Revisión sistemática de la aplicación de algoritmos de «machine learning» en la esclerosis múltiple / A systematic review of the application of machine-learning algorithms in multiple sclerosis

Introducción: La aplicación de la inteligencia artificial y en particular de algoritmos de aprendizaje automático o «machine learning» (ML) constituye un desafío y al mismo tiempo una gran oportunidad en diversas disciplinas científicas, técnicas y clínicas. Las aplicaciones específicas en el estudio de la esclerosis múltiple (EM) no han sido una excepción mostrando un creciente interés en los últimos años. Objetivo: Realizar una revisión sistemática de la aplicación de algoritmos de ML en la EM. Material y métodos: Empleando el motor de búsqueda de libre acceso PubMed que accede a la base de datos MEDLINE, se seleccionaron aquellos estudios que incluyeran simultáneamente los dos siguientes conceptos de búsqueda: «machine learning» y «multiple sclerosis». Se rechazaron aquellos estudios que fueran revisiones, estuvieran en otro idioma que no fuera el castellano o el inglés, y aquellos trabajos que tuvieran un carácter técnico y no fueran aplicados para la EM. Se seleccionaron como válidos 76 artículos y fueron rechazados 38. Conclusiones: Tras la revisión de los estudios seleccionados, se pudo observar que la aplicación del ML en la EM se concentró en cuatro categorías: 1) clasificación de subtipos de pacientes dentro de la enfermedad; 2) diagnóstico del paciente frente a controles sanos u otras enfermedades; 3) predicción de la evolución o de la respuesta a intervenciones terapéuticas y por último 4) otros enfoques. Los resultados hallados hasta la fecha muestran que los diferentes algoritmos de ML pueden ser un gran apoyo para el profesional sanitario tanto en la clínica como en la investigación de la EM.(AU)

Introduction: The applications of artificial intelligence, and in particular automatic learning or “machine learning” (ML), constitute both a challenge and a great opportunity in numerous scientific, technical, and clinical disciplines. Specific applications in the study of multiple sclerosis (MS) have been no exception, and constitute an area of increasing interest in recent years. Objective: We present a systematic review of the application of ML algorithms in MS. Materials and methods: We used the PubMed search engine, which allows free access to the MEDLINE medical database, to identify studies including the keywords “machine learning” and “multiple sclerosis.” We excluded review articles, studies written in languages other than English or Spanish, and studies that were mainly technical and did not specifically apply to MS. The final selection included 76 articles, and 38 were rejected. Conclusions: After the review process, we established 4 main applications of ML in MS: 1) classifying MS subtypes; 2) distinguishing patients with MS from healthy controls and individuals with other diseases; 3) predicting progression and response to therapeutic interventions; and 4) other applications. Results found to date have shown that ML algorithms may offer great support for health professionals both in clinical settings and in research into MS.(AU)

Redes neurales atencionales en enfermedades neurodegenerativas: evidencias anatómico-funcionales empleando el Attention Network Test / Attentional networks in neurodegenerative diseases: anatomical and functional evidence from the Attention Network Test

Introducción: Comprender las alteraciones en la anatomía y función del cerebro en los procesos cognitivos para las enfermedades neurodegenerativas es aún un desafío para la neurociencia actual. Desde la neurociencia experimental algunos test computarizados han sido desarrollados para mejorar nuestro conocimiento de las redes neurales involucradas en la cognición. El Attention Network Test (ANT) permite medir la activad de las 3 redes atencionales (alerta, orientación y función ejecutiva).ObjetivosEl principal objetivo de esta revisión fue describir todas las alteraciones anatómicas y funcionales encontradas en diversas enfermedades neurológicas usando el ANT.Material y métodosUn protocolo de revisión fue aplicado seleccionando estudios desde 2010 en la base de datos PubMed, que involucraban al ATN en diferentes enfermedades neurológicas. Se obtuvieron 32 artículos para esclerosis múltiple, epilepsia o Parkinson entre otras enfermedades.ConclusionesSe confirman algunas de las estructuras anatómicas propuestas para el modelo de 3 grandes redes atencionales. Las estructuras más relevantes para la red de alerta son la corteza prefrontal, las regiones parietales, el tálamo y el cerebelo. El tálamo es también relevante para la red de orientación, junto a regiones parietales posteriores. Respecto a la red ejecutiva no depende exclusivamente de la corteza prefrontal y corteza cingulada anterior, sino también de estructuras subcorticales como los ganglios basales y el cerebelo y sus proyecciones hacia toda la corteza. (AU)

