A Generalized Framework for Quantifying the Dynamics of EEG Event-Related Desynchronization

Brains were built by evolution to react swiftly to environmental challenges. Thus, sensory stimuli must be processed ad hoc, i.e., independent—to a large extent—from the momentary brain state incidentally prevailing during stimulus occurrence. Accordingly, computational neuroscience strives to model the robust processing of stimuli in the presence of dynamical cortical states. A pivotal feature of ongoing brain activity is the regional predominance of EEG eigenrhythms, such as the occipital alpha or the pericentral mu rhythm, both peaking spectrally at 10 Hz. Here, we establish a novel generalized concept to measure event-related desynchronization (ERD), which allows one to model neural oscillatory dynamics also in the presence of dynamical cortical states. Specifically, we demonstrate that a somatosensory stimulus causes a stereotypic sequence of first an ERD and then an ensuing amplitude overshoot (event-related synchronization), which at a dynamical cortical state becomes evident only if the natural relaxation dynamics of unperturbed EEG rhythms is utilized as reference dynamics. Moreover, this computational approach also encompasses the more general notion of a “conditional ERD,” through which candidate explanatory variables can be scrutinized with regard to their possible impact on a particular oscillatory dynamics under study. Thus, the generalized ERD represents a powerful novel analysis tool for extending our understanding of inter-trial variability of evoked responses and therefore the robust processing of environmental stimuli

Neurophysiological evaluation of undergraduate portuguese young adults with regarding difficulties

Reading is a complex cognitive process that requires a simultaneous activation of different brain systems. Power EEG has been used to study activation patterns in dyslexic subjects, but so far, studies lack result’s coherence, including in adult dyslexic population. The Reading Age Test (TIL) is a screening assessment for dyslexia. TIL evaluates the processes of decoding and understanding. This test is adapted and validated to Portuguese language. Objective: To analyze neurophysiological differences in undergraduate adults with and without reading difficulties using power EEG, and compare the results with the ones found at younger ages. Methods: 209 college students were administered the TIL. EEG was collected with 26 students (21 within normal reading level; 5 with severe reading difficulties signalized with TIL). During the EEG, the participant was asked to follow a sequence of tasks, during a total of 15 minutes (Basal resting state, TIL, Pos-TIL resting state, Non-reading Task; final resting state). Subsequently, the Fourier Transform (FFT) algorithm was applied to the EEG signal from the Basal resting state and the two given tasks. Power spectra mean values of delta, theta and beta activity band, from electrodes F7, F8, T3, T4, T5 and T6 were analyzed performing Shapiro-Wilk tests. Results: No significant differences in mean variations (sig >0.05) were observed between groups during the analyzed periods, regarding electrode and brain activity band frequency. Conclusion: This study provided inconclusive results concerning power EEG different findings at the lower frontal gyrus region and temporal region, between subject with and without reading difficulties.info:eu-repo/semantics/publishedVersio

Discriminación de estados mentales mediante la extracción de patrones espaciales bajo restricciones de no estacionariedad e independencia de sujeto

