonstrated by both animal models and human pharmacological studies, the gamma peak frequency is determined by the excitation/inhibition balance and the time constants of GABAergic processes. This oscillatory parameter could thus reflect inter-individual differences in cortical function/physiology, representing a possible biomarker for pharmacological treatment in conditions such as epilepsy, autism and schizophrenia. This thesis demonstrates the importance of measuring the gamma peak frequency accurately and reliably in magnetoencephalographic (MEG) recordings. In Chapter 2, a novel quality-control (QC) approach was validated for peak frequency estimation and identification of poor-quality data. In Chapter 3, QC of a previous pharmacological MEG study of visual gamma with tiagabine revealed a marked drug-induced reduction of peak frequency. Although contrasting with the null finding originally reported (Muthukumaraswamy et al., 2013), the result is supported by both animal models and recent human studies, demonstrating the potentialities of appropriate QC routines. In Chapter 4, testing for the effect of spatial attention on the gamma peak frequency in primary visual cortex resulted in no evidence of a change. However, the modulation of gamma amplitude by attention was consistent with a role in feed-forward signal propagation across the visual hierarchy. In Chapter 5, the QC approach was used to compare visual gamma data recorded at different sites of the UK MEG Partnership, demonstrating the feasibility of combining data from different MEG systems. These results have implications particularly for pharmacological and large-scale multi-site studies, both of which are emerging as promising approaches for the study of brain function with MEG.
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Chow, Eric Ho Chi. "Postural disturbance and vection when viewing visual stimulus oscillating in roll and fore-and-aft directions : effects of frequency and peak velocity /." View abstract or full-text, 2008. http://library.ust.hk/cgi/db/thesis.pl?IELM%202008%20CHOW.
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Koenig, Roger. "Comment le sens est-il extrait de l'information visuelle ? Le système visuel exploré des catégories à la conscience." Phd thesis, Université Paul Sabatier - Toulouse III, 2012. http://tel.archives-ouvertes.fr/tel-00736494.
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Comment le sens est-il extrait de l'information visuelle ? Cette thèse est focalisée sur la capacité du système visuel d'humains et de singes à extraire et représenter l'information visuelle sur différents niveaux de complexité. Nous avons étudié différent niveaux de représentations visuelles, de la production de représentations visuelles primaires jusqu'à l'élaboration de représentations visuelles conscientes. Ce manuscrit présente six travaux dans lesquels nous avons exploré : (1) les attributs visuels nécessaires pour réaliser la tâche de catégorisation ultra-rapide chez l'homme et le singe au moyen de méthodes psychophysiques, (2) la dynamique spatio-temporelle de l'attention visuelle chez l'homme au moyen de méthodes psychophysiques, (3) les corrélats neuronaux des représentations de haut niveau en EEG grâce au développement d'une nouvelle technique appelée SWIFT, (4) les corrélats neuronaux de la conscience visuelle dans la rivalité binoculaire en EEG, (5) la synchronie des signaux cérébraux en fonction de la reconnaissance consciente au moyen d'enregistrements intracrâniens chez des patients épileptiques et (6) les corrélats neuronaux associés à la prise de conscience chez le singe au moyen d'enregistrements intracrâniens. Les résultats de ces travaux nous ont permis d'ébaucher un modèle de la perception visuelle, cherchant à dissocier l'attention et la conscience.
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Koenig, Alexis Roger. "Comment le sens est-il extrait de l'information visuelle ? : le système visuel exploré des catégories à la conscience." Toulouse 3, 2012. http://thesesups.ups-tlse.fr/1749/.
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Comment le sens est-il extrait de l'information visuelle ? Cette thèse est focalisée sur la capacité du système visuel d'humains et de singes à extraire et représenter l'information visuelle sur différents niveaux de complexité. Nous avons étudié différent niveaux de représentations visuelles, de la production de représentations visuelles primaires jusqu'à l'élaboration de représentations visuelles conscientes. Ce manuscrit présente six travaux dans lesquels nous avons exploré : (1) les attributs visuels nécessaires pour réaliser la tâche de catégorisation ultra rapide chez l'homme et le singe au moyen de méthodes psychophysiques, (2) la dynamique spatio-temporelle de l'attention visuelle chez l'homme au moyen de méthodes psychophysiques, (3) les corrélats neuronaux des représentations de haut niveau en EEG grâce au développement d'une nouvelle technique appelée SWIFT, (4) les corrélats neuronaux de la conscience visuelle dans la rivalité binoculaire en EEG, (5) la synchronie des signaux cérébraux en fonction de la reconnaissance consciente au moyen d'enregistrements intracrâniens chez des patients épileptiques et (6) les corrélats neuronaux associés à la prise de conscience chez le singe au moyen d'enregistrements intracrâniens. Les résultats de ces travaux nous ont permis d'ébaucher un modèle de la perception visuelle cherchant à dissocier l'attention et la conscienceHow does sense emerges in the visual system? In this thesis we will be focused on the visual system of human and non-human primates and their large capacity of extract and represent visual information. We studied several levels of visual representations from those related to the extraction of coarse visual features to the emergence of conscious visual representations. This manuscript presents six works in which we explored: (1) the visual features necessary to perform ultra-rapid visual categorization in monkeys and humans using psychophysics, (2) the spatio-temporal dynamics of visual attention in humans using psychophysics, (3) the neural correlates of high-level visual representations using EEG tanks to the development of an innovative technique called SWIFT, (4) the neural correlates of visual consciousness under binocular rivalry using EEG, (5) the synchrony of brain signals as a function of conscious recognition using intracranial electrodes implanted in epileptic patients and (6) the neural correlates associated with conscious perception in monkeys using intracranial electrodes. The results of these works allowed outlining a tentative model of visual perception aimed to dissociate attention and consciousness
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Chaumon, Maximilien. "Apprentissage implicite du contexte visuel et guidage de la perception : Expériences MEG et EEG intracrânien." Phd thesis, Université Pierre et Marie Curie - Paris VI, 2008. http://tel.archives-ouvertes.fr/tel-00310152.
