Littérature scientifique sur le sujet « Event-related oscillations »
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Articles de revues sur le sujet "Event-related oscillations"
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Yordanova, Juliana, et Vasil Kolev. « Event-Related Brain Oscillations ». Journal of Psychophysiology 23, no 4 (janvier 2009) : 174–82. http://dx.doi.org/10.1027/0269-8803.23.4.174.
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Neuroelectric oscillations provide important tools to study information processing in the brain. In this paper, major concepts and advantages of event-related oscillations (EROs) are considered, with a focus on their relevance for developmental research. Findings from previous studies in passive and oddball conditions are summarized to demonstrate that the age-dependent power decrease of theta (4–7 Hz) and alpha (8–14 Hz) EROs is accompanied by an increase in the synchronization of these oscillations. New data are presented to test whether this dissociation depends on processing demands in a frequency-specific manner. Results from an auditory serial learning task with working memory activation performed by 70 subjects (children from 6 to 10 years of age and adults) indicate that this effect was observed for theta and slow alpha oscillations, whereas an age-dependent decrease in event-related phase synchronization was found for fast alpha oscillations. It is concluded that phase synchronization of only the major theta and alpha EROs may reflect the neurobiological maturation of neural networks involved in perception. Phase synchronization of EROs, however, especially from faster frequency bands, essentially depends on the mode of network involvement and functional competence, which is associated with cognitive processing abilities or strategies in the course of development.
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López-Caneda, Eduardo, Socorro Rodríguez Holguín, Ángeles Correas, Carina Carbia, Alberto González-Villar, Fernando Maestú et Fernando Cadaveira. « Binge drinking affects brain oscillations linked to motor inhibition and execution ». Journal of Psychopharmacology 31, no 7 (7 février 2017) : 873–82. http://dx.doi.org/10.1177/0269881116689258.
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Introduction: Neurofunctional studies have shown that binge drinking patterns of alcohol consumption during adolescence and youth are associated with anomalies in brain functioning. Recent evidence suggests that event-related oscillations may be an appropriate index of neurofunctional damage associated with alcoholism. However, there is no study to date that has evaluated the effects of binge drinking on oscillatory brain responses related to task performance. The purpose of the present study was to examine brain oscillations linked to motor inhibition and execution in young binge drinkers (BDs) compared with age-matched controls. Methods: Electroencephalographic activity was recorded from 64 electrodes while 72 university students (36 controls and 36 BDs) performed a visual Go/NoGo task. Event-related oscillations along with the Go-P3 and NoGo-P3 event-related potential components were analysed. Results: While no significant differences between groups were observed regarding event-related potentials, event-related oscillation analysis showed that BDs displayed a lower oscillatory response than controls in delta and theta frequency ranges during Go and NoGo conditions. Conclusions: Findings are congruent with event-related oscillation studies showing reduced delta and/or theta oscillations in alcoholics during Go/NoGo tasks. Thus, BDs appear to show disruptions in neural oscillations linked to motor inhibition and execution similar to those observed in alcohol-dependent subjects. Finally, these results are the first to evidence that oscillatory brain activity may be a sensitive indicator of underlying brain anomalies in young BDs, which could complement standard event-related potential measures.
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Zhang, Guanghui, Xueyan Li et Fengyu Cong. « Objective Extraction of Evoked Event-Related Oscillation from Time-Frequency Representation of Event-Related Potentials ». Neural Plasticity 2020 (19 décembre 2020) : 1–20. http://dx.doi.org/10.1155/2020/8841354.
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Evoked event-related oscillations (EROs) have been widely used to explore the mechanisms of brain activities for both normal people and neuropsychiatric disease patients. In most previous studies, the calculation of the regions of evoked EROs of interest is commonly based on a predefined time window and a frequency range given by the experimenter, which tends to be subjective. Additionally, evoked EROs sometimes cannot be fully extracted using the conventional time-frequency analysis (TFA) because they may be overlapped with each other or with artifacts in time, frequency, and space domains. To further investigate the related neuronal processes, a novel approach was proposed including three steps: (1) extract the temporal and spatial components of interest simultaneously by temporal principal component analysis (PCA) and Promax rotation and project them to the electrode fields for correcting their variance and polarity indeterminacies, (2) calculate the time-frequency representations (TFRs) of the back-projected components, and (3) compute the regions of evoked EROs of interest on TFRs objectively using the edge detection algorithm. We performed this novel approach, conventional TFA, and TFA-PCA to analyse both the synthetic datasets with different levels of SNR and an actual ERP dataset in a two-factor paradigm of waiting time (short/long) and feedback (loss/gain) separately. Synthetic datasets results indicated that N2-theta and P3-delta oscillations can be stably detected from different SNR-simulated datasets using the proposed approach, but, by comparison, only one oscillation was obtained via the last two approaches. Furthermore, regarding the actual dataset, the statistical results for the proposed approach revealed that P3-delta was sensitive to the waiting time but not for that of the other approaches. This study manifested that the proposed approach could objectively extract evoked EROs of interest, which allows a better understanding of the modulations of the oscillatory responses.
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Ülgen, Zehra, Mert Küçük, Christina Schmiedt-Fehr et Canan Başar-Eroğlu. « Event Related Theta Oscillations During Sustained Attention ». International Journal of Psychophysiology 168 (octobre 2021) : S98—S99. http://dx.doi.org/10.1016/j.ijpsycho.2021.07.298.
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Kolev, Vasil, Juliana Yordanova, Martin Schürmann et Erol Baţar. « Event-related alpha oscillations in task processing ». Clinical Neurophysiology 110, no 10 (octobre 1999) : 1784–92. http://dx.doi.org/10.1016/s1388-2457(99)00105-4.
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Sanchez-Alavez, Manuel, Patricia Robledo, Derek N. Wills, James Havstad et Cindy L. Ehlers. « Cholinergic modulation of event-related oscillations (ERO) ». Brain Research 1559 (avril 2014) : 11–25. http://dx.doi.org/10.1016/j.brainres.2014.02.043.
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Balconi, Michela, et Uberto Pozzoli. « Event-Related Oscillations (ERO) and Event-Related Potentials (ERP) in Emotional Face Recognition ». International Journal of Neuroscience 118, no 10 (janvier 2008) : 1412–24. http://dx.doi.org/10.1080/00207450601047119.
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Heinrich, Hartmut, Vasil Kolev, Aribert Rothenberger et Juliana Yordanova. « Event-Related Oscillations and Cognitive Processes in Children ». Journal of Psychophysiology 23, no 4 (janvier 2009) : 199–207. http://dx.doi.org/10.1027/0269-8803.23.4.199.
