Oscilaciones cerebrales: papel fisiopatológico y terapéutico en algunas enfermedades neurológicas y psiquiátricas / Brain oscillations: pathophysiological and therapeutic role in some neurological and psychiatric diseases

Se usa el término «oscilación o actividad oscilatoria» para referirse a las fluctuaciones rítmicas de los potenciales postsinápticos de un grupo neuronal (potenciales de campo local) o de una región cortical (EEG, electrocorticografía) y también al patrón de descarga rítmico de los potenciales de acción de una neurona o un grupo neuronal. La actividad oscilatoria posibilita la sincronización entre grupos neuronales de la misma área cortical o de áreas distantes entre sí que intervienen en una acción motora, tarea cognitiva o perceptiva. Con frecuencia es motivo de confusión asociar la presencia de actividad oscilatoria con fenómenos de sincronización, ya que ambos fenómenos aunque relacionados no son equivalentes. En patologías neurológicas o psiquiátricas tan distintas como la enfermedad de Parkinson u otros movimientos anormales, la epilepsia o la esquizofrenia se han descrito anomalías de la actividad oscilatoria de distintas estructuras cerebrales o de su sincronización que podrían jugar un papel relevante en su fisiopatología. En esta revisión se discuten estos aspectos haciendo hincapié en su importancia por ser un mecanismo básico del funcionamiento cerebral y un nuevo mecanismo fisiopatólogico de la sintomatología de algunas enfermedades cerebrales (AU)

The terms «oscillations» or «oscillatory activity» are frequently used not only to define the rhythmic fluctuations of the postsynaptic potentials of a neuronal group (local field potentials) or a cortical region (EEG, MEG), but also to indicate the rhythmic discharge pattern of action potentials from a neuron or a small group of neurons. Oscillatory activity makes possible the synchronization of different neuronal groups from nearby or distant cortical regions that participate in the same motor, sensory or cognitive task. The presence of oscillatory activity is usually associated to the existence of synchronization, but both phenomena are not necessarily always equivalent. Abnormalities of oscillatory activities or synchronization within or between different brain structures have been described in several neurological and psychiatric diseases; these abnormalities might play a relevant pathophysiological role in Parkinson´s disease (and other movement disorders), schizophrenia or epilepsy. This review discusses all these aspects, with emphasis on their potential role both as a basic mechanism in brain function and as a pathophysiological substrate for some of the symptoms and signs observed in several diseases (AU)

Vídeo-electroencefalografía: una necesidad / Video-electroencephalography: a necessity

El vídeo-EEG es una herramienta diagnóstica habitual. Los avances técnicos de la última década la han simplificado de tal modo que con poco más de un ordenador y una cámara de vídeo pueden conseguirse registros de calidad. Se requiere personal preparado para su ejecución e interpretación. Es muy útil para el diagnóstico de episodios paroxísticos, para la clasificación y caracterización de crisis epilépticas y para la cuantificación de crisis o grafoelementos epileptiformes. Dada la importancia de un diagnóstico exacto, certero, ante un episodio paroxístico, no cabe duda de que esta herramienta debe ser cada vez más asequible para evitar el mal trato a muchos enfermos neurológicos. A pesar del paso de los años, un 20-30% de pacientes diagnosticados de epilepsia no son realmente epilépticos, lo cual sigue siendo excesivo e inaceptable (AU)

The video-EEG is a common diagnostic tool nowadays. The technical achievements of the last decade have brought a simplification of the equipment required to obtain good quality recordings, with little more than a computer and a video camera being necessary. However, the medical and technical staff must be well trained to execute and interpret the study. It is very useful in the diagnosis of paroxysmal events, for the classification and characterization of epileptic seizures and to quantify epileptiform discharges. Due to the importance of a correct diagnosis to avoid mistreating many neurological patients, this tool should be accessible to clinicians. In spite of the advances of recent years, 20-30% of patients diagnosed with epilepsy are not really epileptic, a fact that it is excessive and unacceptable (AU)

[Brain oscillations: pathophysiological and potentially therapeutic role in some neurological and psychiatric diseases]. / Oscilaciones cerebrales: papel fisiopatológico y posiblemente terapéutico en algunas enfermedades neurológicas y psiquiátricas.