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Le contexte guide la perception de manière inconsciente. En vision, il est utilisé pour faciliter la reconnaissance et la recherche d'objets. Nous avons élaboré un protocole expérimental nouveau pour étudier l'influence du contexte sur la recherche visuelle en magnéto-encéphalographie (MEG). Une étude chez des sujets sains nous a permis d'observer les étapes de l'apprentissage et de l'exploitation des relations spatiales entre le contexte et la cible en recherche visuelle. Lorsque le contexte peut être utilisé pour prédire la position de la cible, une activité oscillatoire spécifique dans la bande de fréquence gamma (30-48 Hz) se développe dès qu'une image est vue pour la deuxième fois (Chaumon, Schwartz et Tallon-Baudry, En révision). Lorsque les sujets commencent à utiliser les régularités inconsciemment, ces oscillations gamma disparaissent et laissent place à un effet dans l'activité évoquée en MEG avant 100 ms (Chaumon, Drouet et Tallon-Baudry, 2008). Des enregistrements effectués dans la même tâche chez des patients épileptiques implantés d'électrodes intracrâniennes confirment les résultats MEG et montrent que les régions du lobe temporal antérieur sont impliquées dans l'exploitation des relations entre contexte et cible (Chaumon, Adam, Hasboun et Tallon-Baudry, En préparation).Nous proposons que l'activité gamma permet la création et l'affûtage d'une représentation neuronale par des mécanismes de plasticité dépendante de la synchronie des potentiels d'action (spike timing dependent plasticity, STDP). Cette représentation une fois créée serait activée très rapidement pour biaiser le traitement cérébral, permettant la prise en compte de l'expérience vécue dès les étapes précoces du traitement sensoriel.
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Ossandon, Valdes Tomas. "A prefrontal-temporal network underlying state changes between Stimulus-Driven and Stimulus-Independent Cognition." Phd thesis, Université Claude Bernard - Lyon I, 2010. http://tel.archives-ouvertes.fr/tel-00726306.
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The brain displays moment-to-moment activity fluctuations that reflect various levels of engagement with the outside world. Processing external stimuli is not only associated with increased brain metabolism but also with prominent deactivation in specific structures, collectively known as the default-mode network (DMN). The role of the DMN remains enigmatic partly because its electrophysiological correlates and temporal dynamics are still poorly understood. Using unprecedented wide-spread depth recordings in epileptic patients, undergoing intracranial EEG during pre-surgical evaluation, we reveal that DMN neural populations display task-related suppressions of gamma (60-140 Hz) power and, critically, we show how millisecond temporal profile and amplitude of gamma deactivation tightly correlate with task demands and subject performance. The results show also that during an attentional task, sustained activations in the gamma band power are presented across large cortical networks, while transient activations are mostly specific to occipital and temporal regions. Our findings reveal a pivotal role for broadband gamma modulations in the interplay between activation and deactivation networks mediating efficient goal-directed behavior
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(8086100), Samuel T. Kissinger. "Visual experience-dependent oscillations in the mouse visual system." Thesis, 2019.
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The visual system is capable of interpreting immense sensory complexity, allowing us to quickly identify behaviorally relevant stimuli in the environment. It performs this task with a hierarchical organization that works to detect, relay, and integrate visual stimulus features into an interpretable form. To understand the complexities of this system, visual neuroscientists have benefited from the many advantages of using mice as visual models. Despite their poor visual acuity, these animals possess surprisingly complex visual systems, and have been instrumental in understanding how visual features are processed in the primary visual cortex (V1). However, a growing body of literature has shown that primary sensory areas like V1 are capable of more than basic feature detection, but can express neural activity patterns related to learning, memory, categorization, and prediction.
Visual experience fundamentally changes the encoding and perception of visual stimuli at many scales, and allows us to become familiar with environmental cues. However, the neural processes that govern visual familiarity are poorly understood. By exposing awake mice to repetitively presented visual stimuli over several days, we observed the emergence of low frequency oscillations in the primary visual cortex (V1). The oscillations emerged in population level responses known as visually evoked potentials (VEPs), as well as single-unit responses, and were not observed before the perceptual experience had occurred. They were also not evoked by novel visual stimuli, suggesting that they represent a new form of visual familiarity in the form of low frequency oscillations. The oscillations also required the muscarinic acetylcholine receptors (mAChRs) for their induction and expression, highlighting the importance of the cholinergic system in this learning and memory-based phenomenon. Ongoing visually evoked oscillations were also shown to increase the VEP amplitude of incoming visual stimuli if the stimuli were presented at the high excitability phase of the oscillations, demonstrating how neural activity with unique temporal dynamics can be used to influence visual processing.
Given the necessity of perceptual experience for the strong expression of these oscillations and their dependence on the cholinergic system, it was clear we had discovered a phenomenon grounded in visual learning or memory. To further validate this, we characterized this response in a mouse model of Fragile X syndrome (FX), the most common inherited form of autism and a condition with known visual perceptual learning deficits. Using a multifaceted experimental approach, a number of neurophysiological differences were found in the oscillations displayed in FX mice. Extracellular recordings revealed shorter durations and lower power oscillatory activity in FX mice. Furthermore, we found that the frequency of peak oscillatory activity was significantly decreased in FX mice, demonstrating a unique temporal neural impairment not previously reported in FX. In collaboration with Dr. Christopher J. Quinn at Purdue, we performed functional connectivity analysis on the extracellularly recorded spikes from WT and FX mice. This analysis revealed significant impairments in functional connections from multiple layers in FX mice after the perceptual experience; some of which were validated by another graduate student (Qiuyu Wu) using Channelrhodopsin-2 assisted circuit mapping (CRACM). Together, these results shed new light on how visual stimulus familiarity is differentially encoded in FX via persistent oscillations, and allowed us to identify impairments in cross layer connectivity that may underlie these differences.
Finally, we asked whether these oscillations are observable in other brain areas or are intrinsic to V1. Furthermore, we sought to determine if the oscillating unit populations in V1 possess uniform firing dynamics, or contribute differentially to the population level response. By performing paired recordings, we did not find prominent oscillatory activity in two visual thalamic nuclei (dLGN and LP) or a nonvisual area (RSC) connected to V1, suggesting the oscillations may not propagate with similar dynamics via cortico-thalamic connections or retrosplenial connections, but may either be uniquely distributed across the visual hierarchy or predominantly restricted to V1. Using K-means clustering on a large population of oscillating units in V1, we found unique temporal profiles of visually evoked responses, demonstrating distinct contributions of different unit sub-populations to the oscillation response dynamics.