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Event-related EEG modulations, which are phase-locked to perceptual, cognitive, and motor processes, are often studied by means of event-related potentials (ERPs), although event-related oscillatory responses in different EEG frequency bands allow a more refined analysis, closer to brain physiology. This article introduces the basics of time-frequency methods, which are typically applied for the analysis of event-related oscillations, focusing on adaptive procedures (e.g., wavelet networks). The potential of these methods is illustrated. Findings about event-related oscillations (gamma responses, theta responses) in children performing an auditory selective attention task are reviewed. Both the neuronal substrates of gamma (30–70 Hz) networks and the ability to synchronize these networks in relation to task-specific processes are available in children and adolescents from 9 to 16 years of age. Developmental changes in the task reactivity of synchronized gamma oscillations may provide evidence for a transition in cognitive processing strategies emerging at the age of 12–13 years. Event-related theta (3–7.5 Hz) activity is enhanced in two latency ranges. The early event-related theta response occurring 0–200 ms after a stimulus may be associated with representations of relevant target features in working memory. The late fronto-central theta response (200 – 450 ms) could be related to the processing of task-irrelevant information. In summary, event-related oscillations can be analyzed using time-frequency methods like wavelet networks. This approach should be used intensively to study neurocognitive development in children.
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Balconi, Michela, et Uberto Pozzoli. « Event-related oscillations (EROs) and event-related potentials (ERPs) comparison in facial expression recognition ». Journal of Neuropsychology 1, no 2 (septembre 2007) : 283–94. http://dx.doi.org/10.1348/174866407x184789.
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Andrew, Colin, et George Fein. « Event-Related Oscillations Versus Event-Related Potentials in a P300 Task as Biomarkers for Alcoholism ». Alcoholism : Clinical and Experimental Research 34, no 4 (avril 2010) : 669–80. http://dx.doi.org/10.1111/j.1530-0277.2009.01136.x.
Texte intégralThèses sur le sujet "Event-related oscillations"
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Doege, Kathrin. « Event-related low-frequency oscillations in schizophrenia ». Thesis, University of Nottingham, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.546270.
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Finke, Mareike. « Brain mechanisms of executive control : Event-related potentials and oscillations in schizophrenic patients and healthy controls during task-switching ». Doctoral thesis, Universitat de Barcelona, 2013. http://hdl.handle.net/10803/98349.
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The brain's ability to represent, maintain and update contextual (task-set) information enables us to alternate successfully between different tasks. Task-set reconfiguration is required when task demands change, as goal directed behaviour has to be adjusted to the new task. Task-cueing paradigms are widely used to investigate the underlying processes which include attentional shifting from one task to the other (task-set shifting), the retrieval of goals and rules as well as the inhibition of the previously relevant (but now irrelevant) task-set.
In the first study, different aspects regarding the extraction of cue information and its importance for task-switching processes were investigated. The main focus of interest were the electrophysiological modulations regarding changes in sensory cues which (1) are or are not related to a switch in task, or even (2) may not carry any task-relevant information in some trials. The process of early (task-relevant) change detection is important in order to prepare the upcoming task. The results suggest that cue-locked event-related potentials (ERPs) are not modulated due to purely sensory changes, but rather any such ERP modulations reflect a task-related process. At least three sub-processes were identified: (1) a fast detection of task-relevant changes (as early as 180 ms), (2) a process of cue-response mapping, and (3) the reloading/updating of stimulus-response mappings. Target-locked analyses revealed that non-informative cue switches do not affect task preparation in any significant way.
The second study consisted of the analysis of the data from study I in the time-frequency domain in order to elucidate power changes in the alpha and theta bands. We independently manipulated (1) anticipatory task preparation by manipulating the informativeness of cues about the upcoming task, and (2) the exogenous contribution to endogenous task-set switching. This design enabled us to examine the relative contribution from exogenous cue changes upon endogenous task-set reconfiguration effects, and whether those effects depend on the presence of foreknowledge about the upcoming task.
The data confirmed strong generic preparation benefits as visible in behavioural performance and both frequency bands. Task switching effects in the alpha band could be related to both goal shifting and rule activation while task switch effects in the theta band seemed related to initial task-set reconfiguration rather than task-set implementation. Strong oscillatory modulations for cue switch trials suggested an “incongruent cue-task transition” effect. Importantly, no significant effects for “task-neutral” cue switches were found.
The third study aimed to investigate higher order cognitive impairments in schizophrenia. Previously, such type of deficits has been conceptualized as failures in executive control and contextual processing. Alternatively, disturbances in high-order cognitive functions might also be due to more delimited deficits, especially in lower-level stages of contextual processing. Moreover, early processing stages do not involve only mere sensory processing, but rather reflect interacting sensory and cognitive mechanisms. Therefore, it was deemed necessary to explore the patients' task-switching abilities by manipulating sensory updating and task-set updating orthogonally to examine the interplay between bottom-up and top-down control processes. Our results suggested that the observed impairments in task-switching behaviour in schizophrenic patients were not specifically related to anticipatory set-shifting, but derived from disrupted early sensory processes of both cue- and target-locked information, as well as from a deficit in the implementation of task-set representations at target onset in the presence of irrelevant and conflicting information.Esta tesis tuvo como objetivo investigar los procesos de cambio de tarea en pacientes esquizofrénicos y controles sanos mediante un paradigma de cambio de tarea con indicadores explícitos. El estudio I examinó el uso de conocimiento previo durante el cambio de tarea, manipulando la actualización sensorial y el control ejecutivo en ensayos con indicadores informativos y no-informativos. Los cambios sensoriales en el estímulo indicador modularon los potenciales evocados (PEs) asociados al indicador sólo cuando contuvieron información conceptual sobre la tarea. La preparación para la tarea facilitó una re-asignación estímulo-respuesta ante el estímulo diana, suscitando respuestas más rápidas en todos los ensayos repetitivos. Los resultados apoyan la hipótesis de una detección rápida de los cambios sensoriales (del indicador) cuando éstos son relevantes para la tarea, y son contrarios a los beneficios por repetición de tarea debidos a una preparación (priming) perceptiva por repetición. El segundo estudio examinó las modulaciones en las oscilaciones neuronales en las bandas alfa y theta de los datos del estudio I. Los resultados también revelaron importantes beneficios en la ejecución conductual. En los ensayos de cambio de tarea durante la actualización y la implementación de la tarea, el ritmo alfa estuvo relacionado con ambos procesos evocados por el indicador sensorial y el estímulo diana, respectivamente. Por el contrario, el ritmo theta estuvo más relacionado con las etapas iniciales de la preparación de tarea. Estos dos estudios refuerzan la hipótesis de que las modulaciones en la actividad cerebral asociadas a un cambio del indicador de tarea no son provocadas por un cambio sensorial simple, sino que están relacionadas con un cambio de meta de orden superior. En el tercer estudio un protocolo de cambio de tarea con indicador explícito fue administrado a un grupo de pacientes esquizofrénicos y comparado con una muestra control sana. Los resultados sugieren que las alteraciones observadas en la conducta de cambio de tarea no estuvieron relacionadas específicamente con una reconfiguración estímulo-respuesta de orden superior, sino a un déficit en la implementación de dicha representación configuracional de la tarea durante la presentación del estímulo diana en presencia de información irrelevante y conflictiva.