The terms "oscillations" or "oscillatory activity" are frequently used not only to define the rhythmic fluctuations of the postsynaptic potentials of a neuronal group (local field potentials) or a cortical region (EEG, MEG), but also to indicate the rhythmic discharge pattern of action potentials from a neuron or a small group of neurons. Oscillatory activity makes possible the synchronization of different neuronal groups from nearby or distant cortical regions that participate in the same motor, sensory or cognitive task. The presence of oscillatory activity is usually associated to the existence of synchronization, but both phenomena are not necessarily always equivalent. Abnormalities of oscillatory activities or synchronization within or between different brain structures have been described in several neurological and psychiatric diseases; these abnormalities might play a relevant pathophysiological role in Parkinson's disease (and other movement disorders), schizophrenia or epilepsy. This review discusses all these aspects, with emphasis on their potential role both as a basic mechanism in brain function and as a pathophysiological substrate for some of the symptoms and signs observed in several diseases.

[Video-electroencephalography: a necessity]. / Vídeo-electroencefalografía: una necesidad.

The video-EEG is a common diagnostic tool nowadays. The technical achievements of the last decade have brought a simplification of the equipment required to obtain good quality recordings, with little more than a computer and a video camera being necessary. However, the medical and technical staff must be well trained to execute and interpret the study. It is very useful in the diagnosis of paroxysmal events, for the classification and characterization of epileptic seizures and to quantify epileptiform discharges. Due to the importance of a correct diagnosis to avoid mistreating many neurological patients, this tool should be accessible to clinicians. In spite of the advances of recent years, 20-30% of patients diagnosed with epilepsy are not really epileptic, a fact that it is excessive and unacceptable.

A suitable test for identifying high risk adult patients of moderate-severe obstructive sleep apnea syndrome.

The aim of this study was the evaluation of the usefulness of a 7-items questionnaire, Rome Questionnaire (RQ), in identifying adult patients at risk of obstructive sleep apnoea syndrome (OSAS). 136 adults (76 M, 60 F) with snoring were enrolled. Each patient underwent to an overnight polysomnography (PSG) study and the patient's bed partner answered the "RQ". RQ survey items mainly addressed the presence and frequency of snoring behaviour, breathing pauses, sore throat, oral breathing and wake time sleepiness. Of the 136 initial patients, 111 (63 M, 48 F; mean age 54.6 +/- 10.84) with a complete PSG examination were included in the study. They were divided according to apnea-hypopnea index (AHI) into two groups: group A with a primary snoring or mild OSAS (AHI < or = 15) and group B with moderate-severe OSAS (AHI > 15). The RQ final score was 25.27 +/- 16.1 for group A and 42.29 +/- 15.2 for group B, with a statistically significant (p < 0.0001) difference. Analyzing the RQ score of group B (moderate-severe OSAS) we surprisingly noticed that most of patients (66%) showed an high RQ score (> 40). No patients with moderate-severe OSAS showed a RQ score < 20 and for every point scored in the questionnaire there is an extra 1.07 (0.7%) risk of belonging to group B. Group B showed a mean body mass index (BMI) of 31.53 (+/- 4.95), significantly (p < 0.001) higher than BMI of group A (26,86 +/- 3.28) and BMI results a good predictive factor (p = 0.013) of mild-severe OSAS. In conclusion, the "RQ", together with BMI, seems to be an useful tool to make a selection of the patients at higher risk of moderate-severe OSAS, who need a prompt PSG evaluation. Our findings will require further validation in larger sample of subjects.