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Barnes, William. "Reversible Visual Hemineglect: the Role of Neural Oscillations in Primary Visual Cortex." Phd thesis, 2016. https://tuprints.ulb.tu-darmstadt.de/5193/1/Thesis%20Barnes%20PDF%20Dec2015.pdf.
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Visual hemineglect is a pathology where damage to any of a number of areas in the brain can result in visual stimuli contralateral to neural damage not entering perceptual awareness. In the cat, the superior colliculus (SC) and cortical areas on the medial bank of posterior middle suprasylvian sulcus (pMS) are regions that when unilaterally damaged result in contralateral visual hemineglect. In this dissertation, electrophysiological recordings of population activity in cat primary visual cortex were made while either the SC or pMS were deactivated. The goal of this experimental set- up was to ascertain the effects of SC or pMS deactivation on the electrophysiological population signal as a visual stimulus enters the cortical processing network at its main entry point, primary visual cortex. Four projects were executed for this thesis involving: 1) anesthetized SC-deactivation, 2) anesthetized pMS-deactivation, 3) awake pMS deactivation, and 4) pMS-deactivation in the awake-behaving cat. Advanced recording techniques to monitor neural activity in the awake-behaving cat (project 4) while cortex was both active and deactivated were developed for this thesis to compliment thesis projects 1-3 involving classical recording techniques in animals passively viewing a square-wave visual stimulus.
The results are as follows: in the awake cat performing a visual perimetry task (project 4), neural activity when 1) unilateral pMS was deactivated and contralateral stimuli neglected versus when 2) pMS was active and stimuli were attended, reveals a significant drop in high-frequency gamma (52-90 Hz) oscillations and low-frequency theta (4-8 Hz) oscillations bilaterally in primary visual cortex.
The drop in gamma and theta power was mirrored in anesthetized recordings during pMS deactivation (project 2). In this experimental set-up the cat was anesthetized and square-wave gratings were used as a visual stimulation. Gamma and theta power decreased during pMS deactivation relative to the condition where pMS was active. A similar trend, though statistically insignificant, were made when performing the same experiment as project 2, but in awake cats (project 3). The lack of statistical significance is presumably due to increased ongoing, internally generated, activity in the awake preparation.
The findings in projects 2 & 3 confirm the visual perimetry finding in project 4 with the caveat that the passive viewing projects 2 & 3 yield a cooling-induced interhemispheric imbalance in theta and gamma power, whereas power changes for the awake-behaving cat in project 4 were bilateral with no interhemispheric imbalance. The strong unilateral effect in project 2 is presumably due to anesthesia inhibiting interareal interaction, or could as-well reflect reduced processing demands relative to the perimetry task. The perimerty task is a behavioral task and may necessitate the recruiting of a larger network involving both hemispheres in order to orient attention to a low-salience LED located in the visual periphery.
The anesthetized project was repeated, but with SC rather than pMS deactivation (thesis project 1). The SC deactivation led to an ipso deactivation loss of gamma, but not theta power.
Taken together, the meaning of the results in projects 1-4 is as follows: unilateral deactivation of the pMS or SC results in a visual hemineglect in the awake behaving animal. Unilateral deactivation of either structure also leads to a loss of gamma power. This loss in gamma power during pMS or SC deactivation lends support to the binding by synchrony hypothesis (Gray et al 1989) whereby high-frequency oscillations act as a carrier frequency through which a larger cortical network can represent a stimulus via synchronous activity in the disparate neural processing nodes. Along this line, loss of gamma power would indicate a break-down in network communication that leads to a neglect of contralateral visual stimuli. A cooling induced interhemispheric imbalance in gamma power, as found in passive-viewing projects 1-3, could explain visual hemineglect because the primary visual cortex respresenting the neglected hemifield has less gamma power than the hemisphere responsible for the intact visual hemispace. However, interhemispheric gamma power imbalance does not occur in the behaving cat. In light of a bilateral loss of gamma power for neglect trials following pMS inactivation in project 4, an explanation beyond interhemispheric gamma power imbalance must be formed to explain behavioral hemineglect, at least with regards to pMS inactivation
The loss of theta power for pMS but not SC deactivation lends support to the attention to memory hypothesis (Cabeza et al 2008). This hypothesis views the posterior parietal cortex (PPC), of which pMS is a part, as an area involved in directing attention to internal memories and goals. Anatomical links between the PPC and the hippocampus, where a theta rhythm is generated, may implicate the pMS in more than just reflexive orienting behavior. Moreover, posterior parietal cortex, of which pMS is a key part, is known from anatomical studies (Markov et al 2014) to be one of the network hubs in the brain The loss of theta power following pMS deactivation may indicate a global loss network connectivity with one result being a loss in the ability to create an egocentric coordinate system in the hemispace contralateral to pMS deactivation. Deactivation of the pMS could also lead to a context dependent loss in the ability to retain awareness that behaviorally relevant stimuli have occurred in the hemispace contralateral to pMS deactivation. Both spatial coordinates and memories are functions inextricably intertwined with the hippocampus. Moreover, cross- frequency coupling between theta and gamma is well established. This frequency coupling, with small amplitude gamma oscillation riding on top of large-amplitude theta oscillations, would allow the membrane potentials in participating distributed brain regions to depolarize and simultaneously spike thereby generating a distributed neural signature that could underly perceptual awareness. This binding mechanism appears to be compromised in visual hemineglect.
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BENEDETTO, ALESSANDRO. "The temporal dynamics of vision for action and perception." Doctoral thesis, 2017. http://hdl.handle.net/2158/1079075.
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The aim of the present thesis is to investigate the mechanisms of sensorimotor integration, and - in particular - the role of oscillations in action and perception. In the first study, we considered the contrast sensitivity dynamics during the execution of free saccades. We tested the hypothesis that a voluntary eye movement could trigger behavioral oscillations, with the aim to study in depth the properties of these perceptual rhythmicity. The second study investigated the effect of saccades on the pupillary response. We studied the perceptual and the
pupillary dynamics at around the time of a saccade, looking for possible correlation between the perceptual response and the pupillary
constriction. In the third study, we moved to analyze the effect of a simple hand action (button press) over contrast sensitivity, investigating
also some possible modulatory effects of ambient luminance. Finally, in the fourth study (comprising three experiments), we enucleated the
modulatory effects of ambient luminance via an electrophysiological and psychophysical investigation. A general conclusion will sum up the
present findings shown here, suggesting possible future directions.