Introduction: Understanding alterations to brain anatomy and cognitive function associated with neurodegenerative diseases remains a challenge for neuroscience today. In experimental neuroscience, several computerised tests have been developed to contribute to our understanding of neural networks involved in cognition. The Attention Network Test (ANT) enables us to measure the activity of 3 attentional networks (alertness, orienting, and executive function).ObjectivesThe main aim of this review is to describe all the anatomical and functional alterations found in diverse neurological diseases using the ANT.Material and methodsWe collected studies published since 2010 in the PubMed database that employed the ANT in different neurological diseases. Thirty-two articles were obtained, addressing multiple sclerosis, epilepsy, and Parkinson's disease, among other disorders.ConclusionsSome of the anatomical structures proposed in the 3 attentional networks model were confirmed. The most relevant structures in the alertness network are the prefrontal cortex, parietal region, thalamus, and cerebellum. The thalamus is also relevant in the orienting network, together with posterior parietal regions. The executive network does not depend exclusively on the prefrontal cortex and anterior cingulate cortex, but also involves such subcortical structures as the basal ganglia and cerebellum and their projections towards the entire cortex. (AU)

Attentional networks in neurodegenerative diseases: anatomical and functional evidence from the Attention Network Test.

INTRODUCTION: Understanding alterations to brain anatomy and cognitive function associated with neurodegenerative diseases remains a challenge for neuroscience today. In experimental neuroscience, several computerised tests have been developed to contribute to our understanding of neural networks involved in cognition. The Attention Network Test (ANT) enables us to measure the activity of 3 attentional networks (alertness, orienting, and executive function). OBJECTIVES: The main aim of this review is to describe all the anatomical and functional alterations found in diverse neurological diseases using the ANT. MATERIAL AND METHODS: We collected studies published since 2010 in the PubMed database that employed the ANT in different neurological diseases. Thirty-two articles were obtained, addressing multiple sclerosis, epilepsy, and Parkinson's disease, among other disorders. CONCLUSIONS: Some of the anatomical structures proposed in the 3 attentional networks model were confirmed. The most relevant structures in the alertness network are the prefrontal cortex, parietal region, thalamus, and cerebellum. The thalamus is also relevant in the orienting network, together with posterior parietal regions. The executive network does not depend exclusively on the prefrontal cortex and anterior cingulate cortex, but also involves such subcortical structures as the basal ganglia and cerebellum and their projections towards the entire cortex.

A systematic review of the application of machine-learning algorithms in multiple sclerosis.

INTRODUCTION: The applications of artificial intelligence, and in particular automatic learning or "machine learning" (ML), constitute both a challenge and a great opportunity in numerous scientific, technical, and clinical disciplines. Specific applications in the study of multiple sclerosis (MS) have been no exception, and constitute an area of increasing interest in recent years. OBJECTIVE: We present a systematic review of the application of ML algorithms in MS. MATERIALS AND METHODS: We used the PubMed search engine, which allows free access to the MEDLINE medical database, to identify studies including the keywords "machine learning" and "multiple sclerosis." We excluded review articles, studies written in languages other than English or Spanish, and studies that were mainly technical and did not specifically apply to MS. The final selection included 76 articles, and 38 were rejected. CONCLUSIONS: After the review process, we established 4 main applications of ML in MS: 1) classifying MS subtypes; 2) distinguishing patients with MS from healthy controls and individuals with other diseases; 3) predicting progression and response to therapeutic interventions; and 4) other applications. Results found to date have shown that ML algorithms may offer great support for health professionals both in clinical settings and in research into MS.

A systematic review of the application of machine-learning algorithms in multiple sclerosis. / Revisión sistemática de la aplicación de algoritmos de «machine learning¼ en la esclerosis múltiple.

INTRODUCTION: The applications of artificial intelligence, and in particular automatic learning or "machine learning" (ML), constitute both a challenge and a great opportunity in numerous scientific, technical, and clinical disciplines. Specific applications in the study of multiple sclerosis (MS) have been no exception, and constitute an area of increasing interest in recent years. OBJECTIVE: We present a systematic review of the application of ML algorithms in MS. MATERIALS AND METHODS: We used the PubMed search engine, which allows free access to the MEDLINE medical database, to identify studies including the keywords "machine learning" and "multiple sclerosis." We excluded review articles, studies written in languages other than English or Spanish, and studies that were mainly technical and did not specifically apply to MS. The final selection included 76 articles, and 38 were rejected. CONCLUSIONS: After the review process, we established 4 main applications of ML in MS: 1) classifying MS subtypes; 2) distinguishing patients with MS from healthy controls and individuals with other diseases; 3) predicting progression and response to therapeutic interventions; and 4) other applications. Results found to date have shown that ML algorithms may offer great support for health professionals both in clinical settings and in research into MS.