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Haig, Albert Roland. « Missing Links the role of phase synchronous gamma oscillations in normal cognition and their dysfunction in schizophrenia ». University of Sydney. Psychological Medicine, 2002. http://hdl.handle.net/2123/848.
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SUMMARY Introduction: There has recently been a great deal of interest in the role of synchronous high-frequency gamma oscillations in brain function. This interest has been motivated by an increasing body of evidence, that oscillations which are synchronous in phase across separated neuronal populations, may represent an important mechanism by which the brain binds or integrates spatially distributed processing activity which is related to the same object. Many models of schizophrenia suggest an impairment in the integration of brain processing, such as a loosening of associations, disconnection, defective multiple constraint organization, or cognitive dysmetria. This has led to recent speculation that abnormalities of high-frequency gamma synchronization may reflect a core dimension of the disturbance underlying this disorder. However, examination of the phase synchronization of gamma oscillations in patients with schizophrenia has never been previously undertaken. Method: In this thesis a new method of analysis of gamma synchrony was introduced, which enables the phase relationships of oscillations in a specific frequency band to be examined across multiple scalp sites as a function of time. This enabled, for the first time, the phase synchronization of gamma oscillations across widespread regions, to be studied in electrical brain activity measured at the scalp in humans. Gamma synchrony responses were studied in electroencephalographic (EEG) data acquired during a commonly employed conventional auditory oddball paradigm. The research consisted of two sets of experiments. In the first set of experiments, data from 100 normal subjects, consisting of 10 males and 10 females in each age decade from 20 to 70, was examined. These experiments were designed to characterize the gamma synchonizations that occurred in response to target and background stimuli and their functional significance in normal brain activity, and to exclude the possibility of these findings being due to electromyogram (EMG) or volume conduction artifact. The examination of functional significance involved the development of an additional new analysis technique. In the second set of experiments, data acquired from 35 patients with schizophrenia and 35 matched normal controls was analyzed. The purpose of these experiments was to determine whether patients showed disturbances of gamma synchrony compared to controls, and to establish the relationship of any such disturbances to medication levels, symptom profiles, duration of illness, and a range of psychophysiological variables. Results: In the 100 normals, responses to target stimuli were characterized by two bursts of synchronous gamma oscillations, an early (evoked) and a late (induced) synchronization, with different topographic distributions. Only the early gamma synchronization was seen in response to background stimuli. The main variable modulating the magnitude of these gamma synchronizations from epoch to epoch was pre-stimulus EEG theta (3-7 Hz) and delta (1-3 Hz) power. Early and late gamma synchrony were also associated with N1 and P3 ERP component amplitude across epochs. Across subjects, the early gamma synchronization was associated with shorter latency of the ERP components P2, N2 and P3, smaller amplitude of N1 and P2, and smaller pre-stimulus beta power. The control analyses showed that these gamma responses were specific to a narrow frequency range (37 to 41 Hz), and were not present in adjacent frequency bands. The responses were not generated by EMG contamination or volume conduction. In the 35 patients with schizophrenia, significant abnormalities of both the early and late synchronizations were observed compared to the 35 normal controls, with distinctive topographic characteristics. In general, early gamma synchrony was increased in patients compared to controls, and late gamma synchrony was decreased. These gamma synchrony disturbances were not related to medication level or the four summed symptom profile scores (positive, negative, general and total). They were, however, associated with duration of illness, becoming less severe the longer the patient had suffered from the disorder. The disordered gamma synchrony in patients was not secondary to abnormalities in other psychophysiological variables, but appeared to represent a primary disturbance. Discussion: The early synchronization may relate to the binding of object representations in early sensory processing, or, given that a constant inter-stimulus interval was employed, may be anticipatory and related to active memory. The late response is probably involved in binding in relation to activation of the internal contextual model involved in late expectancy/contextual processing (context updating or context closure) for target stimuli. The across epochs effects may relate to whether the focus of attention immediately prior to stimulus presentation is internal or is directed at the task. The across subjects effects suggest that a larger magnitude of the early gamma synchronization might indicate that the subject maintains a more stable and less ambiguous internal representation of the environment, that reduces the complexity of input and facilitates target/background discrimination and subsequent processing. The early gamma synchronization findings in patients with schizophrenia suggest that anticipatory processing involving active memory and forward-prediction of the environment is subject to over-binding or the formation of inappropriate associations. The late synchronization disturbances may reflect a fragmentation of contextual processing, and an inability to maintain contextual models of the environment intact over time. Conclusion: This research demonstrates the potential importance of integrative network activity as indexed by gamma phase synchrony in relation to normal cognition, and the possible broad relevance of such activity in psychiatric disorders. In particular, the application in this study to patients with schizophrenia showed that an impairment of brain integrative activity (missing links) might be a key feature of this illness.
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Craddock, Matt, Jasna Martinovic et Matthias M. Müller. « Early and late effects of objecthood and spatial frequency on event-related potentials and gamma band activity ». Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-161492.
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Background: The visual system may process spatial frequency information in a low-to-high, coarse-to-fine sequence. In particular, low and high spatial frequency information may be processed via different pathways during object recognition, with LSF information projected rapidly to frontal areas and HSF processed later in visual ventral areas. In an electroencephalographic study, we examined the time course of information processing for images filtered to contain different ranges of spatial frequencies. Participants viewed either high spatial frequency
(HSF), low spatial frequency (LSF), or unfiltered, broadband (BB) images of objects or nonobject textures, classifying them as showing either man-made or natural objects, or nonobjects. Event-related potentials (ERPs) and evoked and total gamma band activity (eGBA and tGBA) recorded using the electroencephalogram were compared for object and nonobject images across the different spatial frequency ranges. Results: The visual P1 showed independent modulations by object and spatial frequency, while for the N1 these factors interacted. The P1 showed more positive amplitudes for objects than nonobjects, and more positive amplitudes for BB than for HSF images, which in turn evoked more positive amplitudes than LSF images. The peak-to-peak N1 showed that the N1 was much reduced for BB non-objects relative to all other images, while HSF and LSF nonobjects still elicited as negative an N1 as objects. In contrast, eGBA was influenced by spatial
frequency and not objecthood, while tGBA showed a stronger response to objects than nonobjects. Conclusions: Different pathways are involved in the processing of low and high spatial frequencies during
object recognition, as reflected in interactions between objecthood and spatial frequency in the visual N1 component. Total gamma band seems to be related to a late, probably highlevel representational process.
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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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Rodriguez, Rodriguez Andrea del Pilar. « Event-related potentials and pathology in rodent models of Alzheimer's disease and Absence Epilepsy ». Doctoral thesis, 2016. http://hdl.handle.net/11562/939616.