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Bharmauria, Vishal. "Investigating the encoding of visual stimuli by forming neural circuits in the cat primary visual cortex." Thèse, 2016. http://hdl.handle.net/1866/14129.
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Contexte
La connectomique, ou la cartographie des connexions neuronales, est un champ de recherche des neurosciences évoluant rapidement, promettant des avancées majeures en ce qui concerne la compréhension du fonctionnement cérébral. La formation de circuits neuronaux en réponse à des stimuli environnementaux est une propriété émergente du cerveau. Cependant, la connaissance que nous avons de la nature précise de ces réseaux est encore limitée. Au niveau du cortex visuel, qui est l’aire cérébrale la plus étudiée, la manière dont les informations se transmettent de neurone en neurone est une question qui reste encore inexplorée. Cela nous invite à étudier l’émergence des microcircuits en réponse aux stimuli visuels. Autrement dit, comment l’interaction entre un stimulus et une assemblée cellulaire est-elle mise en place et modulée?
Méthodes
En réponse à la présentation de grilles sinusoïdales en mouvement, des ensembles neuronaux ont été enregistrés dans la couche II/III (aire 17) du cortex visuel primaire de chats anesthésiés, à l’aide de multi-électrodes en tungstène. Des corrélations croisées ont été effectuées entre l’activité de chacun des neurones enregistrés simultanément pour mettre en évidence les liens fonctionnels de quasi-synchronie (fenêtre de ± 5 ms sur les corrélogrammes croisés corrigés). Ces liens fonctionnels dévoilés indiquent des connexions synaptiques putatives entre les neurones. Par la suite, les histogrammes peri-stimulus (PSTH) des neurones ont été comparés afin de mettre en évidence la collaboration synergique temporelle dans les réseaux fonctionnels révélés. Enfin, des spectrogrammes dépendants du taux de décharges entre neurones ou stimulus-dépendants ont été calculés pour observer les oscillations gamma dans les microcircuits émergents. Un indice de corrélation (Rsc) a également été calculé pour les neurones connectés et non connectés.
Résultats
Les neurones liés fonctionnellement ont une activité accrue durant une période de 50 ms contrairement aux neurones fonctionnellement non connectés. Cela suggère que les connexions entre neurones mènent à une synergie de leur inter-excitabilité. En outre, l’analyse du spectrogramme dépendant du taux de décharge entre neurones révèle que les neurones connectés ont une plus forte activité gamma que les neurones non connectés durant une fenêtre d’opportunité de 50ms. L’activité gamma de basse-fréquence (20-40 Hz) a été associée aux neurones à décharge régulière (RS) et l’activité de haute fréquence (60-80 Hz) aux neurones à décharge rapide (FS). Aussi, les neurones fonctionnellement connectés ont systématiquement un Rsc plus élevé que les neurones non connectés. Finalement, l’analyse des corrélogrammes croisés révèle que dans une assemblée neuronale, le réseau fonctionnel change selon l’orientation de la grille. Nous démontrons ainsi que l’intensité des relations fonctionnelles dépend de l’orientation de la grille sinusoïdale. Cette relation nous a amené à proposer l’hypothèse suivante : outre la sélectivité des neurones aux caractères spécifiques du stimulus, il y a aussi une sélectivité du connectome. En bref, les réseaux fonctionnels «signature » sont activés dans une assemblée qui est strictement associée à l’orientation présentée et plus généralement aux propriétés des stimuli.
Conclusion
Cette étude souligne le fait que l’assemblée cellulaire, plutôt que le neurone, est l'unité fonctionnelle fondamentale du cerveau. Cela dilue l'importance du travail isolé de chaque neurone, c’est à dire le paradigme classique du taux de décharge qui a été traditionnellement utilisé pour étudier l'encodage des stimuli. Cette étude contribue aussi à faire avancer le débat sur les oscillations gamma, en ce qu'elles surviennent systématiquement entre neurones connectés dans les assemblées, en conséquence d’un ajout de cohérence. Bien que la taille des assemblées enregistrées soit relativement faible, cette étude suggère néanmoins une intrigante spécificité fonctionnelle entre neurones interagissant dans une assemblée en réponse à une stimulation visuelle. Cette étude peut être considérée comme une prémisse à la modélisation informatique à grande échelle de connectomes fonctionnels.Background ‘Connectomics’— the mapping of neural connections, is a rapidly advancing field in neurosciences and it promises significant insights into the brain functioning. The formation of neuronal circuits in response to the sensory environment is an emergent property of the brain; however, the knowledge about the precise nature of these sub-networks is still limited. Even at the level of the visual cortex, which is the most studied area in the brain, how sensory inputs are processed between its neurons, is a question yet to be completely explored. Heuristically, this invites an investigation into the emergence of micro-circuits in response to a visual input — that is, how the intriguing interplay between a stimulus and a cell assembly is engineered and modulated? Methods Neuronal assemblies were recorded in response to randomly presented drifting sine-wave gratings in the layer II/III (area 17) of the primary visual cortex (V1) in anaesthetized cats using tungsten multi-electrodes. Cross-correlograms (CCGs) between simultaneously recorded neural activities were computed to reveal the functional links between neurons that were indicative of putative synaptic connections between them. Further, the peristimulus time histograms (PSTH) of neurons were compared to divulge the epochal synergistic collaboration in the revealed functional networks. Thereafter, perievent spectrograms were computed to observe the gamma oscillations in emergent microcircuits. Noise correlation (Rsc) was calculated for the connected and unconnected neurons within these microcircuits. Results The functionally linked neurons collaborate synergistically with augmented activity in a 50-ms window of opportunity compared with the functionally unconnected neurons suggesting that the connectivity between neurons leads to the added excitability between them. Further, the perievent spectrogram analysis revealed that the connected neurons had an augmented power of gamma activity compared with the unconnected neurons in the emergent 50-ms window of opportunity. The low-band (20-40 Hz) gamma activity was linked to the regular-spiking (RS) neurons, whereas the high-band (60-80 Hz) activity was related to the fast-spiking (FS) neurons. The functionally connected neurons systematically displayed higher Rsc compared with the unconnected neurons in emergent microcircuits. Finally, the CCG analysis revealed that there is an activation of a salient functional network in an assembly in relation to the presented orientation. Closely tuned neurons exhibited more connections than the distantly tuned neurons. Untuned assemblies did not display functional linkage. In short, a ‘signature’ functional network was formed between neurons comprising an assembly that was strictly related to the presented orientation. Conclusion Indeed, this study points to the fact that a cell-assembly is the fundamental functional unit of information processing in the brain, rather than the individual neurons. This dilutes the importance of a neuron working in isolation, that is, the classical firing rate paradigm that has been traditionally used to study the encoding of a stimulus. This study also helps to reconcile the debate on gamma oscillations in that they systematically originate between the connected neurons in assemblies. Though the size of the recorded assemblies in the current investigation was relatively small, nevertheless, this study shows the intriguing functional specificity of interacting neurons in an assembly in response to a visual input. One may form this study as a premise to computationally infer the functional connectomes on a larger scale.