Altered phase and nonphase EEG activity expose impaired maintenance of a spatial-object attentional focus in multiple sclerosis patients.

Some of the anatomical and functional basis of cognitive impairment in multiple sclerosis (MS) currently remains unknown. In particular, there is scarce knowledge about modulations in induced EEG (nonphase activity) for diverse frequency bands related to attentional deficits in this pathology. The present study analyzes phase and nonphase alpha and gamma modulations in 26 remitting-relapsing multiple sclerosis patients during their participation in the attention network test compared with twenty-six healthy controls (HCs) matched in sociodemographic variables. Behavioral results showed that the MS group exhibited general slowing, suggesting impairment in alerting and orienting networks, as has been previously described in other studies. Time-frequency analysis of EEG revealed that the gamma band was related to the spatial translation of the attentional focus, and the alpha band seemed to be related to the expectancy mechanisms and cognitive processing of the target. Moreover, phase and nonphase modulations differed in their psychophysiological roles and were affected differently in the MS and HC groups. In summary, nonphase modulations can unveil hidden cognitive mechanisms for phase analysis and complete our knowledge of the neural basis of cognitive impairment in multiple sclerosis pathology.

Attentional networks in neurodegenerative diseases: anatomical and functional evidence from the Attention Network Test. / Redes neurales atencionales en enfermedades neurodegenerativas: evidencias anatómico-funcionales empleando el Attention Network Test.

INTRODUCTION: Understanding alterations to brain anatomy and cognitive function associated with neurodegenerative diseases remains a challenge for neuroscience today. In experimental neuroscience, several computerised tests have been developed to contribute to our understanding of neural networks involved in cognition. The Attention Network Test (ANT) enables us to measure the activity of 3 attentional networks (alertness, orienting, and executive function). OBJECTIVES: The main aim of this review is to describe all the anatomical and functional alterations found in diverse neurological diseases using the ANT. MATERIAL AND METHODS: We collected studies published since 2010 in the PubMed database that employed the ANT in different neurological diseases. Thirty-two articles were obtained, addressing multiple sclerosis, epilepsy, and Parkinson's disease, among other disorders. CONCLUSIONS: Some of the anatomical structures proposed in the 3 attentional networks model were confirmed. The most relevant structures in the alertness network are the prefrontal cortex, parietal region, thalamus, and cerebellum. The thalamus is also relevant in the orienting network, together with posterior parietal regions. The executive network does not depend exclusively on the prefrontal cortex and anterior cingulate cortex, but also involves such subcortical structures as the basal ganglia and cerebellum and their projections towards the entire cortex.

[The Attention Network Test in the study of cognitive impairment of ADHD patients]. / El Attention Network Test en el estudio de los déficits cognitivos de pacientes con trastorno por déficit de atención.

INTRODUCTION: The Attention Network Test (ANT) has been applied to the study of potential attentional impairments in diverse neuropathologies in the last years. This test allows analyzing of different networks involved in attentional processing (alerting, orientation and executive system). DEVELOPMENT: A specific application of ANT in ADHD patients shows that it is possible to find diverse impairments in the three attentional networks and even some studies revealed no alterations. Potential causes of this heterogeneity in the results could be based in methodological variations between studies, other pathological conditions in the participants and the network effects calculation that has been probed that could be wrongly interpreted. CONCLUSIONS: Despite the lack of conclusive results, this test shows multiple applications that would allow disentangling diverse cognitive impairments in ADHD patients. ANT could analyze diverse cognitive mechanisms that could be compromised in these patients (tonic and phasic alerting, temporal and spatial expectancy, degree of interference of the distractor stimuli, attentional blinking o inhibition of return). This test could help to perform a better characterization of ADHD patients further than the classical forms considered nowadays (unattended and combined).