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L'elettroencefalografia (EEG), ed in particolare lo studio dei potenziali e delle oscillazioni correlate ad eventi (ERPs e EROs, dall'inglese event-related potentials, event-related oscillations), costituisce uno strumento ampiamente utilizzato sia in clinica, sia nel campo della ricerca preclinica, dei disordini cerebrali, grazie anche a sui bassi costi e la non invasività. L'attività elettrica cerebrale dell'uomo e dei roditori sono accumunate da diverse caratteristiche; ciò ha reso tali tecniche di particolare interesse anche dal punto di vista traslazionale. In questa tesi di dottorato sono state effettuate registrazioni encefalografiche in topi “wild-type”, in modelli sperimentali di topi transgenici della malattia di Alzheimer, in modelli sperimentali di ratto della epilessia tipo assenza giovanile (absence epilepsy) e in topi spontaneamente affetti da epilessia legata al sonno.1) Lo studio dei potenziali correlati ad eventi sonori (AERPs, dall'inglese auditory event-related potentials) e delle EROs in risposta a diversi tipi di manipolazioni durante un paradigma oddball uditivo passivo in topi C56Bl/6 sani hanno costituito l’oggetto del primo studio presentato nella tesi. Le componenti evocate mostrano lo stesso ordine di polarità descritto in uomo e ratto ma con latenze più brevi, differenza probabilmente determinata dalle diverse dimensioni dell'encefalo. A differenza delle componenti precoci, la componente P3 è risultata sensibile alla probabilità di presentazione dello stimolo; in particolare è stata osservata una riduzione all'aumentare della probabilità di presentazione dello stimolo. Inoltre, le EROs associate alla componente P3 risultano essere simili a quelle umane in termini di evoked power e di phase-locking index (PLI). I dati sperimentali qui presentati indicano, quindi, che la componente P3 nel modello murino presenta caratteristiche simili alla componete P300 umana in termini di elaborazione dello stimolo.2) La seconda parte della tesi è focalizzato sullo studio dei topi TASTPM, un modello sperimentale di roditore della malattia di Alzheimer. In particolare, lo studio delle AERPs, delle EROs, e più in generale dell'EEG, hanno mostrato un incremento nella latenza della componente P3 e una riduzioni nell’ampiezza delle componenti N1, P2, e P3 durante l’elaborazione dello stimolo target. Inoltre, i dati neurofisiologici hanno mostrato un incremento dell’attività delta e theta pre-stimolo associato ad una scarsa sincronizzazione dopo lo stimolo target, indici di un deficit nella connettività tra le regioni frontale e parietali, e uno scarso aumento di potenza theta con lo stimolo target. Inoltre, sono state osservate alterazioni elettroencefalografiche a carico del sonno non-REM, quali l’aumento del potere di theta, alpha e beta. Questi risultati supportano l'ipotesi che nel modello sperimentale di topo transgenico TASTPM della malattia di Alzheimer, EEG, AERPs ed EROs potrebbe essere utilizzato come biomarker in quanto riflettono alterazioni dei circuiti neuronali tipici della malattia.3) Nel terzo studio sperimentale della tesi sono state studiate le interazioni tra la corteccia somatosensoriale e i diversi nuclei del talamo, che costituiscono il sistema cortico-talamo-corticale, nel modello di ratto WAG / Rij mediante potenziali evocati elettrici. I dati dello studio hanno mostrato che i nuclei talamici appartenenti alla rete somatosensoriale e alla rete limbica hanno patterns di risposte evocate intensità-dipendente. In particolare, sono state osservate risposte molto diverse tra la parte rostrale e caudale del nucleo reticolare del talamo. Tali risposte evocate riflettono la diversa interazione della corteccia somatosensoriale ipereccitabile con questi circuiti ed indicano, inoltre, che parte caudale e rostrale del nucleo talamico reticolare possono giocare ruoli diversi nel mantenimento delle scariche di onde durante il sonno.4) Nella quarta parte sperimentale della tesi è stata focalizzata sullo studio della struttura del sonno, e dei ritmi sonno-veglia, e sulla caratterizzazione delle scariche spike-waves (di tipo punta-onda) nel modello di topi AJ/JAX. Le nostre analisi indicano che questo ceppo murino presenta scariche spike-waves ed alterazioni nell'architettura sonno-veglia equivalenti a quelle riportate in pazienti con epilessia di tipo assenza e in modelli genetici di ratto. I risultati dello studio sottolineano, quindi, l'importanza dell’EEG come biomarcatore translazionale nei modelli preclinici.Nel loro complesso, i dati sperimentali qui presentati forniscono informazioni utili alla comprensione delle proprietà dei potenziali evocati nei modelli sperimentali di roditori e sostengono l’ipotesi per cui l'analisi dei segnali EEG posssa costituire uno strumento prezioso sia nello studio dei meccanismi di elaborazione neurosensoriale, sia come biomarker traslazionale nello studio di malattie neurologiche.Electroencephalography (EEG), including the study of event-related potentials (ERPs) and event-related oscillations (EROs), are cost-effective tools in both the clinical practice and in preclinical research field of brain disorders. The electrical activity in the human vs. the rodent’s brain share strong similarities, which make these techniques very attractive from a translational standpoint, but much still needs to be accomplished in order to fully characterize the EEG response as a viable biomarker.We carried out recording experiments in: 1) a wild-type mouse strain; 2) a transgenic mouse regarded as a model of Alzheimer’s disease; 3) a rat model of absence epilepsy; and 4) and inbred mouse spontaneously affected by sleep-related epilepsy. 1) In wild-type C56Bl/6 mice, we tested the sensitivity of auditory event-related potentials (AERPs) and EROs to different manipulations during a passive auditory oddball paradigm. The evoked components showed the same order of polarity described in human and rats, but with shorter latencies, possibly due to the differences in brain size. The P3 component, unlike the earlier components, was sensitive to the probability of stimulus presentation, i.e. it was reduced when the probability of stimulus presentation increased. Also, the EROs associated with the P3 component in mice exhibited similarities with human EROs in terms of evoked power and phase-locking index (PLI). These findings suggest that the P3 component in mice could share features of the human P300, in terms of stimulus processing correlates.2) In TASTPM mice, we analyzed changes in the AERPs, EROs and EEG. An increase in P3 latency and reductions in the amplitudes of N1, P2, and P3 components during target stimulus processing were found in these transgenic mice. Also, these mice exhibited increased delta and theta pre-stimulus activity associated to poor synchronization after the auditory stimulus, connectivity deficits between frontal and parietal sites, and a poor increase of theta total power for the target stimulus. Additionally, specific EEG abnormalities during non-REM sleep characterized by an increase in the power of theta, alpha and beta bands were detected. These findings support the hypothesis that in the TASTPM transgenic model, EEG, AERPs and EROs exhibit anomalies that reflect neural network disturbances typical of AD, and therefore, could be used as biomarkers in transgenic mouse models of AD.3) In WAG/Rij rats, we used electrical evoked potentials to study the interactions between the somatosensorial cortex and different thalamic nuclei, which constitute the cortico-thalamo-cortical system. We detected that the thalamic nuclei that belong to the somatosensorial loop and to the limbic loop have different patterns of electrical evoked responses that are intensity-dependent. In particular, very different responses were detected between the rostral and caudal parts of the thalamic reticular nucleus. These evoked responses reflect the diverse interaction of the hyperexcitable somatosensorial cortex on these circuits and hint the different role of the rostral and caudal parts of the reticular thalamic nucleus in the maintenance of sleep-wave discharges.4) In AJ/JAX mice, we described the sleep-wake architecture and characterized the spike-wave discharges. Our analysis suggest that this strain shows spike-wave discharges and disturbances in the sleep-wake architecture, that are equivalent to the hallmarks reported in patients with absence epilepsy and in genetic rat models. These results highlight the importance of EEG as translatable biomarker in preclinical models. Taken together, these findings strengthen our understanding of the properties of evoked potentials in rodents and support the view that the analysis of EEG signals will prove an invaluable tool, both in the investigation of neurosensory processing mechanisms and as a translational biomarker in studies of neurological diseases.