[Management of first epileptic seizure and status epilepticus in the emergency department]. / Manejo de la primera crisis epiléptica y del status en urgencias.

First epileptic seizure is a common reason for attending the emergency department. Its management is focused on diagnosis of the episode and on identification and treatment of the underlying cause. Occasionally, anti-epileptic treatment will be required. However, when the seizure is prolonged - a condition known as status epilepticus - it becomes a life-threatening process and requires immediate treatment. In this article, general advice and guidelines for the management of seizures and of status epilepticus in emergency departments is reviewed.

[Polysomnography in the neurology patient]. / El estudio polisomnográfico en el paciente neurológico.

The polysomnography is a standardized diagnostic tool in neurology. It is used to study sleep structure and can diagnose many sleep disorders. Since this test is not always adequately available as it is a complex test that requires a qualified team and staff, its most necessary and urgent indications should be stressed in order to thus avoid the waiting lists. In this paper we review the primary indications of the nocturnal sleep studies in the different groups of neurological disorders. We review the bibliography, selecting the papers that help to specify when the polysomnographic study would be indicated and those situations in which it may be indispensable or urgent.

El estudio polisomnográfico en el paciente neurológico / Polysomnography in the neurology patient

La polisomnografía es una herramienta diagnóstica habitual. Con ella se estudia la estructura del sueño y se pueden diagnosticar múltiples patologías del mismo. Dada su no siempre adecuada accesibilidad por ser una prueba compleja y el requerimiento de equipo y personal cualificado, es importante recalcar sus indicaciones más necesarias y urgentes para así evitar las listas de espera. En esta revisión presentamos las indicaciones principales del estudio polisomnográfico en pacientes con patología neurológica. Quiere ser una revisión bibliográfica que ayude a concretar cuándo el estudio polisomnográfico estaría indicado y algunas situaciones en las que puede ser imprescindible o urgente (AU)

The polysomnography is a standardized diagnostic tool in neurology. It is used to study sleep structure and can diagnose many sleep disorders. Since this test is not always adequately available as it is a complex test that requires a qualified team and staff, its most necessary and urgent indications should be stressed in order to thus avoid the waiting lists. In this paper we review the primary indications of the nocturnal sleep studies in the different groups of neurological disorders. We review the bibliography, selecting the papers that help to specify when the polysomnographic study would be indicated and those situations in which it may be indispensable or urgent (AU)

Manejo de la primera crisis epiléptica y del status en urgencias / Management of first epileptic seizure and status epilepticus in the emergency department

La primera crisis epiléptica es una causa frecuente de consulta en los servicios de urgencias. El manejo en urgencias se centra en el diagnóstico del episodio y en la identificación de la causa subyacente, y sólo ocasionalmente será necesario el inicio de un tratamiento antiepiléptico. Sin embargo, cuando la crisis es prolongada se convierte en una verdadera emergencia médica, el estatus epiléptico, y requiere un tratamiento inmediato. En este trabajo se revisarán las pautas generales de manejo de las crisis y del estatus epiléptico en urgencias, tanto para el diagnóstico como para el tratamiento (AU)

First epileptic seizure is a common reason for attending the emergency department. Its management is focused on diagnosis of the episode and on identification and treatment of the underlying cause. Occasionally, anti-epileptic treatment will be required. However, when the seizure is prolonged - a condition known as status epilepticus - it becomes a life-threatening process and requires immediate treatment. In this article, general advice and guidelines for the management of seizures and of status epilepticus in emergency departments is reviewed (AU)

[Classification of sleep disorders]. / Clasificación de los trastornos del sueño.