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Mikulskaya, Elena. "Visual processing, visual attention and their neural correlates in early-onset cannabis users." Thesis, 2016. http://hdl.handle.net/1959.13/1312742.
Full textAbstract:
Research Doctorate - Doctor of Philosophy (PhD)Cannabis use worldwide has been increasing steadily over the past decade. The current trend towards legalization of cannabis for medical purposes and/or recreational use increases the potential to expose more and younger people to cannabis. Early age of onset has been linked to visual and attentional deficits in adulthood suggested to arise from blunted dopaminergic functioning. Dopamine is a neurotransmitter, critically important for efficient visual and attentional functioning in addition to general cognitive and motor behaviour. The overall aim of this thesis was to investigate in depth low level visual processing (Phase 1) and visual attention and underlying neural processing (Phase 2) in early-onset cannabis users. Static and dynamic contrast thresholds were examined in Experiments 1 and 2 and motion discrimination thresholds were examined in Experiment 3 under normal and low luminance conditions. An index of brain dopamine production was also collected and compared in Experiment 4. Static but not dynamic contrast detection thresholds were significantly higher in the cannabis group (21 participants: 18 of whom commenced cannabis use before the age of 17) compared to the control group (20 participants) under mesopic levels of luminance. Both static and dynamic contrast thresholds were positively correlated with frequency of use in the cannabis group. Discrimination of direction of translational and radial motion was examined in Experiment 3 under normal and mesopic luminance and at two levels of stimuli contrast: 12 and 24%. Independently of luminance level and motion type, coherence thresholds were significantly higher in the cannabis group at 24% stimuli contrast compared to the control group and in particular the thresholds were higher for radial compared to translational motion, although the differences failed to reach statistical significance. Again, the thresholds in the cannabis group were higher with more frequent cannabis use. We also found significantly lower spontaneous Eye Blink Rate (EBR) in the cannabis group compared to the control group in Experiment 4. We argued that lower dopamine may underlie the higher thresholds shown by the cannabis group across all visual tasks in Phase 1. In Phase 2 of this thesis behavioural data and EEG recordings were collected from 53 participants in four experiments. ERPs and gamma band activity were extracted from EEG recordings and compared between the control group (29 participants) and the cannabis group (24 participants: all commenced cannabis use before age 17). In Experiment 5 we investigated the neural correlates (ERPs and gamma band activity) of radial motion processing to further investigate the results of Experiment 3. As expected reduced ERP amplitudes to motion stimuli were shown by the cannabis group compared to the control group. Motion stimuli were also employed in the oddball task in Experiment 6 in which we aimed to investigate the neural correlates of selective attention. The cannabis group showed significant reductions in P3b amplitude in response to target stimuli, overall reduced amplitude and delayed latency of P3b, and increased connectivity in the gamma range to target and standard stimuli. Increased connectivity for both types of stimuli was argued to compensate for reduced attentional resource allocation, as indexed by reduced P3b amplitudes in the cannabis group. Cannabis related and neutral words were used in a word recognition task in Experiment 7, with target words presented briefly, then presented paired with a distractor for recognition. Cannabis and neutral pictures used as primes followed by cannabis and neutral words in a lexical decision task were employed in Experiment 8. We found some evidence for cannabis biased attention in the cannabis group, as indexed by differences in ERP components and the connectivity patterns in gamma band activity. Overall, in both experiments, the cannabis group showed increased processing effort toward both cannabis and neutral stimuli. The current thesis has demonstrated that visual processing, attention and underlying brain activity are altered by cannabis use with early age of onset. Consistent with previous research, selective attention and its neural correlates differed in respect to stimuli identity, cannabis or neutral, in early-onset cannabis users. It has also been shown that cannabis related stimuli, presented at subliminal levels, influenced attention and subsequent processing of cannabis and neutral stimuli in the cannabis group. Future investigations could examine in depth the effects of early-onset cannabis use on visual processing and attention, and whether and how it is modulated by concomitant reductions in dopamine.
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Moratti, Stephan [Verfasser]. "Modulation of stimulus driven neuronal oscillations by the emotional and motivational significance of visual stimuli / vorgelegt von Stephan Moratti." 2005. http://d-nb.info/975676911/34.
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"Neural Mechanisms of Sensory Integration: Frequency Domain Analysis of Spike and Field Potential Activity During Arm Position Maintenance with and Without Visual Feedback." Doctoral diss., 2017. http://hdl.handle.net/2286/R.I.46363.
Full textAbstract:
abstract: Understanding where our bodies are in space is imperative for motor control, particularly for actions such as goal-directed reaching. Multisensory integration is crucial for reducing uncertainty in arm position estimates. This dissertation examines time and frequency-domain correlates of visual-proprioceptive integration during an arm-position maintenance task. Neural recordings were obtained from two different cortical areas as non-human primates performed a center-out reaching task in a virtual reality environment. Following a reach, animals maintained the end-point position of their arm under unimodal (proprioception only) and bimodal (proprioception and vision) conditions. In both areas, time domain and multi-taper spectral analysis methods were used to quantify changes in the spiking, local field potential (LFP), and spike-field coherence during arm-position maintenance.
