Extracción y clasificación de características aplicados a señales electroencefalográficas en sistemas Brain Computer Interface basados en potenciales evocados P300

Los sistemas Brain Computer Interface (BCI) permiten enviar mensajes y órdenes al mundo externo sin necesidad de realizar ninguna actividad muscular. Estos programas pueden habilitar a personas con discapacidades neuromusculares severas como la esclerosis lateral amiotrófica, ataque cerebral y lesiones de la médula espinal para comunicarse y utilizar programas y equipos de diversos tipos que mejoran su calidad de vida. Para conseguir este objetivo, se usan una serie de señales electroencefalográficas registradas en el cuero cabelludo en las cuáles está codificada la intención del usuario. En este estudio nos centramos en una de ellas: los potenciales evocados P300. El objetivo de este proyecto es el estudio de algoritmos de extracción y clasificación de características en BCI basados en potenciales evocados P300, con el propósito de determinar los parámetros óptimos de todos los métodos utilizados para obtener la máxima precisión en la clasificación. Como métodos de extracción de características se proponen un sub-muestreo y extracción de características mediante transformada wavelet. A su vez se desarrolla un algoritmo de eliminación y selección de canales. En cuanto a la clasificación de características, se utilizan tres métodos: discriminante lineal de Fisher (FLDA), Spectral Regression Kernel Discriminant Analysis (SRKDA) y un conjunto de máquinas de vectores de soporte (SVM). Estos métodos se prueban sobre el conjunto de datos II de la III Competición BCI proporcionados por el centro Wadsworth (NYS Department of Health), con y sin eliminación de canales. Los resultados se comparan con los del algoritmo ganador de esa competición, el cual consistía en un conjunto de 17 SVM con selección de canales y con otros métodos del estado del arte que usaron la misma base de datos, así como los resultados obtenidos en un estudio preliminar de métodos de clasificación de características. Los resultados muestran que dos de los métodos propuestos (FLDA y SRKDA), con sub-muestreo y aplicación de transformada wavelet adaptados a cada sujeto, obtienen una precisión (99.5 % y 99 %) mayor que la del método ganador (96.5 %). Comparados con otros métodos del estado del arte, estos dos algoritmos obtienen unos resultados excelentes que los colocan en primer y segundo puesto de la clasificación global.Departamento de Teoría de la Señal y Comunicaciones e Ingeniería TelemáticaMáster en Ingeniería de Telecomunicació

Unveiling the alterations in the frequency-dependent connectivity structure of MEG signals in mild cognitive impairment and Alzheimer’s disease

Producción CientíficaMild cognitive impairment (MCI) and dementia due to Alzheimer’s disease (AD) are neurological disorders that affect cognition, brain function, and memory. Magnetoencephalography (MEG) is a neuroimaging technique used to study changes in brain oscillations caused by neural pathologies. However, MEG studies often use fixed frequency bands, assuming a common frequency structure and overlooking both subject-specific variations and the potential influence of pathologies on frequency distribution. To address this issue, a novel methodology called Connectivity-based Meta-Bands (CMB) was applied to obtain a subject-specific functional connectivity-based frequency bands segmentation. Resting-state MEG activity was acquired from 161 participants: 67 healthy controls, 44 MCI patients, and 50 AD patients. The CMB algorithm was used to identify “meta-bands” (i.e., recurrent network topologies across frequencies). The meta-bands were used to extract an individualised frequency band segmentation. The network topology of the meta-bands and their sequencing were analysed to identify alterations associated with MCI and AD in the underlying frequency-dependent connectivity structure. We found that MCI and AD alter the neural network topology, leading to connectivity patterns both more widespread in the frequency spectrum and heterogeneous. Furthermore, the meta-band frequency sequencing was modified, with MCI and AD patients exhibiting sequences with increased complexity, suggesting a progressive dilution of the frequency structure. The study highlights the relevance of considering the impact of neural pathologies on the frequency-dependent connectivity structure and the potential bias introduced by using fixed frequency bands in MEG studies.Bioingeniería, Biomateriales y Nanomedicina (CIBER-BBN)’ through ‘Instituto de Salud Carlos III’- FEDERERA-Net FLAG-ERA JTC2021 project ModelDXConsciousness (Human Brain Project Partnering Project

Exploring non-stationarity patterns in schizophrenia: neural reorganization abnormalities in the alpha band