Sleep disorders are frequent processes, both as a symptom associated with other diseases and as independent disorders. However, only in the last 4 decades has Sleep medicine gained its position among the medical specialties. In fact, it was only in these years that significant advances were obtained in the study of the etiology and treatment of these disorders. Similarly, the different classifications have been evolving over the years. First, they were based upon the clinical symptom; later on, more emphasis was given to the diseases. Finally, in 2005, the new classification was once again based on the symptoms. More than 90 disorders are listed in this latest classification, and an attempt is made to include the symptoms and the diseases of sleep, as well as those in which sleep disorders are fundamental. It is essential to have a clear idea of this complete classification of sleep disorders in order to deal with these patients appropriately.

Clasificación de los trastornos del sueño / Classification of sleep disorders

Los trastornos del sueño son una patología muy frecuente tanto aislada, propia como tal, o asociada a otros trastornos. Sin embargo, es una parte de la medicina relativamente nueva, dado que ha sido en los últimos 40 años cuando se ha trabajado realmente en ella, y se han producido los avances tanto diagnósticos como terapéuticos. Las clasificaciones de estas enfermedades han ido sufriendo cierta evolución, fijándose primero en los síntomas, y luego en las enfermedades. La nueva clasificación del 2005 vuelve a basarse en los síntomas. En ella se incluyen más de 90 enfermedades del sueño, y se intentan incluir tanto los síntomas, como las enfermedades propiamente del sueño y aquellas en las que los trastornos del sueño son fundamentales. Conocer y dominar esta completa clasificación es esencial para poder manejar adecuadamente estos pacientes

Sleep disorders are frequent processes, both as a symptom associated with other diseases and as independent disorders. However, only in the last 4 decades has Sleep medicine gained its position among the medical specialties. In fact, it was only in these years that significant advances were obtained in the study of the etiology and treatment of these disorders. Similarly, the different classifications have been evolving over the years. First, they were based upon the clinical symptom; later on, more emphasis was given to the diseases. Finally, in 2005, the new classification was once again based on the symptoms. More than 90 disorders are listed in this latest classification, and an attempt is made to include the symptoms and the diseases of sleep, as well as those in which sleep disorders are fundamental. It is essential to have a clear idea of this complete classification of sleep disorders in order to deal with these patients appropriately

High-frequency oscillations during human focal seizures.

Discrete high-frequency oscillations (HFOs) in the range of 100-500 Hz have previously been recorded in human epileptic brains using depth microelectrodes. We describe for the first time similar oscillations in a cohort of unselected focal epileptic patients implanted with EEG macroelectrodes. Spectral analysis and visual inspection techniques were used to study seizures from 10 consecutive patients undergoing pre-surgical evaluation for medically refractory focal epilepsy. Four of these patients had focal seizure onset in the mesial temporal lobe, and in all 12 of their seizures, well-localized, segmental, very high frequency band (VHF: 250-500 Hz) oscillations were visually identified near the time of seizure onset from contacts in this zone. Increased high-frequency band (HF: 100-200 Hz) activity compared with the background was distinguished both visually and with spectral analysis later in the seizures of 3/4 mesial temporal patients, involving contacts in the generator region and, in one patient, areas of contralateral peri-hippocampal propagation. Three patients with well-defined neocortical seizure-onset areas also demonstrated focal HF or VHF oscillations confined to the seizure-onset channels during their eight seizures. No discrete HF or VHF activity was present in the poorly localized seizures from the remaining three patients. These results show that discrete HFOs can be recorded from human focal epileptic brain using depth macroelectrodes, and that they occur mostly in regions of primary epileptogenesis and rarely in regions of secondary spread. Absent high-frequency activity seems to indicate poor localization, whereas the presence of focal HFOs near the time of seizure onset may signify proximity to the epileptogenic focus in mesial temporal lobe and neocortical seizures. We postulate that focal HFOs recorded with depth macroelectrodes reflect the partial synchronization of very local oscillations such as those previously studied using microelectrodes, and result from interconnected small neuronal ensembles. Our finding that localized HFOs occur in varying anatomical structures and pathological conditions perhaps indicates commonality to diverse epileptogenic aetiologies.