In both areas, individual neurons were classified based on the spectrum of their spiking patterns. A large proportion of cells in the SPL that exhibited sensory condition-specific oscillatory spiking in the beta (13-30Hz) frequency band. Cells in the IPL typically had a more diverse mix of oscillatory and refractory spiking patterns during the task in response to changing sensory condition. Contrary to the assumptions made in many modelling studies, none of the cells exhibited Poisson-spiking statistics in SPL or IPL.
Evoked LFPs in both areas exhibited greater effects of target location than visual condition, though the evoked responses in the preferred reach direction were generally suppressed in the bimodal condition relative to the unimodal condition. Significant effects of target location on evoked responses were observed during the movement period of the task well.
In the frequency domain, LFP power in both cortical areas was enhanced in the beta band during the position estimation epoch of the task, indicating that LFP beta oscillations may be important for maintaining the ongoing state. This was particularly evident at the population level, with clear increase in alpha and beta power. Differences in spectral power between conditions also became apparent at the population level, with power during bimodal trials being suppressed relative to unimodal. The spike-field coherence showed confounding results in both the SPL and IPL, with no clear correlation between incidence of beta oscillations and significant beta coherence.Dissertation/Thesis
Doctoral Dissertation Biomedical Engineering 2017
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Ferrandez, Roxanne. "Profil temporel de l’efficacité du traitement visuel en reconnaissance d’objets et de visages." Thèse, 2019. http://hdl.handle.net/1866/23828.
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Les variations d’efficacité du traitement visuel dans le temps ont été étudiées par échantillonnage temporel aléatoire. Vingt-quatre adultes ont identifié des stimuli composés de bruit blanc visuel et d’images d’objets familiers (expérience 1) ou de visages célèbres (expérience 2). Le ratio signal-bruit variait à travers le temps selon des fonctions d’échantillonnage générées par l’intégration d’ondes sinusoïdales de différentes fréquences (5 à 55 Hz) et de phases et amplitudes aléatoires. Des vecteurs de classification (VC) temporels ont été calculés en soustrayant la somme pondérée des ratios signal-bruit associés aux mauvaises réponses de celle associée aux bonnes réponses. Des images de classification (IC) temps-fréquence ont été obtenues en appliquant la même procédure aux résultats d’analyses temps-fréquence réalisées sur la fonction d’échantillonnage de chaque essai. Les VC temporels des deux expériences sont très variables entre les participants. Par contre, les IC temps-fréquence sont remarquablement similaires à travers les participants (cohérence inter-sujets de .93 et .57 pour l’expérience 1 et 2 respectivement). Des comparaisons par test t nous indiquent de nombreuses différences entre les IC temps-fréquence des objets et visages familiers, mais aussi des objets non familiers et des mots analysés dans des études précédentes. Ainsi, ces IC sont sensibles à la classe de stimuli présentés, mais aussi à la familiarité de ces derniers. Les résultats témoignent d’une variation rapide dans l’efficacité de l’encodage visuel durant les 200 premières millisecondes d’exposition au stimulus et suggèrent que les IC du domaine temps-fréquence reflètent un aspect hautement fondamental du traitement visuel, hypothétiquement rattaché aux oscillations cérébrales.Variations in visual processing effectiveness through time were investigated using random temporal stimulus sampling. Twenty-four adults named photographs of either familiar objects (experiment 1) or famous faces (experiment 2). Stimuli were made by a linear combination of the target image and high density white visual noise. Signal-to-noise ratio varied throughout the 200 ms stimulus duration. A new temporal sampling function was generated on each trial by the integration of random amplitude and phase sinusoidal waves of frequency between 5 and 55 Hz (in 5 Hz steps). Temporal classification vectors (CV) were calculated by subtracting the weighted sum of the signal-to-noise ratio associated to errors from that associated to correct responses. Time-frequency classification images (CI) were obtained by applying the same procedure on the outcome of time-frequency analyses applied to the sampling functions of each trial. In both experiments, the temporal CVs were highly variable across participants, but the time-frequency CIs were remarkably similar across participants (inter-subject coherence of .93 and .57 for experiments 1 and 2 respectively). T-tests revealed multiple differences between the time-frequency CIs obtained with familiar objects and faces, but also with non-familiar objects and words analyzed in previous studies. Therefore, theses CIs are sensitive to stimulus type, but also to stimulus familiarity. The present results indicate rapid variations of visual encoding effectiveness in the initial 200 ms of stimulus exposure and suggests that the time-frequency CIs tap a highly fundamental aspect of visual processing, hypothetically linked to brain oscillations.
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(10531388), Alexandr Pak. "CONTEXTUAL MODULATION OF NEURAL RESPONSES IN THE MOUSE VISUAL SYSTEM." Thesis, 2021.
Find full textAbstract:
The visual system is responsible for processing visual input, inferring its environmental causes, and assessing its behavioral significance that eventually relates to visual perception and guides animal behavior. There is emerging evidence that visual perception does not simply mirror the outside world but is heavily influenced by contextual information. Specifically, context might refer to the sensory, cognitive, and/or behavioral cues that help to assess the behavioral relevance of image features. One of the most famous examples of such behavior is visual or optical illusions. These illusions contain sensory cues that induce a subjective percept that is not aligned with the physical nature of the stimulation, which, in turn, suggests that a visual system is not a passive filter of the outside world but rather an active inference machine.
Such robust behavior of the visual system is achieved through intricate neural computations spanning several brain regions that allow dynamic visual processing. Despite the numerous attempts to gain insight into those computations, it has been challenging to decipher the circuit-level implementation of contextual processing due to technological limitations. These questions are of great importance not only for basic research purposes but also for gaining deeper insight into neurodevelopmental disorders that are characterized by altered sensory experiences. Recent advances in genetic engineering and neurotechnology made the mouse an attractive model to study the visual system and enabled other researchers and us to gain unprecedented cellular and circuit-level insights into neural mechanisms underlying contextual processing.
We first investigated how familiarity modifies the neural representation of stimuli in the mouse primary visual cortex (V1). Using silicon probe recordings and pupillometry, we probed neural activity in naive mice and after animals were exposed to the same stimulus over the course of several days. We have discovered that familiar stimuli evoke low-frequency oscillations in V1. Importantly, those oscillations were specific to the spatial frequency content of the familiar stimulus. To further validate our findings, we investigated how this novel form of visual learning is represented in serotonin-transporter (SERT) deficient mice. These transgenic animals have been previously found to have various neurophysiological alterations. We found that SERT-deficient animals showed longer oscillatory spiking activity and impaired cortical tuning after visual learning. Taken together, we discovered a novel phenomenon of familiarity-evoked oscillations in V1 and utilized it to reveal altered perceptual learning in SERT-deficient mice.