TITLE: El Attention Network Test en el estudio de los déficits cognitivos de pacientes con trastorno por déficit de atención.Introducción. El Attention Network Test (ANT) se ha aplicado en el estudio de las posibles alteraciones atencionales en diversas neuropatologías en los últimos años. Este test permite el análisis de diversas redes implicadas en el proceso atencional (alerta, orientación y sistema ejecutivo). Desarrollo. La aplicación particular del ANT en pacientes con trastorno por déficit de atención muestra que es posible encontrar diversas alteraciones de las tres redes atencionales según los estudios e incluso, en algunos casos, la ausencia de alteraciones en ellas. Las posibles causas de esta heterogeneidad pueden deberse a variaciones metodológicas en la aplicación del test, otras condiciones patológicas no consideradas de los pacientes y el análisis de redes sugerido por los creadores del modelo y que se ha demostrado en diversos estudios que puede llevar a interpretaciones erróneas. Conclusiones. A pesar de los resultados todavía poco concluyentes con la aplicación del ANT en el trastorno por déficit de atención, este test muestra múltiples aplicaciones que permitirán desentrañar los diversos déficits cognitivos que están presentes en los pacientes con trastorno por déficit de atención. Entre ellos, el test puede analizar diversos mecanismos que pueden estar afectados en estos pacientes (la alerta tónica y fásica, la expectativa temporal o espacial, el grado de interferencia de los estímulos distractores, el parpadeo atencional o la inhibición de retorno). El ANT puede ayudar a una mejor caracterización de los pacientes con trastorno por déficit de atención más allá de las formas clásicas consideradas hasta ahora (inatento o combinado).

EEG study on affective valence elicited by novel and familiar pictures using ERD/ERS and SVM-RFE.

EEG signals have been widely explored in emotional processing analyses, both in time and frequency domains. However, in such studies, habituation phenomenon is barely considered in the discrimination of different emotional responses. In this work, spectral features of the event-related potentials (ERPs) are studied by means of event-related desynchronization/synchronization computation. In order to determine the most relevant ERP features for distinguishing how positive and negative affective valences are processed within the brain, support vector machine-recursive feature elimination is employed. The proposed approach was applied for investigating in which way the familiarity of stimuli affects the affective valence processing as well as which frequency bands and scalp regions are more involved in this process. In a group composed of young adult women, results prove that parietooccipital region and theta band are especially involved in the processing of novelty in emotional stimuli. Furthermore, the proposed method has shown to perform successfully using a moderated number of trials.

Individual EEG differences in affective valence processing in women with low and high neuroticism.

OBJECTIVE: In this study, individual differences in brain electrophysiology during positive and negative affective valence processing in women with different neuroticism scores are quantified. METHODS: Twenty-six women scoring high and low on neuroticism participated on this experiment. A support vector machine (SVM)-based classifier was applied on the EEG single trials elicited by high arousal pictures with negative and positive valence scores. Based on the accuracy values obtained from subject identification tasks, the most distinguishing EEG channels among participants were detected, pointing which scalp regions show more distinct patterns. RESULTS: Significant differences were obtained, in the EEG heterogeneity between positive and negative valence stimuli, yielding higher accuracy in subject identification using negative pictures. Regarding the topographical analysis, significantly higher accuracy values were reached in occipital areas and in the right hemisphere (p < 0.001). CONCLUSIONS: Mainly, individual differences in EEG can be located in parietooccipital regions. These differences are likely to be due to the different reactivity and coping strategies to unpleasant stimuli in individuals with high neuroticism. In addition, the right hemisphere shows a greater individual specificity. SIGNIFICANCE: An SVM-based classifier asserts the individual specificity and its topographical differences in electrophysiological activity for women with high neuroticism compared to low neuroticism.

Potenciales evocados cognitivos en pacientes con esclerosis múltiple remitente-recurrente y benigna / Cognitive evoked potentials in remiting-relapsing and benign forms of multiple sclerosis

Introducción. Conseguir una evaluación mejor del deterioro cognitivo en la esclerosis múltiple es uno de los grandes retos actuales. Un objetivo esencial es obtener, desde diferentes aproximaciones, la valoración objetiva del déficit, y que permitan su correlación con variables fisiológicas. Objetivo. Analizar las posibles modulaciones en componentes fisiológicos del procesamiento de la información relacionados con un déficit atencional en pacientes con diversos tipos de esclerosis múltiple. Sujetos y métodos. Participaron en el presente estudio 17 pacientes con esclerosis múltiple remitente-recurrente, nueve pacientes con esclerosis múltiple benigna y 19 sujetos sanos. Se registraron sus respuestas conductuales en una tarea visuoespacial y, posteriormente, se realizó una prueba oddball auditiva en la que se registró la señal de electroencefalografía para la obtención de los potenciales evocados cognitivos. Se realizaron, asimismo, análisis de correlación entre las variables fisiológicas con variables clínicas propias del paciente. Resultados. Se encontraron un retraso en los tiempos de reacción durante el desarrollo de la tarea de Posner y un retraso en la latencia del componente P3 durante la realización de la tarea oddball en ambos grupos de pacientes con esclerosis múltiple. Conclusión. Los resultados obtenidos en este experimento confirman la presencia de deterioro atencional en ambos grupos de pacientes. La modulación exclusiva de la latencia del componente P3 sugiere que el deterioro atencional en estos pacientes al comienzo de la enfermedad se localiza en el procesamiento cognitivo central y, en principio, es producto de la desmielinización (AU)