A system for automatic artifact removal in ictal scalp EEG based on independent component analysis and Bayesian classification.

OBJECTIVE: To devise an automated system to remove artifacts from ictal scalp EEG, using independent component analysis (ICA). METHODS: A Bayesian classifier was used to determine the probability that 2s epochs of seizure segments decomposed by ICA represented EEG activity, as opposed to artifact. The classifier was trained using numerous statistical, spectral, and spatial features. The system's performance was then assessed using separate validation data. RESULTS: The classifier identified epochs representing EEG activity in the validation dataset with a sensitivity of 82.4% and a specificity of 83.3%. An ICA component was considered to represent EEG activity if the sum of the probabilities that its epochs represented EEG exceeded a threshold predetermined using the training data. Otherwise, the component represented artifact. Using this threshold on the validation set, the identification of EEG components was performed with a sensitivity of 87.6% and a specificity of 70.2%. Most misclassified components were a mixture of EEG and artifactual activity. CONCLUSIONS: The automated system successfully rejected a good proportion of artifactual components extracted by ICA, while preserving almost all EEG components. The misclassification rate was comparable to the variability observed in human classification. SIGNIFICANCE: Current ICA methods of artifact removal require a tedious visual classification of the components. The proposed system automates this process and removes simultaneously multiple types of artifacts.

Independent component analysis identifies ictal bitemporal activity in intracranial recordings at the time of unilateral discharges.

OBJECTIVE: To apply independent component analysis (ICA) in intracranial recordings to analyze interactions during temporal lobe seizures. METHODS: Seizures from 20 patients with bitemporal implantation were classified as unilateral or bilateral and analyzed with ICA. During the period preceding bilateral activity, correlation coefficients were calculated between ICA components having ictal activity during the unilateral seizure phase (early ICA components) and every channel of the original EEG. ICA components were classified as unilateral if the correlation was >0.2 exclusively with channels in one hemisphere; and bilateral if both hemispheres were involved. RESULTS: One hundred twenty-three seizures were analyzed. Thirty-two percent of visually classified unilateral seizures and 64% of bilateral seizures (during the unilateral phase) had bilateral ICA components. The proportion of early ICA components that were bilateral and the proportion of channels contralateral to the visually identified seizure with correlation higher than 0.2 with at least one early ICA component were significantly lower in seizures that stayed unilateral than in seizures that later became bilateral by visual inspection (11 and 10%, respectively, in unilateral seizures; 33 and 28% in bilateral seizures; P=0.001). CONCLUSIONS: In patients with bitemporal epilepsy, approximately 20% of the components extracted using ICA have a bitemporal distribution even at the time when the seizures are apparently unilateral. The presence of early contralateral ictal activity is more frequent and extensive in seizures that later become evidently bilateral. SIGNIFICANCE: Minimal contralateral seizure activity is present even when the discharge appears unilateral and this is more frequent in seizures which later spread to the contralateral temporal lobe.

Análisis matemáticos en el estudio de señales electroencefalográficas / Mathematical analyses in the study of electroencephalographic signals

Objetivo. Se revisan las principales técnicas matemáticas utilizadas actualmente en el estudio de las señales electroencefalográficas (EEG). Desarrollo. La introducción de los equipos digitales de registro del EEG ha permitido el desarrollo de técnicas matemáticas para su estudio. Son técnicas relativamente novedosas y en continuo desarrollo. Existen numerosas técnicas que se pueden clasificar en función de los aspectos del EEG que estudian. Entre estos aspectos destacan: creación de nuevos montajes; eliminación de artefactos; análisis en el dominio del tiempo, coherencia de fase y sincronía; estudio de fuentes; detección y predicción de crisis; superposición de actividad eléctrica y otras técnicas de neuroimagen. Han demostrado su eficacia en el estudio de las distintas áreas, pero la comparación entre ellas no siempre es sencilla. Conclusiones. El desarrollo de técnicas matemáticas en el estudio del EEG ha permitido un mejor conocimiento de la señal electroencefalográfica y, por tanto, de la actividad eléctrica cerebral, tanto en condiciones fisiológicas como en diversas patologías. Estudian aspectos muy diversos del EEG. Su continuo desarrollo permite seguir profundizando en el conocimiento del funcionamiento cerebral (AU)