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Nolden, Sophie. « Activité cérébrale reliée à la rétention des sons en mémoire à court-terme auditive ». Thèse, 2014. http://hdl.handle.net/1866/11150.
Texte intégralRésumé :
Une variété d’opérations cognitives dépend de la capacité de retenir de l’information auditive pour une courte période de temps. Notamment l’information auditive prend son sens avec le temps; la rétention d’un son disparu permet donc de mieux comprendre sa signification dans le contexte auditif et mène ultimement à une interaction réussite avec l’environnement. L’objectif de cette thèse était d’étudier l’activité cérébrale reliée à la rétention des sons et, ce faisant, parvenir à une meilleure compréhension des mécanismes de bas niveau de la mémoire à court-terme auditive.
Trois études empiriques se sont penchées sur différents aspects de la rétention des sons. Le premier article avait pour but d’étudier les corrélats électrophysiologiques de la rétention des sons variant en timbre en utilisant la technique des potentiels reliés aux événements. Une composante fronto-centrale variant avec la charge mnésique a été ainsi révélée. Dans le deuxième article, le patron électro-oscillatoire de la rétention a été exploré. Cette étude a dévoilé une augmentation de l’amplitude variant avec la charge mnésique dans la bande alpha pendant la rétention des sons ainsi qu’une dissociation entre l’activité oscillatoire observée pendant la rétention et celle observée pendant la présentation des sons test. En démontrant des différentes modulations des amplitudes dans la bande alpha et la bande beta, cette étude a pu révéler des processus distincts mais interdépendants de la mémoire à court-terme auditive. Le troisième article a davantage visé à mieux connaître les structures cérébrales soutenant la rétention de sons. L’activité cérébrale a été mesurée avec la magnétoencéphalographie, et des localisations des sources ont été effectuées à partir de ces données. Les résultats ont dévoilé l’implication d’un réseau cérébral contenant des structures temporales, frontales, et pariétales qui était plus important dans l’hémisphère droit que dans l’hémisphère gauche.
Les résultats des études empiriques ont permis de souligner l’aspect sensoriel de la mémoire à court-terme auditive et de montrer des similarités dans la rétention de différentes caractéristiques tonales. Dans leur ensemble, les études ont contribué à l’identification des processus neuronaux reliés à la rétention des sons en étudiant l’activité électromagnétique et l’implication des structures cérébrales correspondantes sur une échelle temporelle fine.The capacity to retain auditory information for a short period of time is fundamental for a variety of cognitive operations. Sounds, in particular, often do not reveal their meaning before being integrated in their temporal context; the retention of tones that are no longer present in the environment is thus necessary for understanding the significance of auditory information. Retaining tones ultimately leads to a successful interaction with the environment. The goal of this thesis was to study brain activity related to the retention of tones, thereby providing a better understanding of low-level mechanisms related to auditory short-term memory. Three empirical studies have been conducted, each of them focusing on a different aspect of the retention of tones. The first article investigated electrophysiological correlates of the retention of tones differing in timbre using the event-related potential technique. The electrophysiological results revealed a fronto-central component that varied with memory load. In the second article, the oscillatory pattern of electric brain activity was explored using electroencephalography. The results revealed that alpha band amplitudes were modulated by memory load during retention. Furthermore, a dissociation of oscillatory activity between the retention of tones and the comparison of test tones against retained tone representations was observed. This study also revealed distinct but interrelated processes taking place at the same time by showing specific amplitude modulations in the alpha and beta bands. The third article focused more on brain areas underpinning the retention of tones. Brain activity was measured with magnetoencephalography and subsequent source localisations were performed. The results suggested the implication of a network of temporal, frontal, and parietal brain areas which was more pronounced in the right hemisphere than in the left hemisphere. The results of the empirical studies emphasized the sensory aspect of auditory short-term memory. In addition, they revealed similarities between the retention of tones differing in fundamental sound characteristics such as timbre and pitch. Considered as a whole, the studies of this thesis contributed to the identification of neural processing underlying the retention of tones by studying electromagnetic brain activity and the implication of corresponding brain areas on a fine temporal scale.
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VECCHIO, ARIANNA. « Modulazione del dolore e dell’empatia per il dolore indotta da analgesia da placebo : personalità e correlati fisiologici ». Doctoral thesis, 2022. http://hdl.handle.net/11573/1632012.
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L’obiettivo di questo lavoro di ricerca è stato lo studio dei sistemi biologico-motivazionali postulati nella Reinforcement Sensitivity Theory (Gray 1970, 1981, 1982; Gray & MacNaughton 2000; MacNaughton & Corr 2004; Corr 2008), e dei correlati fisiologici cerebrali e cardiaci, relati ai processi sensoriali e cognitivi associati all’elaborazione e alla modulazione del dolore, di tipo fisico ed empatico, indotta da placebo. Pertanto, è stata condotta una revisione della letteratura per poi studiare sperimentalmente i fenomeni di interesse. Quindi, nel primo esperimento, è stata valutata l’influenza dei tratti di personalità di approccio ed evitamento sulla modulazione del dolore fasico e dell’empatia per il dolore, indotta da effetto placebo in relazione ai correlati fisiologici associati (potenziali evento-correlati, oscillazioni di frequenza, variabilità interbattito cardiaca), in un campione di 63 partecipanti. I risultati comportamentali hanno evidenziato che il trattamento con placebo ha prodotto una riduzione del dolore e della spiacevolezza percepiti, e dell’empatia per la spiacevolezza altrui. In riferimento allo studio dei correlati elettrocorticali, è stato osservato che il sistema fight-flight-freeze (FFFS) è un moderatore della relazione che intercorre tra i cambiamenti di ampiezza delle componenti P2 e P3 e la riduzione del dolore percepito. In particolare, queste osservazioni sono coerenti con l’idea che bassi punteggi di evitamento attivo (FFFS) predicono la riduzione del dolore indotta dal placebo. Invece, in relazione allo studio delle oscillazioni di frequenza, EEG e cardiaca, evocate dagli stimoli di dolore e di empatia per il dolore durante i trattamenti placebo e controllo, è stato dimostrato che il rallentamento della frequenza cardiaca insieme alla diminuzione della potenza della banda ϑ mediana (4-8 Hz) ha influenzato sia direttamente la riduzione del dolore percepito che indirettamente, attraverso la mediazione del FFFS, e del sistema di inibizione comportamentale. In particolare, nella condizione di empatia per il dolore, è stata osservata un’influenza sia diretta tra la riduzione di potenza per la banda β2 (22-30 Hz) e l’empatia per il dolore altrui, che indiretta, attraverso la mediazione positiva del tratto Total Empathy Ability. In linea con questi risultati, suggeriamo che la modulazione del dolore fasico rispetto al dolore di tipo empatico si basa su processi fisiologici funzionalmente diversi che coinvolgono tratti di personalità differenti.