Producción CientíficaObjective. The aim of this paper was to characterize brain non-stationarity during an auditory oddball task in schizophrenia (SCH). The level of non-stationarity was measured in the baseline and response windows of relevant tones in SCH patients and healthy controls. Approach. Event-related potentials were recorded from 28 SCH patients and 51 controls. Non-stationarity was estimated in the conventional electroencephalography frequency bands by means of Kullback-Leibler divergence (KLD). Relative power (RP) was also computed to assess a possible complementarity with KLD. Main results. Results showed a widespread statistically significant increase in the level of non-stationarity from baseline to response in all frequency bands for both groups. Statistically significant differences in non-stationarity were found between SCH patients and controls in beta-2 and especially in the alpha band. SCH patients showed more non-stationarity in the left parieto-occipital region during the baseline window in the beta-2 band. A leave-one-out cross validation classification study with feature selection based on binary stepwise logistic regression to discriminate between SCH patients and controls provided an accuracy of 89.87% and area under ROC of 0.9510. Significance. KLD can characterize transient neural reorganization during an attentional task in response to novelty and relevance. Our findings suggest anomalous reorganization of neural dynamics in SCH during an oddball task. The abnormal frequency-dependent modulation found in SCH patients during relevant tones is in agreement with the hypothesis of aberrant salience detection in SCH. The increase in non-stationarity in the alpha band during the active task supports the notion that this band is involved in top-down processing. The baseline differences in the beta-2 band suggest that hyperactivation of the default mode network during attention tasks may be related to SCH symptoms. Furthermore, the binary stepwise logistic regression procedure selected features from both KLD and RP, supporting the idea that these measures can be complementary.This research project was supported in part by the projects TEC2014-53196-R of ‘Ministerio de Economía y Competitividad’ and FEDER; the project VA037U16 from the “Consejería de Educación de la Junta de Castilla y León”, the “Fondo de Investigaciones Sanitarias (Instituto de Salud Carlos III)” under projects FIS PI11/02203 and PI15/00299; and the “Gerencia Regional de Salud de Castilla y León” under projects GRS 932/A/14 and GRS 1134/A/15. P. Núñez was in receipt of a ‘Promoción de empleo joven e implantación de la Garantía Juvenil en I+D+i’ grant from ‘Ministerio de Economía y Competitividad’ and the University of Valladolid, A. Bachiller and J. Gomez-Pilar were in receipt of a PIF-UVA grant from the University of Valladolid. A. Lubeiro has a predoctoral scholarship from the “Junta de Castilla y León” and European Social Fund

Analysis of Functional Connectivity during an Auditory Oddball Task in Schizophrenia

Producción CientíficaThe aim of this study was to evaluate neural coupling patterns in schizophrenia (SCH) patients and healthy controls during an auditory oddball task. Two measures of functional connectivity were applied to 28 SCH patients and 51 healthy controls to characterize electroencephalographic (EEG) activity. Specifically, magnitude squared coherence (MSC) and the imaginary part of coherency (ICOH) were computed for five frequency bands: theta, alpha, beta-1, beta-2 and gamma. The results showed a statistically significant modulation increase in MSC and ICOH for controls with respect to SCH in the theta band, and a decrease in ICOH for the beta-2 band. Furthermore, controls showed more significant changes from the baseline and active task windows than SCH patients. Our findings suggest that SCH patients show coupling abnormalities during an auditory oddball task compared to healthy controls.Ministerio de Economía y Competitividad (TEC2014-53196-R)Junta de Castilla y León (VA059U13

Novel Measure of the Weigh Distribution Balance on the Brain Network: Graph Complexity Applied to Schizophrenia

Producción CientíficaThe aim of this study was to assess brain complexity dynamics in schizophrenia (SCH) patients during an auditory oddball task. For that task, we applied a novel graph measure based on the balance of the node weighs distribution. Previous studies applied complexity parameters that were strongly dependent on network topology. This fact could bias the results besides being necessary correction techniques as surrogating process. In the present study, we applied a novel graph complexity measure from the information theory: Shannon Graph Complexity (SGC). Complexity patterns form electroencephalographic recordings of 20 healthy controls and 20 SCH patients during an auditory oddball task were analyzed. Results showed a significantly more pronounced decrease of SGC for controls than for SCH patients during the cognitive task. These findings suggest an important change in the brain configuration towards more balanced networks, mainly in the connections related to long-range interactions. Since these changes are significantly more pronounced in controls, it implies a deficit in the neural network reorganization in SCH patients. In addition, SGC showed a suitable discrimination ability using a leave-one-out cross-validation: 0.725 accuracy and 0.752 area under receiver operating characteristics curve. The novel complexity measure proposed in this study demonstrated to be independent of network topology and, therefore, it complements traditional graph measures to characterize brain networks.Ministerio de Economía y Competitividad (TEC2014-53196-R)Junta de Castilla y León (VA059U13