graficas, tablasEvaluation of brain dynamics elicited by motor imagery (MI) tasks can contribute to clinical and learning applications. In this work, we propose four specific improvements for brain motor intention response analysis based on EEG recordings by considering the nonstationarity, nonlinearity of brain signals, inter- and intra-subject variability, aimed to provide physiological interpretability and the distintiveness between subjects neural response. Firstly, to build up the subject-level feature framework, a common representational space, is proposed that encodes the electrode (spatial) contribution, evolving through time and frequency domains. Three feature extraction methods were compared, providing insight into the possible limitations. Secondly, we present an Entropy-based method, termed \textit{VQEnt}, for estimation of ERD/S using quantized stochastic patterns as a symbolic space, aiming to improve their discriminability and physiological interpretability. The proposed method builds the probabilistic priors by assessing the Gaussian similarity between the input measured data and their reduced vector-quantized representation. The validating results of a bi-class imagine task database (left and right hand) prove that \textit{VQEnt} holds symbols that encode several neighboring samples, providing similar or even better accuracy than the other baseline sample-based algorithms of Entropy estimation. Besides, the performed ERD/S time-series are close enough to the trajectories extracted by the variational percentage of EEG signal power and fulfill the physiological MI paradigm. In BCI literate individuals, the \textit{VQEnt} estimator presents the most accurate outcomes at a lower amount of electrodes placed in the sensorimotor cortex so that reduced channel set directly involved with the MI paradigm is enough to discriminate between tasks, providing an accuracy similar to the performed by the whole electrode set. Thirdly, multi-subject analysis is to make inferences on the group/population level about the properties of MI brain activity. However, intrinsic neurophysiological variability of neural dynamics poses a challenge for devising efficient MI systems. Here, we develop a \textit{time-frequency} model for estimating the spatial relevance of common neural activity across subjects employing an introduced statistical thresholding rule. In deriving multi-subject spatial maps, we present a comparative analysis of three feature extraction methods: \textit{Common Spatial Patterns}, \textit{Functional Connectivity}, and \textit{Event-Related De/Synchronization}. In terms of interpretability, we evaluate the effectiveness in gathering MI data from collective populations by introducing two assumptions: \textit{i}) Non-linear assessment of the similarity between multi-subject data originating the subject-level dynamics; \textit{ii}) Assessment of time-varying brain network responses according to the ranking of individual accuracy performed in distinguishing distinct motor imagery tasks (left-hand versus right-hand). The obtained validation results indicate that the estimated collective dynamics differently reflect the flow of sensorimotor cortex activation, providing new insights into the evolution of MI responses. Lastly, we develop a data-driven estimator, termed {Deep Regression Network} (DRN), which jointly extracts and performs the regression analysis in order to assess the efficiency of the individual brain networks in practicing MI tasks. The proposed double-stage estimator initially learns a pool of deep patterns, extracted from the input data, in order to feed a neural regression model, allowing for infering the distinctiveness between subject assemblies having similar variability. The results, which were obtained on real-world MI data, prove that the DRN estimator fosters pre-training neural desynchronization and initial training synchronization to predict the bi-class accuracy response, thus providing a better understanding of the Brain--Computer Interface inefficiency of subjects. (Texto tomado de la fuente)La evaluación de la dinámica cerebral provocada por las tareas de imaginación motora (\textit{Motor Imagery - MI}) puede contribuir al desarrollo de aplicaciones clínicas y de aprendizaje. En este trabajo, se proponen cuatro mejoras específicas para el an\'lisis de la respuesta de la intención motora cerebral basada en registros de Electroencefalografía (EEG) al considerar la no estacionariedad, la no linealidad de las se\tilde{n}ales cerebrales y la variabilidad inter e intrasujeto, con el objetivo de proporcionar interpretabilidad fisiológica y la discriminación entre la respuesta neuronal de los sujetos. En primer lugar, para construir el marco de características a nivel de sujeto, se propone un espacio de representación común que codifica la contribución del electrodo (espacial) y como esta evoluciona a través de los dominios de tiempo y frecuencia. Tres métodos de extracción de características fueron comparados, proporcionando información sobre las posibles limitaciones. En segundo lugar, se presenta un método basado en Entropía, denominado \textit{VQEnt}, para la estimación de la desincronización relacionada a eventos (\textit{Event-Related De-Synchronization - ERD/S}) utilizando patrones estocásticos cuantificados en un espacio simbólico, con el objetivo de mejorar su discriminabilidad e interpretabilidad fisiol\'gica. El método propuesto construye los antecedentes probabilísticos mediante la evaluación de la similitud gaussiana entre los datos medidos de entrada y su representación cuantificada vectorial reducida. Los resultados de validación en una base de datos de tareas de imaginación bi-clase (mano izquierda y mano derecha) prueban que \textit{VQEnt} contiene símbolos que codifican varias muestras vecinas, proporcionando una precisión similar o incluso mejor que los otros algoritmos basados en estimación de entropía de referencia. Además, las series temporales de ERD/S calculadas son lo suficientemente cercanas a las trayectorias extraídas por el porcentaje de variación de la potencia de la señal EEG y cumplen con el paradigma fisiológico de MI. En individuos alfabetizados en BCI, el estimador \textit{VQEnt} presenta los resultados precisos con una menor cantidad de electrodos colocados en la corteza sensoriomotora, de modo que el conjunto reducido de canales directamente involucrados con el paradigma MI es suficiente para discriminar entre tareas. En tercer lugar, el análisis multisujeto consiste en hacer inferencias a nivel de grupo/población sobre las propiedades de la actividad cerebral de la imaginación motora. Sin embargo, la variabilidad neurofisiológica intrínseca de la dinámica neuronal plantea un desafío para el diseño de sistemas MI eficientes. En este sentido, se presenta un modelo de \textit{tiempo-frecuencia} para estimar la relevancia espacial de la actividad neuronal común entre sujetos empleando una regla de umbral estadística que deriva en mapas espaciales de múltiples sujetos. Se presenta un análisis comparativo de tres métodos de extracción de características: \textit{Patrones espaciales comunes}, \textit{Conectividad funcional} y \textit{De-sincronización relacionada con eventos}. En términos de interpretabilidad, evaluamos la efectividad en la recopilación de datos de MI para multisujetos mediante la introducción de dos suposiciones: \textit{i}) Evaluación no lineal de la similitud entre los datos de múltiples sujetos que originan la dinámica a nivel de sujeto; \textit{ii}) Evaluación de las respuestas de la red cerebral que varían en el tiempo de acuerdo con la clasificación de la precisión individual realizada al distinguir distintas tareas de imaginación motora (mano izquierda versus mano derecha). Los resultados de validación obtenidos indican que la dinámica colectiva estimada refleja de manera diferente el flujo de activación de la corteza sensoriomotora, lo que proporciona nuevos conocimientos sobre la evolución de las respuestas de MI. Por último, se muestra un estimador denominado {Red de regresión profunda} (\textit{Deep Regression Network - DRN}), que extrae y realiza conjuntamente un análisis de regresión para evaluar la eficiencia de las redes cerebrales individuales, de cada sujeto, en la práctica de tareas de MI. El estimador de doble etapa propuesto inicialmente aprende un conjunto de patrones profundos, extraídos de los datos de entrada, para alimentar un modelo de regresión neuronal, lo que permite inferir la distinción entre conjuntos de sujetos que tienen una variabilidad similar. Los resultados, que se obtuvieron con datos MI del mundo real, demuestran que el estimador DRN usa la desincronización neuronal previa al entrenamiento y la sincronización del entrenamiento inicial para predecir la respuesta de precisión bi-clase, proporcionando así una mejor comprensión de la ineficiencia de la respuesta de MI de los sujetos en las Interfaces Cerebro-Computador.DoctoradoDoctor en IngenieríaReconocimiento de PatronesEléctrica, Electrónica, Automatización Y Telecomunicaciones.Sede Manizale