Introduction. The assessment of the cognitive impairment in the multiple sclerosis disease is one of the most relevant challenges nowadays. An essential objective is to obtain diverse approaches that allow valuing objectively this impairment and its correlation with physiological variables. Aim. To analyze the possible modulations in physiological components of the information processing (ERPs) related with an attentional deficit in diverse classes of patients with multiple sclerosis. Subjects and methods. 17 patients with remitting-relapsing multiple sclerosis, 9 patients with benign multiple sclerosis and 19 healthy subjects participated in the study. Behavioral performance in a visuo-spatial task (Posner paradigm) and later, an auditory oddball test was carried out where electroencephalography signal was registered to obtain ERPs. Correlation analyses were calculated between patient variables (EDSS or disease duration) and psychophysiological variables. Results. A delay in the reaction time during the development of the Posner task and a delay in the latency of the component P3 during the realization of the oddball task were found in both groups of patient with multiple sclerosis. Conclusion. The data obtained in this experiment confirm the presence of attentional impairment in patients with diverse forms of multiple sclerosis. The exclusive modulation of the P3 latency component suggests that the impairment in these patients, at the beginning of the disease, is localized at a central level of cognitive processing and is product of the demyelinating process (AU)

[Cognitive evoked potentials in remitting-relapsing and benign forms of multiple sclerosis]. / Potenciales evocados cognitivos en pacientes con esclerosis multiple remitente-recurrente y benigna.

INTRODUCTION: The assessment of the cognitive impairment in the multiple sclerosis disease is one of the most relevant challenges nowadays. An essential objective is to obtain diverse approaches that allow valuing objectively this impairment and its correlation with physiological variables. AIM: To analyze the possible modulations in physiological components of the information processing (ERPs) related with an attentional deficit in diverse classes of patients with multiple sclerosis. SUBJECTS AND METHODS: 17 patients with remitting-relapsing multiple sclerosis, 9 patients with benign multiple sclerosis and 19 healthy subjects participated in the study. Behavioral performance in a visuo-spatial task (Posner paradigm) and later, an auditory oddball test was carried out where electroencephalography signal was registered to obtain ERPs. Correlation analyses were calculated between patient variables (EDSS or disease duration) and psychophysiological variables. RESULTS: A delay in the reaction time during the development of the Posner task and a delay in the latency of the component P3 during the realization of the oddball task were found in both groups of patient with multiple sclerosis. CONCLUSION: The data obtained in this experiment confirm the presence of attentional impairment in patients with diverse forms of multiple sclerosis. The exclusive modulation of the P3 latency component suggests that the impairment in these patients, at the beginning of the disease, is localized at a central level of cognitive processing and is product of the demyelinating process.

Abnormal ERPs and high frequency bands power in multiple sclerosis.

Event-related potentials (ERPs) and power spectral density (PSD) were registered during an auditory-oddball paradigm in 11 MS patients. These patients showed a decrease in the amplitude of P2 and N2 components and a delayed P3 latency compared to control subjects suggesting that the attentional orienting mechanism in the auditory modality is affected in MS. The PSD analysis showed that MS patients exhibited an increased power in beta and gamma bands. The combined analysis of frequency and time domain suggested diverse phenomena that occurred in the MS patient group related with the EEG background or the motivational status.

[Gender-specific post-stimulus modulation in the alpha band during visual-spatial attention]. / Modulación postestímulo generoespecífica en la banda alfa durante la atención visuoespacial.