Infine, nel secondo esperimento abbiamo approfondito lo studio della risposta di empatia per il dolore e la relativa modulazione degli ERP, in un campione di 60 partecipanti. Questo per capire se la risposta empatica sia meglio concettualizzabile in termini di processi cognitivi o come un tratto di personalità. I nostri risultati sostengono la tesi secondo cui durante il processo di identificazione della valenza emotiva di uno stimolo, il contenuto emotivo è in grado di modulare fin dalle prime fasi di elaborazione dello stimolo il riorientamento dell’attenzione e il successivo processo di aggiornamento in memoria associato alla modulazione della risposta empatica (Delplanque, Silvert, Hot, Rigoulot & Sequeira, 2006). A questo proposito, siamo d’accordo con la proposta alternativa di Coll e colleghi (2017), che definisce la risposta empatica in termini di differenze individuali nell’identificazione delle emozioni e nel grado in cui il riconoscimento dello stato emotivo e l’attivazione del proprio sistema provocano una condivisione affettiva nel Sé.The aim of this Ph.D. was the study of biological-motivational systems postulated in the Reinforcement Sensitivity Theory (Gray 1970, 1981, 1982; Gray & MacNaughton 2000; MacNaughton & Corr 2004; Corr 2008) and the physiological cerebral and cardiac correlates, related to the sensory and cognitive processes associated with the modulation of phasic and empathic pain, induced by placebo. Therefore, a literature review was conducted to theoretically study the phenomena of interest that later were investigated experimentally. In the first experiment, we have evaluated the modulation of phasic pain and empathy for pain induced by placebo analgesia to test whether this can reduce both the empathy for pain and the perceived pain by studying the physiological correlates (Evoked Related Potentials components, EEG band power oscillations, and Heart Rate Variability), in a sample of 63 participants. The behavioral results showed that the placebo treatment reduced perceived pain and unpleasantness and empathy unpleasantness. Concerning the study of the ERPs, the results highlighted a moderator effect of the fight-flight-freeze system (FFFS) in the relationships linking P2 and P3 amplitude changes with pain reduction were both significant among low to moderate FFFS values. These observations are consistent with the idea that lower active avoidance (FFFS) scores predict placebo-induced pain reduction. Further, regarding the study of the EEG oscillations and the HRV changes evoked by pain and empathy pain modulation induced by placebo, we found that relative HR-slowing together with decreased midline ϑ-band (4-8 Hz) power directly influenced self-pain reduction and, indirectly, through a mediating effect of the Behavioral Inhibition System and Fight-Flight-Freezing System. In the empathy pain condition, we detected a direct influence of the midline β2-band (22-30 Hz) power reduction on the other-pain decline with a positive mediating role of Total Empathic Ability. In line with these findings, we suggest that the placebo analgesia modulation of first-hand versus other pain relies on different physiological processes involving different personality traits. In this regard, we agree with the alternative proposal by Coll and colleagues (2017), which defines the empathic response in terms of individual differences in two cognitive processes, the identification of emotions, and affective sharing, related to the recognition of the emotional state of the other, in the Self.
Livres sur le sujet "Event-related oscillations"
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Christa, Neuper, et Klimesch Wolfgang, dir. Event-related dynamics of brain oscillations. Amsterdam : Elsevier, 2006.
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Klimesch, Wolfgang, et Christa Neuper. Event-Related Dynamics of Brain Oscillations. Elsevier Science & Technology Books, 2006.
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Pfurtscheller, Gert, et Fernando Lopes da Silva. EEG Event-Related Desynchronization and Event-Related Synchronization. Sous la direction de Donald L. Schomer et Fernando H. Lopes da Silva. Oxford University Press, 2017. http://dx.doi.org/10.1093/med/9780190228484.003.0040.
Texte intégralRésumé :
Event-related desynchronization (ERD) reflects a decrease of oscillatory activity related to internally or externally paced events. The increase of rhythmic activity is called event-related synchronization (ERS). They represent dynamical states of thalamocortical networks associated with cortical information-processing changes. This chapter discusses differences between ERD/ERS and evoked response potentials and methodologies for quantifying ERD/ERS and selecting frequency bands. It covers the interpretation of ERD/ERS in the alpha and beta bands and theta ERS and alpha ERD in behavioral tasks. ERD/ERS in scalp and subdural recordings, in various frequency bands, is discussed. Also presented is the modulation of alpha and beta rhythms by 0.1-Hz oscillations in the resting state and phase-coupling of the latter with slow changes of prefrontal hemodynamic signals (HbO2), blood pressure oscillations, and heart rate interval variations in the resting state and in relation to behavioral motor tasks. Potential uses of ERD-based strategies in stroke patients are discussed.
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(Editor), Christa Neuper, et Wolfgang Klimesch (Editor), dir. Event-Related Dynamics of Brain Oscillations, Volume 159 (Progress in Brain Research). Elsevier Science, 2006.
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Lopes da Silva, Fernando H., et Eric Halgren. Neurocognitive Processes. Sous la direction de Donald L. Schomer et Fernando H. Lopes da Silva. Oxford University Press, 2017. http://dx.doi.org/10.1093/med/9780190228484.003.0048.
Texte intégralRésumé :
Transmembrane neuronal currents that embody cognition in the cortex produce magnetoencephalographic and electroencephalographic signals. Frequency-domain analysis reveals standard rhythms with consistent topography, frequency, and cognitive correlates. Time-domain analysis reveals average event-related potentials and field (ERP/ERF) components with consistent topography, latency, and cognitive correlates. Standard rhythms and ERP/ERF components underlie perceiving stimuli; evaluating whether stimuli match predictions, and taking appropriate action when they do not; encoding stimuli to permit semantic processing and then accessing lexical representations and assigning syntactic roles; maintaining information in primary memory; preparing to take an action; and closing processing of an event–response sequence. Sustained mental processes are associated with theta and gamma. Consolidating memories appears to occur mainly during replay of specific firing patterns during sleep spindles and slow oscillations. Biophysical, neuroanatomical, and neurophysiological factors interact to render cognitive rhythms and components particularly sensitive to the large-scale modulatory processes that sequence and integrate higher cortical processing.