Assessing the depth of cognitive processing as the basis for potential user-state adaptation

Objective: Decoding neurocognitive processes on a single-trial basis with Brain-Computer Interface (BCI) techniques can reveal the user's internal interpretation of the current situation. Such information can potentially be exploited to make devices and interfaces more user aware. In this line of research, we took a further step by studying neural correlates of different levels of cognitive processes and developing a method that allows to quantify how deeply presented information is processed in the brain. Methods/Approach: Seventeen participants took part in an EEG study in which we evaluated different levels of cognitive processing (no processing, shallow, and deep processing) within three distinct domains (memory, language, and visual imagination). Our investigations showed gradual differences in the amplitudes of event-related potentials (ERPs) and in the extend and duration of event-related desynchronization (ERD) which both correlate with task difficulty. We performed multi-modal classification to map the measured correlates of neurocognitive processing to the corresponding level of processing. Results: Successful classification of the neural components was achieved, which reflects the level of cognitive processing performed by the participants. The results show performances above chance level for each participant and a mean performance of 70–90% for all conditions and classification pairs. Significance: The successful estimation of the level of cognition on a single-trial basis supports the feasibility of user-state adaptation based on ongoing neural activity. There is a variety of potential use cases such as: a user-friendly adaptive design of an interface or the development of assistance systems in safety critical workplaces.DFG, 325093850, Open Access Publizieren 2017 - 2018 / Technische Universität Berli

Causal Shannon-Fisher Characterization of Motor/Imagery Movements in EEG

The electroencephalogram (EEG) is an electrophysiological monitoring method that allows us to glimpse the electrical activity of the brain. Neural oscillations patterns are perhaps the best salient feature of EEG as they are rhythmic activities of the brain that can be generated by interactions across neurons. Large-scale oscillations can be measured by EEG as the different oscillation patterns reflected within the different frequency bands, and can provide us with new insights into brain functions. In order to understand how information about the rhythmic activity of the brain during visuomotor/imagined cognitive tasks is encoded in the brain we precisely quantify the different features of the oscillatory patterns considering the Shannon-Fisher plane H × F. This allows us to distinguish the dynamics of rhythmic activities of the brain showing that the Beta band facilitate information transmission during visuomotor/imagined tasks.Facultad de Ciencias ExactasInstituto de Física de Líquidos y Sistemas Biológico