Analysis of the Non-stationarity of Neural Activity during an Auditory Oddball Task in Schizophrenia

Producción CientíficaThe aim of this study was to characterize brain dynamics during an auditory oddball task. For this purpose, a measure of the non-stationarity of a given time-frequency representation (TFR) was applied to electroencephalographic (EEG) signals. EEG activity was acquired from 20 schizophrenic (SCH) patients and 20 healthy controls while they underwent a three-stimulus auditory oddball task. The Degree of Stationarity (DS), a measure of the non-stationarity of the TFR, was computed using the continuous wavelet transform. DS was calculated for both the baseline [-300 0] ms and active task [150 550] ms windows of a P300 auditory oddball task. Results showed a statistically significant increase (p<0.05) in non-stationarity for controls during the cognitive task in the central region, while less widespread statistically significant differences were obtained for SCH patients, especially in the beta-2 and gamma bands. Our findings support the relevance of DS as a means to study cerebral processing in SCH. Furthermore, the lack of statistically significant changes in DS for SCH patients suggests an abnormal reorganization of neural dynamics during an oddball task.Ministerio de Economía y Competitividad (TEC2014-53196-R)Junta de Castilla y León (VA059U13

Relation between EEG resting-state power and modulation of P300 task-related activity in theta band in schizophrenia

Producción CientíficaThere is some consistency in previous EEG findings that patients with schizophrenia have increased resting-state cortical activity. Furthermore, in previous work, we have provided evidence that there is a deficit in the modulation of bioelectrical activity during the performance of a P300 task in schizophrenia. Our hypothesis here is that a basal hyperactivation would be related with altered ability to change or modulate cortical activity during a cognitive task. However, no study so far, to the best of our knowledge, has studied the association between resting-state activity and task-related modulation. With this aim, we used a dual EEG paradigm (resting state and oddball task for elicitation of the P300 evoked potential) in a sample of patients with schizophrenia (n = 100), which included a subgroup of patients with first episode psychosis (n = 30), as well as a group of healthy controls (n = 93). The study measures were absolute power for resting-state; and spectral entropy (SE) and connectivity strength (CS) for P300-task data, whose modulation had been previously found to be altered in schizophrenia. Following the literature on P300, we focused our study on the theta frequency band. As expected, our results showed an increase in resting state activity and altered task-related modulation. Moreover, we found an inverse relationship between the amount of resting-state activity and modulation of task-related activity. Our results confirm our hypothesis and support the idea that a greater amount of resting theta-band synchrony could hamper the modulation of signal regularity (quantified by SE) and activity density (measured by CS) during the P300 task performance. This association was found in both patients and controls, suggesting the existence of a common mechanism and a possible ceiling effect in schizophrenia patients in relation to a decreased inhibitory function that limits their cortical reactivity to the task

Relations between structural and EEG-based graph metrics in healthy controls and schizophrenia patients

Producción CientíficaObjective: To assess using graph-theory properties of both structural and functional networks in schizophrenia patients, as well as the possible prediction of the latter based on the former. Abnormal structural and functional network parameters have been found in schizophrenia, but the dependence of functional network properties on structural alterations has not been described yet in this syndrome. Experimental design: We applied averaged path-length (PL), clustering coefficient (CLC) and density (D) measurements to structural data derived from diffusion magnetic resonance and functional data derived from electroencephalography in 39 schizophrenia patients and 79 controls. Functional data were collected for the global and theta frequency bands with subjects performing an odd-ball task, both prior to stimulus delivery and at the corresponding processing window. Connectivity matrices were constructed respectively from (i) tractography and registered cortical segmentations (structural) and (ii) phase-locking values (functional). Principal observations: In both groups, we observed a significant EEG task-related modulation (change between pre-stimulus and response windows) in the global and theta bands. Patients showed larger structural PL and pre-stimulus density in the global and theta bands, and lower PL task-related modulation in the theta band. Structural network values predicted pre-stimulus global band values in controls and global band task-related modulation in patients. Abnormal functional values found in patients (pre-stimulus density in the global and theta bands and task-related modulation in the theta band) were not predicted by structural data in this group. Structural and functional network abnormalities respectively predicted cognitive performance and positive symptoms in patients. Conclusions: Taken together, the alterations in the structural and functional theta networks in the patients and the lack of significant relations between these alterations, suggest that these types of network abnormalities exist in different groups of schizophrenia patients.This research project was supported in part by grants from Instituto de Salud Carlos III under project PI15/00299, “Gerencia Regional de Salud de Castilla y León” under projects GRS 1263/A/16 and GRS 1485/A/17, and “Ministerio de Economía y Competitividad” and FEDER under grants TEC2014-53196-R and TEC2013-44194-P; by ‘European Commission’ and FEDER under project 'Análisis y correlación entre el genoma completo y la actividad cerebral para la ayuda en el diagnóstico de la enfermedad de Alzheimer' ('Cooperation Programme Interreg V-A Spain-Portugal POCTEP 2014-2020'), and by ‘Consejería de Educación de la Junta de Castilla y León’ and FEDER under project VA037U16. J. Gomez-Pilar was in receipt of a grant from University of Valladolid and A. Lubeiro was in receipt of a grant from Consejería de Educación de la Junta de Castilla y León