INTRODUCTION: Previous studies of the spontaneous activity of the EEG indicate that women present bigger absolute spectral power in the alpha band than men, but few studies have been done during cognitive activity. AIM: To check possible gender differences in the EEG frequency domain during a visuo-spatial attentional task to understand better the temporary dynamics of alpha. SUBJECTS AND METHODS: A classic oddball paradigm was used whose stimuli (90% standard-10% objectives) were complex. In each block (10 with 100 trials) it was requested to the subjects (20, 10 of each gender) to attend to one of the visual fields (left and right, with random stimuli and identical probability). Power spectral density values were calculated applying the fast Fourier transform in the alpha band (9-11 Hz) in two overlapped windows (sliding windows): of 0-512 ms and of 412-924 ms. RESULTS: The normalized data were analyzed by means of ANOVAs, with the following factors: gender, attention, hemisphere, visual field and electrodes. CONCLUSIONS: Different modulations were obtained attending to the gender variable: men showed smaller alpha or bigger suppression of the rhythm in posterior electrodes and women exhibited smaller power in anterior electrodes.

Modulación postestímulo generoespecífica en la banda alfa durante la atención visuoespacial / Gender-specific post-stimulus modulation in the alpha band during visual-spatial attention

Introducción. Estudios previos de la actividad espontánea del EEG indican que las mujeres presentan mayor potencia espectral absoluta en la banda a que los hombres, pero existen escasos trabajos realizados durante actividad cognitiva. Objetivo. Comprobar posibles diferencias de género en el dominio de la frecuencia del EEG durante la realización de una tarea que requiere un procesamiento cognitivo de atención visuoespacial en dos intervalos sucesivos, desde la llegada del estímulo para comprender mejor la modulación y su dinámica temporal. Sujetos y métodos. Se utilizó un paradigma oddball clásico, cuyos estímulos (90 por ciento estándares-10 por ciento objetivos) eran complejos. En cada bloque (10 de 100 ensayos) se pidió al sujeto (20, 10 de cada género) que atendiera alternativamente a un solo campo visual (estímulos aleatorios y equiprobables). Al registro EEG se le aplicó la transformada rápida de Fourier para obtener la densidad de potencia espectral de la banda a (9-11 Hz) en dos ventanas solapadas (sliding windows): de 0-512 y de 412-924 ms. Resultados. Los datos normalizados se analizaron mediante ANOVA, con los factores: género, atención, hemisferio, campo visual y electrodos. Conclusiones. Se obtienen modulaciones de sentido opuesto en hombres y mujeres. Los hombres presentaron menos a o mayor supresión en electrodos posteriores y las mujeres presentaron menos en electrodos anteriores para la banda (AU)

Introduction. Previous studies of the spontaneous activity of the EEG indicate that women present bigger absolute spectral power in the alpha band than men, but few studies have been done during cognitive activity. Aim. To check possible gender differences in the EEG frequency domain during a visuo-spatial attentional task to understand better the temporary dynamics of alpha. Subjects and methods. A classic oddball paradigm was used whose stimuli (90% standard-10% objectives) were complex. In each block (10 with 100 trials) it was requested to the subjects (20, 10 of each gender) to attend to one of the visual fields (left and right, with random stimuli and identical probability). Power spectral density values were calculated applying the fast Fourier transform in the alpha band (9-11 Hz) in two overlapped windows (sliding windows): of 0-512 ms and of 412-924 ms. Results. The normalized data were analyzed by means of ANOVAs, with the following factors: gender, attention, hemisphere, visual field and electrodes. Conclusions. Different modulations were obtained attending to the gender variable: men showed smaller alpha or bigger suppression of the rhythm in posterior electrodes and women exhibited smaller power in anterior electrodes (AU)

Temporal evolution of alpha and beta bands during visual spatial attention.

Event-related potentials (ERPs) are an electrophysiological index of various cognitive processes such as attention. However, this kind of analysis does not allow observation of differences in the spectral content taking place during a sensory, cognitive or motor task. The goal of the present work was to compute the temporal dynamics of EEG oscillations using a technique called temporal spectral evolution (TSE). The electroencephalogram (EEG) was recorded during the presentation of flashed stimuli that were randomly presented to the left or right visual field. Subjects were asked to pay attention, alternately in different blocks of trials, to the left or to the right to detect an infrequent target. The results showed a decrease in the alpha band in a time window of 375-500 ms and an increase in the beta band at 500-875 ms after stimulus onset, for both attended and unattended stimuli. Statistical analysis showed that the decrease in alpha and the increase in beta were more marked during the attentional condition. In conclusion, these results demonstrate that the decrease in alpha band and the increase in beta band are electrophysiological markers of visual spatial attention.