Induced brain activity as indicator of cognitive processes: experimental-methodical analyses and algorithms for online-applications

Die Signalverarbeitung von elektroenzephalographischen (EEG) Signalen ist ein entscheidendes Werkzeug, um die kognitiven Prozessen verstehen zu können. Beispielweise wird induzierte Hirnaktivität in mehreren Untersuchungen mit kognitiver Leistung assoziiert. Deshalb ist die Gewinnung von elektrophysiologischen Parametern grundlegend für die Charakterisierung von kognitiven Prozessen sowie von kognitiven Dysfunktionen in neurologischen Erkrankungen. Besonders bei Epilepsie treten häufig Störungen wie Gedächtnis-, oder Aufmerksamkeitsprobleme auf, zusätzlich zu Anfällen. Neurofeedback (bzw. EEG-Biofeedback) ist eine Therapiemethode, die zusätzlich zu medikamentösen- und chirurgischen Therapien bei der Behandlung vieler neurologischer Krankheiten, einschließlich Epilepsie, erfolgreich praktiziert wird. Neurofeedback wird jedoch meist dafür angewendet, eine Anfallsreduzierung zu erzielen. Dagegen wird eine Verbesserung kognitiver Fähigkeiten auf der Basis elektrophysiologischer Änderungen selten vorgesehen. Darüber hinaus sind die aktuellen Neurofeedbackstrategien für diesen Zweck ungeeignet. Der Grund dafür sind unter anderem nicht adäquate Verfahren für die Gewinnung und Quantifizierung induzierter Hirnaktivität. Unter Berücksichtigung der oben genannten Punkten wurden die kognitiven Leistungen von einer Patientengruppe (Epilepsie) und einer Probandengruppe anhand der ereignisbezogenen De-/Synchronisation (ERD/ERS) Methode untersucht. Signifikante Unterschiede wurden im Theta bzw. Alpha Band festgestellt. Diese Ergebnisse unterstützen die Verwertung von auf ERD/ERS basierten kognitiven Parametern bei Epilepsie. Anhand einer methodischen Untersuchung von dynamischen Eigenschaften wurde ein onlinefähiger ERD/ERS Algorithmus für zukünftige Neurofeedback Applikationen ausgewählt. Basierend auf dem ausgewählten Parameter wurde eine Methodik für die online Gewinnung und Quantifizierung von kognitionsbezogener induzierter Hirnaktivität entwickelt. Die dazugehörigen Prozeduren sind in Module organisiert, um die Prozessapplikabilität zu erhöhen. Mehrere Bestandteile der Methodik, einschließlich der Rolle von Elektrodenmontagen sowie die Eliminierung bzw. Reduktion der evozierten Aktivität, wurden anhand kognitiver Aufgaben evaluiert und optimiert. Die Entwicklung einer geeigneten Neurofeedback Strategie sowie die Bestätigung der psychophysiologischen Hypothese anhand einer Pilotstudie sollen Gegenstand der zukünftigen Arbeitschritte sein.Processing of electroencephalographic (EEG) signals is a key step towards understanding cognitive brain processes. Particularly, there is growing evidence that the analysis of induced brain oscillations is a powerful tool to analyze cognitive performance. Thus, the extraction of electrophysiological features characterizing not only cognitive processes but also cognitive dysfunctions by neurological diseases is fundamental. Especially in the case of epilepsy, cognitive dysfunctions such as memory or attentional problems are often present additionally to seizures. Neurofeedback (or EEG-biofeedback) is a psychological technique that, as a supplement to medication and surgical therapies, has been demonstrated to provide further improvement in many neurological diseases, including epilepsy. However, most efforts of neurofeedback have traditionally been dedicated to the reduction of seizure frequency, and little attention has been paid for improving cognitive deficits by means of specific electrophysiological changes. Furthermore, current neurofeedback approaches are not suitable for these purposes because the parameters used do not take into consideration the relationship between memory performance and event-induced brain activity. Considering all these aspects, the cognitive performance of a group of epilepsy patients and a group of healthy controls was analyzed based on the event-related de /synchronization (ERD/ERS) method. Significant differences between both populations in the theta and upper alpha bands were observed. These findings support the possible exploitation of cognitive quantitative parameters in epilepsy based on ERD/ERS. An algorithm for the online ERD/ERS calculation was selected for future neurofeedback applications, as the result of a comparative dynamic study. Subsequently, a methodology for the online extraction and quantification of cognitive-induced brain activity was developed based on the selected algorithm. The procedure is functionally organized in blocks of algorithms in order to increase applicability. Several aspects, including the role of electrode montages and the reduction or minimization of the evoked activity, were examined based on cognitive studies as part of the optimization process. Future steps should include the design of a special training paradigm as well as a pilot study for confirming the theoretical approach proposed in this work