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Next, we investigated how spatial context influences sensory processing. Visual illusions provide a great opportunity to investigate spatial contextual modulation in early visual areas. Leveraging behavioral training, high-density silicon probe recordings, and optogenetics, we provided evidence for an interplay of feedforward and feedback pathways during illusory processing in V1. We first designed an operant behavioral task to investigate illusory perception in mice. Kanizsa illusory contours paradigm was then adapted from primate studies to mouse V1 to elucidate neural correlates of illusory responses in V1. These experiments provided behavioral and neurophysiological evidence for illusory perception in mice. Using optogenetics, we then showed that suppression of the lateromedial area inhibits illusory responses in mouse V1. Taken together, we demonstrated illusory responses in mice and their dependence on the top-down feedback from higher-order visual areas.
Finally, we investigated how temporal context modulates neural responses by combining silicon probe recordings and a novel visual oddball paradigm that utilizes spatial frequency filtered stimuli. Our work extended prior oddball studies by investigating how adaptation and novelty processing depends on the tuning properties of neurons and their laminar position. Furthermore, given that reduced adaptation and sensory hypersensitivity are one of the hallmarks of altered sensory experiences in autism, we investigated the effects of temporal context on visual processing in V1 of a mouse model of fragile X syndrome (FX), a leading monogenetic cause of autism. We first showed that adaptation was modulated by tuning properties of neurons in both genotypes, however, it was more confined to neurons preferring the adapted feature in FX mice. Oddball responses, on the other hand, were modulated by the laminar position of the neurons in WT with the strongest novelty responses in superficial layers, however, they were uniformly distributed across the cortical column in FX animals. Lastly, we observed differential processing of omission responses in FX vs. WT mice. Overall, our findings suggest that reduced adaptation and increased oddball processing might contribute to altered perceptual experiences in FX and autism.
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Castellano, Marta. "Computational Principles of Neural Processing: modulating neural systems through temporally structured stimuli." Doctoral thesis, 2014. https://repositorium.ub.uni-osnabrueck.de/handle/urn:nbn:de:gbv:700-2014121112959.
Full textAbstract:
In order to understand how the neural system encodes and processes information, research
has focused on the study of neural representations of simple stimuli, paying
no particular attention to it's temporal structure, with the assumption that a deeper
understanding of how the neural system processes simpli fied stimuli will lead to an understanding of how the brain functions as a whole [1]. However, time is intrinsically bound to neural processing as all sensory, motor, and cognitive processes are inherently dynamic. Despite the importance of neural and stimulus dynamics, little is known of how the neural system represents rich spatio-temporal stimulus, which ultimately link the neural system to a continuously changing environment. The purpose of this thesis is to understand whether and how temporally-structured neural activity modulates the processing of information within the brain, proposing in turn that, the precise interaction
between the spatio-temporal structure of the stimulus and the neural system is
particularly relevant, particularly when considering the ongoing plasticity mechanisms
which allow the neural system to learn from experience. In order to answer these questions, three studies were conducted. First, we studied the impact of spiking temporal structure on a single neuron spiking response, and explored in which way the functional connections to pre-synaptic neurons are modulated through adaptation. Our results suggest that, in a generic spiking neuron, the temporal
structure of pre-synaptic excitatory and inhibitory neurons modulate both the
spiking response of that same neuron and, most importantly, the speed and strength
of learning. In the second, we present a generic model of a spiking neural network that processes rich spatio-temporal stimuli, and explored whether the processing of stimulus within the network is modulated due to the interaction with an external dynamical
system (i.e. extracellular media), as well as several plasticity mechanisms. Our results
indicate that the memory capacity, that re
ects a dynamic short-term memory of incoming stimuli, can be extended on the presence of plasticity and through the interaction with an external dynamical system, while maintaining the network dynamics in a regime suitable for information processing. Finally, we characterized cortical
signals of human subjects (electroencephalography, EEG) associated to a visual categorization task. Among other aspects, we studied whether changes in the dynamics of the stimulus leads to a changes in the neural processing at the cortical level, and introduced the relevance of large-scale integration for cognitive processing. Our results suggest that the dynamic synchronization across distributed cortical areas is stimulus specific and specifically linked to perceptual grouping.
Taken together, the results presented here suggest that the temporal structure of the
stimulus modulates how the neural system encodes and processes information within
single neurons, network of neurons and cortical areas. In particular, the results indicate that timing modulates single neuron connectivity structures, the memory capability of networks of neurons, and the cortical representation of a visual stimuli. While the learning of invariant representations remains as the best framework to account for a number of neural processes (e.g. long-term memory [2]), the reported studies seem to provide support the idea that, at least to some extent, the neural system functions in a non-stationary fashion, where the processing of information is modulated by the stimulus dynamics itself. Altogether, this thesis highlights the relevance of understanding adaptive processes and their interaction with the temporal structure of the stimulus, arguing that a further understanding how the neural system processes dynamic stimuli is crucial for the further understanding of neural processing itself, and any theory that aims to understand neural processing should consider the processing of dynamic signals. 1. Frankish, K., and Ramsey, W. The Cambridge Handbook of Cognitive Science.
Cambridge University Press, 2012. // 2. McGaugh, J. L. Memory{a Century of Consolidation. Science 287, 5451 (Jan. 2000), 248{251.
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Podubnaia-Birca, Ala. "Caractérisation électro-clinique des convulsions fébriles et risque d’épilepsie." Thèse, 2008. http://hdl.handle.net/1866/2775.
Full textAbstract:
Environ 2-3% d’enfants avec convulsions fébriles (CF) développent une épilepsie, mais les outils cliniques existants ne permettent pas d’identifier les enfants susceptibles de développer une épilepsie post-convulsion fébrile. Des études ont mis en évidence des anomalies d’EEG quantifiée, et plus particulièrement en réponse à la stimulation lumineuse intermittente (SLI), chez des patients épileptiques. Aucune étude n’a analysé ces paramètres chez l’enfant avec CF et il importe de déterminer s’ils sont utiles pour évaluer le pronostic des CF.