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Brandeis, Daniel, Sandra K. Loo, Grainne McLoughlin, Hartmut Heinrich et Tobias Banaschewski. Neurophysiology. Oxford University Press, 2018. http://dx.doi.org/10.1093/med/9780198739258.003.0009.
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Neurophysiology allows us to understand and modulate the neural mechanisms in ADHD with high time- and/or frequency-resolution. These non-invasive methods include electroencephalographic recordings at rest and during tasks, with spontaneous and event-related oscillations and potentials tracking covert processing and transcranial neuromodulation through magnetic or electric fields. The findings indicate consistent cognitive and neural deficits in ADHD related to impaired attention and deficient inhibition. Advanced signal processing and source imaging methods often converge with other imaging approaches. Neurophysiological findings also reveal considerable heterogeneity in ADHD regarding cognitive, affective, and genetic subtypes. This illustrates the importance of dimensional approaches and of pathophysiological mechanisms partly shared with other disorders. Although several potential neurophysiological markers of ADHD have been considered, a clinical use for individual diagnostics and classification is not supported to date. More research should clarify the clinical potential of multivariate multimodal classification and prediction of treatment outcome to advance individualized treatment.
Chapitres de livres sur le sujet "Event-related oscillations"
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Kaufman, Lloyd. « Cognition and Local Changes in Brain Oscillations ». Dans Oscillatory Event-Related Brain Dynamics, 401–14. Boston, MA : Springer US, 1994. http://dx.doi.org/10.1007/978-1-4899-1307-4_29.
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Başar, Erol. « Event-Related Oscillations in Brain Function ». Dans Springer Series in Synergetics, 417–26. Berlin, Heidelberg : Springer Berlin Heidelberg, 1999. http://dx.doi.org/10.1007/978-3-642-59893-7_31.
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Başar, E., et S. Karakaş. « Event-Related Oscillations in the Brain ». Dans Springer Series in Synergetics, 147–51. Berlin, Heidelberg : Springer Berlin Heidelberg, 1998. http://dx.doi.org/10.1007/978-3-642-72192-2_9.
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Bullock, Theodore H., et Jerzy Z. Achimowicz. « A Comparative Survey of Event Related Brain Oscillations ». Dans Oscillatory Event-Related Brain Dynamics, 11–26. Boston, MA : Springer US, 1994. http://dx.doi.org/10.1007/978-1-4899-1307-4_3.
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Altrup, Ulrich, Michael Madeja, Martin Wiemann et Erwin-Josef Speckmann. « Physiologic and Epileptic Oscillations in a Small Invertebrate Network ». Dans Oscillatory Event-Related Brain Dynamics, 27–42. Boston, MA : Springer US, 1994. http://dx.doi.org/10.1007/978-1-4899-1307-4_4.
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Murthy, Venkatesh N., Fumi Aoki et Eberhard E. Fetz. « Synchronous Oscillations in Sensorimotor Cortex of Awake Monkeys and Humans ». Dans Oscillatory Event-Related Brain Dynamics, 343–56. Boston, MA : Springer US, 1994. http://dx.doi.org/10.1007/978-1-4899-1307-4_24.
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Roelfsema, Pieter R., Andreas K. Engel, Peter König et Wolf Singer. « Oscillations and Synchrony in the Visual Cortex : Evidence for Their Functional Relevance ». Dans Oscillatory Event-Related Brain Dynamics, 99–114. Boston, MA : Springer US, 1994. http://dx.doi.org/10.1007/978-1-4899-1307-4_9.
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Pfurtscheller, Gert. « Event-Related Desynchronization (ERD) and 40-Hz Oscillations in a Simple Movement Task ». Dans Oscillatory Event-Related Brain Dynamics, 357–66. Boston, MA : Springer US, 1994. http://dx.doi.org/10.1007/978-1-4899-1307-4_25.
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Başar, Erol. « Memory Templates in Event-Related Oscillations, P300, MMN ». Dans Springer Series in Synergetics, 207–28. Berlin, Heidelberg : Springer Berlin Heidelberg, 1999. http://dx.doi.org/10.1007/978-3-642-59893-7_16.
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Başar, Erol. « EEG and Event-Related Oscillations as Brain Alphabet ». Dans Springer Series in Synergetics, 407–15. Berlin, Heidelberg : Springer Berlin Heidelberg, 1999. http://dx.doi.org/10.1007/978-3-642-59893-7_30.
Texte intégralActes de conférences sur le sujet "Event-related oscillations"
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QUIAN QUIROGA, R., E. BAŞAR et M. SCHÜRMANN. « PHASE-LOCKING OF EVENT-RELATED ALPHA OSCILLATIONS ». Dans Proceedings of the Workshop. WORLD SCIENTIFIC, 2000. http://dx.doi.org/10.1142/9789812793782_0037.
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Begum, T., F. Reza, A. L. Ahmed, S. Elaina et J. M. Abdullah. « Analysis of event-related alpha oscillations in auditory P300 by Wavelet Transform (WT) method ». Dans 2011 11th International Conference on Hybrid Intelligent Systems (HIS 2011). IEEE, 2011. http://dx.doi.org/10.1109/his.2011.6122098.
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Fu, Yunfa, Baolei Xu, Lili Pei et Hongyi Li. « Phase-Locked and Non-Phase-Locked Event-Related Oscillations and Channel Power Spectra Analysis during Motor Imagery with Speed Parameters for BCRI ». Dans 2011 5th International Conference on Bioinformatics and Biomedical Engineering (iCBBE). IEEE, 2011. http://dx.doi.org/10.1109/icbbe.2011.5780182.
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Castillo-Dura´n, Rogelio, Javier Ortiz-Villafuerte, Raymundo Go´mez-Herrera et Gabriel Calleros-Micheland. « Autoregressive Multivariate Analysis of BWR Bistable Flow ». Dans 16th International Conference on Nuclear Engineering. ASMEDC, 2008. http://dx.doi.org/10.1115/icone16-48730.
Texte intégralRésumé :
Bi-stable flow patterns can induce flow oscillations possibly leading to power fluctuations. In other cases, bi-stable flow can generate loads on components, so that structural stresses may become a potential cause of failure. This type of flow occurs in BWRs at different operation conditions, so there is no an absolute methodology for detection and prediction of such phenomenon. In this work, a multivariate autoregressive (MAR) analysis is performed to different signals related to a bi-stable flow event that occurred in one of the BWR Units at the Laguna Verde Nuclear Power Plant. The signal analysis was performed with the home-developed NOISE computer program, which, among several other applications, computes the autoregressive coefficients which contain the information of the dynamics of the signal, and that later are used to determine the relative power contribution (RPC) ratio, which in turn allows establishing the influence of the different signals on each other. From the signal analysis, among the important results obtained, it was found that no new frequencies appeared during the event. Also, it was determined through the Relative Power Contribution ratios that the most probable cause of reactor power change was the flow variation in the recirculation flow of loop B. Maximum variations (both above and below) from the initial average reactor power were 0.5%, so the bi-stable flow impact was of no safety concern.