Measuring High-Order Interactions in Rhythmic Processes through Multivariate Spectral Information Decomposition

Many complex systems in physics, biology and engineering are modeled as dynamical networks and described using multivariate time series analysis. Recent developments have shown that the emergent dynamics of a network system are significantly affected by interactions involving multiple network nodes which cannot be described using pairwise links. While these higher-order interactions can be probed using information-theoretic measures, a rigorous framework to describe them in the frequency domain is still lacking. This work presents an approach for the spectral decomposition of multivariate information measures, capable of identifying higher-order synergistic and redundant interactions between oscillatory processes. We show theoretically that synergy and redundancy can coexist at different frequencies among the output signals of a network system and can be detected only using the proposed spectral method. To demonstrate the broad applicability of the framework, we provide parametric and non-parametric data-efficient estimators for the spectral information measures, and employ them to describe multivariate interactions in three complex systems producing rich oscillatory dynamics, namely the human brain, a ring of electronic oscillators, and the global climate system. In these systems, we show that the use of our framework for the spectral decomposition of information measures reveals multivariate and higher-order interactions not detectable in the time domain. Our results are exemplary of how the frequency-specific analysis of multivariate dynamics can aid the implementation of assessment and control strategies in realworld network systems

Network-based brain computer interfaces: principles and applications

Brain-computer interfaces (BCIs) make possible to interact with the external environment by decoding the mental intention of individuals. BCIs can therefore be used to address basic neuroscience questions but also to unlock a variety of applications from exoskeleton control to neurofeedback (NFB) rehabilitation. In general, BCI usability critically depends on the ability to comprehensively characterize brain functioning and correctly identify the user s mental state. To this end, much of the efforts have focused on improving the classification algorithms taking into account localized brain activities as input features. Despite considerable improvement BCI performance is still unstable and, as a matter of fact, current features represent oversimplified descriptors of brain functioning. In the last decade, growing evidence has shown that the brain works as a networked system composed of multiple specialized and spatially distributed areas that dynamically integrate information. While more complex, looking at how remote brain regions functionally interact represents a grounded alternative to better describe brain functioning. Thanks to recent advances in network science, i.e. a modern field that draws on graph theory, statistical mechanics, data mining and inferential modelling, scientists have now powerful means to characterize complex brain networks derived from neuroimaging data. Notably, summary features can be extracted from these networks to quantitatively measure specific organizational properties across a variety of topological scales. In this topical review, we aim to provide the state-of-the-art supporting the development of a network theoretic approach as a promising tool for understanding BCIs and improve usability

An Investigation on the Utility and Reliability of Electroencephalogram Phase Signal Upon Interpreting Cognitive Responses in the Brain: A Critical Discussion

International audienceWithin the neuroscience and computational neuroscience communities, applications such as evaluating different cognitive responses of the brain, brain-computer interface (BCI) systems and brain connectivity studies have increasingly been using EEG phase information during the past few decades. The utility of EEG phase can be directly linked to the neural propagation and synchronized firing of neuronal populations during different cognitive states of the brain. Nevertheless, it has previously been shown that phase of narrow-band (frequency specific) foreground EEG (desired) is prone to contain fake spikes and variations (unrelated to brain activity) in the presence of background spontaneous EEG and low SNRs of foreground EEG (the low-amplitude analytic signals or LAAS problem). Accordingly, extracting the instantaneous EEG phase sequence for further utilization upon interpreting the cognitive states of the brain using phase related quantities, such as instantaneous frequency, phase shift, phase resetting and phase locking value, is a very sensitive and rigorous process. In this study, a simple procedure is proposed to illustrate the effects of LAAS problem on the utility of EEG phase related quantities in aforementioned applications, also to investigate the reliability of interpretations of the brain's cognitive states based on such quantities. Results show that, without a proper and effective solution strategy, such potential flaws lead to incorrect physiological and pathological interpretations