Aim. The principal mathematical techniques applied to the EEG are reviewed. Development. After the introduction of digital EEG, new mathematical tools have been developed for the EEG analysis. Nowadays there are several techniques that analyse the EEG signal in different ways, getting a better understanding of the EEG: development of new montages; artifact removal; analysis in time domain, phase coherence and synchrony; source analysis; epileptic seizures detection and prediction; superposition of electrical activity and other neuroimaging techniques. Although they have demonstrated their efficacy, the comparison between them is not always easy. Conclusions. The development of mathematical tools for EEG analysis has improved the knowledge of the electric cerebral activity in normal and pathological conditions. They study many different aspects of the EEG signal. Their continuous development will produce an increase the knowledge of the normal and pathological cerebral functions (AU)

[Mathematical analyses in the study of electroencephalographic signals]. / Análisis matemáticos en el estudio de señales electroencefalográficas.

AIM: The principal mathematical techniques applied to the EEG are reviewed. DEVELOPMENT: After the introduction of digital EEG, new mathematical tools have been developed for the EEG analysis. Nowadays there are several techniques that analyse the EEG signal in different ways, getting a better understanding of the EEG: development of new montages; artifact removal; analysis in time domain, phase coherence and synchrony; source analysis; epileptic seizures detection and prediction; superposition of electrical activity and other neuroimaging techniques. Although they have demonstrated their efficacy, the comparison between them is not always easy. CONCLUSIONS: The development of mathematical tools for EEG analysis has improved the knowledge of the electric cerebral activity in normal and pathological conditions. They study many different aspects of the EEG signal. Their continuous development will produce an increase the knowledge of the normal and pathological cerebral functions.

El análisis de componentes independientes (ICA) en el estudio de señales electroencefalográficas / Independent Components Analysis (ICA) in the study of electroencephalographic signals

EI análisis de componentes independientes (lCA) descompone señales complejas en componentes estadísticamente independientes. Se incluye dentro de las técnicas de separación ciega de fuentes (BSS). Las características del electroencefalograma (EEG) lo convierten en una señal adecuada para la aplicación del ICA. En este trabajo se exponen los fundamentos del método y se revisa la literatura sobre las distintas aplicaciones del ICA en el EEG: a) eliminación de artefactos; b) análisis de grafoelementos epileptiformes, y e) análisis de crisis epilépticas. Finalmente se plantea el posible futuro del ICA en la práctica clínica. El ICA es una herramienta útil para la eliminación de artefactos sin alterar la actividad de origen cerebral en registros electroencefalográficos. Su capacidad para separar fuentes hacen que sea una herramienta útil para el estudio de descargas epilépticas. En combinación con técnicas de localización de fuentes, como el cálculo de dipolos, mejora la exactitud de la localización del foco epiléptico

Independent Component Analysis (ICA) is a mathematical tool able to separate complex signals in statistically independent components. It solves the blind source separation problem (BSS). The EEG satisfies most of the assumptions of ICA, so it may be an adequate signal for ICA for its use. In this paper we review the method and the applications of ICA in EEG. The studied applications are: a) artefacts; b) source estimation of spikes; c) analysis of seizures. Several studies have demonstrated that ICA is useful to remove artifacts from contaminated EEG records without distorting cerebral activity. It is able to decompose epileptic discharges and seizures in independent spatio-temporal components. In combination with techniques of source localisation, as dipole modelling, ICA impraves the localization of the epileptic focus. Finally, we discuss the future rale of ICA in the study of epileptic patients