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Mantelli, L., M. L. Ferrari et A. Traverso. « Surge Prevention Techniques for a Turbocharged Solid Oxide Fuel Cell Hybrid System ». Dans ASME Turbo Expo 2021 : Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2021. http://dx.doi.org/10.1115/gt2021-59264.
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Abstract Pressurized solid oxide fuel cell (SOFC) systems are one of the most promising technologies to achieve high energy conversion efficiencies and reduce pollutant emissions. The most common solution for pressurization is the integration with a micro gas turbine, a device capable of exploiting the residual energy of the exhaust gas to compress the fuel cell air intake and, at the same time, generating additional electrical power. The focus of this study is on an alternative layout, based on an automotive turbocharger, which has been more recently considered by the research community to improve cost effectiveness at small size (< 100 kW), despite reducing slightly the top achievable performance. Such turbocharged SOFC system poses two main challenges. On one side, the absence of an electrical generator does not allow the direct control of the rotational speed, which is determined by the power balance between turbine and compressor. On the other side, the presence of a large volume between compressor and turbine, due to the fuel cell stack, alters the dynamic behavior of the turbocharger during transients, increasing the risk of compressor surge. The pressure oscillations associated with such event are particularly detrimental for the system, because they could easily damage the materials of the fuel cells. The aim of this paper is to investigate different techniques to drive the operative point of the compressor far from the surge condition when needed, reducing the risks related to transients and increasing its reliability. By means of a system dynamic model, developed using the TRANSEO simulation tool by TPG, the effect of different anti-surge solutions is simulated: (i) intake air conditioning, (ii) water spray at compressor inlet, (iii) air bleed and recirculation, and (iv) installation of an ejector at the compressor intake. The pressurized fuel cell system is simulated with two different control strategies, i.e. constant fuel mass flow and constant turbine inlet temperature. Different solutions are evaluated based on surge margin behavior, both in the short and long terms, but also monitoring other relevant physical quantities of the system, such as compressor pressure ratio and turbocharger rotational speed.
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Gad-el-Hak, Ibrahim, Njuki Mureithi, Kostas Karazis et Gary Williams. « Experimental Investigation of Jet Cross-Flow Induced Vibration of a Rod Bundle ». Dans ASME 2021 Pressure Vessels & Piping Conference. American Society of Mechanical Engineers, 2021. http://dx.doi.org/10.1115/pvp2021-65000.
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Abstract Flow-induced vibration (FIV) is a constant concern in nuclear power plants. Demand for better thermal performance challenges the mechanical and flow characteristics of fuel designs. In the hypothetical case of a loss of coolant (LOCA) event in a reactor, the hydrodynamic pressure would increase significantly across the baffle plates. PWRs include safety features such as Loss-of-Coolant-Accident (LOCA) holes and slots in the core periphery baffles surrounding the fuel assemblies to release the pressure build up during a LOCA event. Accordingly, these fuel assemblies are subjected to combined axial and jet cross-flow at certain axial locations along their spans due to their proximity to the LOCA holes. The jet flow could induce vibrations for fuel assemblies located near LOCA holes, which might lead to grid-to-rod fretting and thus potential fuel failure. Research on circular jet induced vibrations of rod bundles is limited. Thus, it is required to investigate the dynamical behavior of rod bundle subjected to jet flow to define the critical velocity at which the fuel rods may undergo instability. This article presents an experimental study of jet flow induced vibrations for a 6 × 6 closely packed normal square rod bundle with a pitch-to-diameter ratio of 1.32 simulating the actual PWR fuel rod dimensions. A specialized test apparatus was designed to investigate the stability effect of jet centerline offset from array centerline (jet eccentricity). From the test results the instability threshold of the rod bundle subjected to jet cross-flow is determined. The results show that the rod array vibration is affected by the jet eccentricity. Two excitation mechanisms are identified. The first is an apparent lock-in type mechanism that maybe related to shear layer or jet oscillation. The second, more important excitation, is an apparent fluidelastic instability induced by the jet flow.
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Muñoz, David. « New strategies in proprioception’s analysis for newer theories about sensorimotor control ». Dans Systems & Design 2017. Valencia : Universitat Politècnica València, 2017. http://dx.doi.org/10.4995/sd2017.2017.6903.
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Abstract Human’s motion and its mechanisms had become interesting in the last years, where the medecine’s field search for rehabilitation methods for handicapped persons. Other fields, like sport sciences, professional or military world, search to distinguish profiles and ways to train them with specific purposes. Besides, recent findings in neuroscience try to describe these mechanisms from an organic point of view. Until now, different researchs had given a model about control motor that describes how the union between the senses’s information allows adaptable movements. One of this sense is the proprioception, the sense which has a quite big factor in the orientation and position of the body, its members and joints. For this reason, research for new strategies to explore proprioception and improve the theories of human motion could be done by three different vias. At first, the sense is analysed in a case-study where three groups of persons are compared in a controlled enviroment with three experimental tasks. The subjects belong to each group by the kind of sport they do: sedentary, normal sportsmen (e.g. athletics, swimming) and martial sportmen (e.g. karate, judo). They are compared thinking about the following hypothesis: “Martial Sportmen have a better proprioception than of the other groups’s subjects: It could be due to the type of exercises they do in their sports as empirically, a contact sportsman shows significantly superior motor skills to the members of the other two groups. The second via are records from encephalogram (EEG) while the experimental tasks are doing. These records are analised a posteriori with a set of processing algorithms to extract characteristics about brain’s activity of the proprioception and motion control. Finally , the study tries to integrate graphic tools to make easy to understand final scientific results which allow us to explore the brain activity of the subjects through easy interfaces (e.g. space-time events, activity intensity, connectivity, specific neural netwoks or anormal activity). In the future, this application could be a complement to assist doctors, researchers, sports center specialists and anyone who must improve the health and movements of handicapped persons. Keywords: proprioception, EEG, assesment, rehabilitation.References: Röijezon, U., Clark, N.C., Treleaven, J. (2015). Proprioception in musculoskeletal rehabilitation. Part 1: Basic science and principles of assessment and clinical interventions. ManualTher.10.1016/j.math.2015.01.008. Röijezon, U., Clark, N.C., Treleaven, J. (2015). Proprioception in musculoskeletal rehabilitation. Part 2: Clinical assessment and intervention. Manual Ther.10.1016/j.math.2015.01.009. 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