Les objectifs de ce programme de recherche étaient d’identifier, d’une part, des facteurs de risque cliniques qui déterminent le développement de l’épilepsie après des CF et, d’autre part, des marqueurs électrophysiologiques quantitatifs qui différencieraient les enfants avec CF des témoins et pourraient aider à évaluer leur pronostic.
Afin de répondre à notre premier objectif, nous avons analysé les dossiers de 482 enfants avec CF, âgés de 3 mois à 6 ans. En utilisant des statistiques de survie, nous avons décrit les facteurs de risque pour développer une épilepsie partielle (antécédents prénataux, retard de développement, CF prolongées et focales) et généralisée (antécédents familiaux d’épilepsie, CF récurrentes et après l’âge de 4 ans). De plus, nous avons identifié trois phénotypes cliniques distincts ayant un pronostic différent : (i) CF simples avec des antécédents familiaux de CF et sans risque d’épilepsie ultérieure; (ii) CF récurrentes avec des antécédents familiaux d’épilepsie et un risque d’épilepsie généralisée; (iii) CF focales avec des antécédents familiaux d’épilepsie et un risque d’épilepsie partielle.
Afin de répondre à notre deuxième objectif, nous avons d’abord analysé les potentiels visuels steady-state (PEVSS) évoqués par la SLI (5, 7,5, 10 et 12,5 Hz) en fonction de l’âge. Le tracé EEG de haute densité (128 canaux) a été enregistré chez 61 enfants âgés entre 6 mois et 16 ans et 8 adultes normaux. Nous rapportons un développement topographique différent de l’alignement de phase des composantes des PEVSS de basses (5-15 Hz) et de hautes (30-50 Hz) fréquences. Ainsi, l’alignement de phase des composantes de basses fréquences augmente en fonction de l’âge seulement au niveau des régions occipitale et frontale. Par contre, les composantes de hautes fréquences augmentent au niveau de toutes les régions cérébrales.
Puis, en utilisant cette même méthodologie, nous avons investigué si les enfants avec CF présentent des anomalies des composantes gamma (50-100 Hz) des PEVSS auprès de 12 cas de CF, 5 frères et sœurs des enfants avec CF et 15 témoins entre 6 mois et 3 ans. Nous montrons une augmentation de la magnitude et de l’alignement de phase des composantes gamma des PEVSS chez les enfants avec CF comparés au groupe témoin et à la fratrie.
Ces travaux ont permis d’identifier des phénotypes électro-cliniques d’intérêt qui différencient les enfants avec CF des enfants témoins et de leur fratrie. L’étape suivante sera de vérifier s’il y a une association entre les anomalies retrouvées, la présentation clinique et le pronostic des CF. Cela pourrait éventuellement aider à identifier les enfants à haut risque de développer une épilepsie et permettre l’institution d’un traitement neuroprotecteur précoce.The incidence of epilepsy in children with febrile seizures (FS) varies from 2 to 3%, but available clinical tools do not allow the identification of those children who will later develop epilepsy. Evidences have shown quantitative EEG abnormalities, more particularly revealed by intermittent photic stimulation (IPS), in patients with epilepsy. No studies have yet examined quantitative EEG parameters in children with FS. It is not known either whether they can be relevant to the evaluation of FSs prognosis. The objectives of this research program were to identify, first, clinical risk factors for developing epilepsy after FS and, second, to determine quantitative EEG markers that differentiate FS patients from normal controls and may aid to evaluate their prognosis. In order to meet our first objective, we reviewed the charts of 482 children with FS, aged 3 months to 6 years. Using survival statistics, we described risk factors for developing partial (prenatal antecedents, developmental delay, prolonged and focal FS) and generalized (family history of epilepsy, recurrent FS and FS after the age of 4 years) epilepsy after FS. In addition, we identified several distinct clinical phenotypes related to the prognosis of FS: (i) simple FS with a family history of FS, not related to a subsequent epilepsy, (ii) recurrent FS with a family history of epilepsy and an increased risk of generalised epilepsy and (iii) focal FS with a family history of epilepsy and an increased risk of partial epilepsy. In order to meet our second objective, we analyzed the steady-state visual potentials (SSVEP) evoked by IPS (5, 7.5, 10 and 12.5 Hz) as a function of age. The high density EEG (128 channels) was recorded in 61 normal children between 6 months and 16 years of age and 8 adults. We showed different topographical development of low (5-15 Hz) and high (30-50 Hz) frequency SSVEP components phase alignment. Thus, low frequency phase alignment increased with age only over the frontal and occipital regions, whereas high frequency phase alignment increased over all cerebral regions. Then, using the same methodology, we investigated whether children with FS show abnormalities of gamma frequency SSVEP components. We show an increase of both magnitude and phase alignment of the gamma frequency SSVEP components in 12 FS patients compared to 5 siblings of FS patients and 15 control children between 6 and 36 months of age. This study has identified distinct electro-clinical phenotypes that differentiate FS patients from the group of siblings and controls. Future studies should investigate whether detected abnormalities are associated with the clinical presentation of FS and their prognosis. This could help identify children with FSs who will later develop epilepsy and would eventually allow the institution of an early neuroprotective treatment.
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Wu, Ying-Ting, and 吳熒庭. "If I Were for Real : Visual Works Derived from the Oscillation between Construction and Deconstruction of Self Identity." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/63154079607641203051.
Full textAbstract:
碩士實踐大學
時尚與媒體設計研究所
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If I take off the mask, will the face still be clearly recognizable? I don’t want anyone to see me through, because I’m concealing a truth that is inconvenient to me. The essential part of the thesis was inspired by the struggle between external behaviors and internal emotions as a result of a self-awareness experience during my adolescence. I feel a sense of security as I intend to be invisible and be alienated from interpersonal relations; however, being in great solitude, I gradually cannot distinguish true from fake and begin to negate myself. My secret is concealed and nourished by lies, it sprouts evergreen vines and they tie me up so severely that I could suffocate. “To be happy is to be able to become aware of oneself without fright,” writes Walter Benjamin. I am unable to get rid of my past life experience, but I am willing to transform them into the inexhaustible energy of creating my pieces and hope they could unleash the masks on me. Furthermore, with visual works derived from the concept of stream of consciousness, my past, present and future will ultimately be interweaved to portrait the real me.