Alterations of Effective Connectivity Patterns in Mild Cognitive Impairment: An MEG Study

Producción CientíficaNeuroimaging techniques have demonstrated over the years their ability to characterize the brain abnormalities associated with different neurodegenerative diseases. Among all these techniques, magnetoencephalography (MEG) stands out by its high temporal resolution and noninvasiveness. The aim of the present study is to explore the coupling patterns of resting-state MEG activity in subjects with mild cognitive impairment (MCI). To achieve this goal, five minutes of spontaneous MEG activity were acquired with a 148- channel whole-head magnetometer from 18 MCI patients and 26 healthy controls. Interchannel relationships were investigated by means of two complementary coupling measures: coherence and Granger causality. Coherence is a classical method of functional connectivity, while Granger causality quantifies effective (or causal) connectivity. Both measures were calculated in the five conventional frequency bands: delta (d, 1-4 Hz), theta (q, 4-8 Hz), alpha (a, 8-13 Hz), beta (b, 13-30 Hz), and gamma (g, 30-45Hz). Our results showed that connectivity values were lower for MCI patients than for controls in all frequency bands. However, only Granger causality revealed statistically significant differences between groups (p-values < 0.05, FDR corrected Mann-Whitney U-test), mainly in the beta band. Our results support the role of MCI as a disconnection syndrome, which elicits early alterations in effective connectivity patterns. These findings can be helpful to identify the neural substrates involved in prodromal stages of dementia.This research was supported by ‘Ministerio de Economía y Competitividad’ and ‘European Regional Development Fund’ under project TEC2014-53196-R, by ‘European Commission’ and ‘European Regional Development Fund’ under project ‘Análisis y correlación entre el genoma completo y la actividad cerebral para la ayuda en el diagnóstico de la enfermedad de Alzheimer’ (‘Cooperation Programme Interreg V-A Spain-Portugal POCTEP 2014-2020’), and by ‘Consejería de Educación de la Junta de Castilla y León’ under project VA037U16. Pablo Núñez was in receipt of a ‘Promoción de empleo joven e implantación de la Garantía Juvenil en I+D+i’ grant from ‘Ministerio de Economía y Competitividad’ and University of Valladolid

Libro de Actas de la "I Jornada para Alumnos de Trabajo Fin de Grado y Trabajo Fin de Máster: Uso Efectivo de Herramientas TIC"

Innovación EducativaEste libro de resúmenes engloba los trabajos presentados en la “I Jornada para alumnos de Trabajo Fin de Grado (TFG) y Trabajo Fin de Máster (TFM). Uso efectivo de herramientas TIC”, celebrada en Valladolid el 21 de marzo de 2019. Los trabajos aceptados tienen como autores a alumnos de TFG o TFM que han presentado su tema de estudio de TFG/TFM y los principales resultados obtenidos hasta el momento de acuerdo con los requisitos formales de la Jornada. Estos resúmenes cubren un amplio rango de temáticas, incluyendo el procesado de señales e imágenes o el diseño de dispositivos y redes de comunicaciones, entre otros. Todos los trabajos han seguido un proceso de revisión riguroso, siendo evaluados en profundidad por los miembros del Comité Organizador. Los editores del libro de resúmenes de la “I Jornada para alumnos de Trabajo Fin de Grado (TFG) y Trabajo Fin de Máster (TFM). Uso efectivo de herramientas TIC” agradecen enormemente a todos los alumnos, profesores y ponentes su participación en la Jornada, ya que su contribución ha sido imprescindible para la celebración de este evento.Vicerrectorado de Docencia de la Universidad de Valladolid (PID Nº 55: “Nuevas propuestas en la tutorización de Trabajos Fin de Grado y Trabajos Fin de Máster con el apoyo de entornos virtuales de aprendizaje colaborativo"