Digital EEG Recordings Research Articles

Workshops (WS) Workshop 1: Electroencephalogram (EEG) WS1.1. The origin of EEG, recording techniques and quality

EEG records the electrical activity of the cerebral cortex, mainly from large pyramidal neurons close to the surface, and this activity is influenced by subcortical structures. At least 6 cm 2 of synchronised cortical activity is required to be recorded by scalp EEG. Surface electrodes are placed equidistantly over the scalp according to an international convention (10–20 System), ensuring good electrical contact, with electrode impedances <5000 ohms. Each electrode is influenced by both physiologically relevant activity and high amplitude environmental electrical noise, so pairs of electrodes are connected to differential (common-mode rejection) amplifiers to hopefully cancel out the environmental noise and record any differences between the two electrodes. Digital EEG amplifiers then use analogue-to-digital converters to translate the recorded voltage differences into numerical values, requiring an amplitude resolution of at least 12 bits (usually ≥16 bits), and with the number of measurements per second (sampling rate) at least three times the highest frequency being recorded (≥256 Hz). Filtering highlights activity that is biologically relevant, using a bandpass of 0.5–70 Hz for routine diagnostic EEG, but filtering distorts raw data and is no substitute for good technique. Digital EEG recording uses a system reference electrode separate from the 10–20 recording electrodes and stores the voltage measurements for each recording electrode relative to this system reference electrode. This allows reformatting of EEG channels and montages after the recording simply by combining any electrode pair to create the channel. At least longitudinal bipolar, transverse bipolar and referential montages should be used to read EEG. Unfortunately, EEG is commonly misinterpreted, leading to misdiagnosis. Age and state dependency dramatically influence the normal EEG, and there are many variations of normal, especially during drowsiness and sleep. ECG, careful clinical observation and video recording (routine if possible) are required throughout the recording to recognise artefacts and other important changes. For EEG to be useful, comprehensive knowledge, training and experience are required under the supervision of a skilled mentor. When in doubt, it is best to assume that background slowing is related to drowsiness/sleep, and every sharply contoured wave is an artefact or normal variant until proven otherwise.

Detection of seizure patterns with multichannel amplitude-integrated EEG and the color density spectral array in the adult neurology intensive care unit.

This study's purpose was to determine the sensitivity, false-positive and false-negative of seizure detection in adult intensive care by amplitude-integrated electroencephalography (aEEG) and color density spectral array (CDSA).30 continuous electroencephalogram (EEG) recordings were randomly performed in 3 digital EEG-recording machines, 3 specialized neurophysiologists participated in this study, underwent 4 hours of training of CDSA and aEEG, marked any epochs suspected to be seizures without access to the raw EEG. The results will be compared and analyzed with continuous EEG reading to consider sensitivity, positive or negative rate.The recordings in this study, comprised 720 hours of EEG containing a total of 435 seizures. The median sensitivity for seizure identification was 80% of CDSA and 81.3% of aEEG, Median false-positive was 4 per 24 hours of CDSA, and 2 per 24 hours of aEEG display, Median false-negative was 4 per 24 hours of CDSA, and 4 per 24 hours of aEEG display. The time spent in identification of seizures by CDSA and aEEG was much time-saving than continuous EEG-reading.In this study, both CDSA and aEEG have a higher sensitivity but lower false-positive or missed rate in the interpretation of seizure identification in adult NICU.

Quantitative EEG Tomography of Early Childhood Malnutrition.

The goal of this study is to identify the quantitative electroencephalographic (qEEG) signature of early childhood malnutrition [protein-energy malnutrition (PEM)]. To this end, archival digital EEG recordings of 108 participants in the Barbados Nutrition Study (BNS) were recovered and cleaned of artifacts (46 children who suffered an episode of PEM limited to the first year of life) and 62 healthy controls). The participants of the still ongoing BNS were initially enrolled in 1973, and EEGs for both groups were recorded in 1977–1978 (at 5–11 years). Scalp and source EEG Z-spectra (to correct for age effects) were obtained by comparison with the normative Cuban Human Brain Mapping database. Differences between both groups in the z spectra (for all electrode locations and frequency bins) were assessed by t-tests with thresholds corrected for multiple comparisons by permutation tests. Four clusters of differences were found: (a) increased theta activity (3.91–5.86 Hz) in electrodes T4, O2, Pz and in the sources of the supplementary motor area (SMA); b) decreased alpha1 (8.59–8.98 Hz) in Fronto-central electrodes and sources of widespread bilateral prefrontal are; (c) increased alpha2 (11.33–12.50 Hz) in Temporo-parietal electrodes as well as in sources in Central-parietal areas of the right hemisphere; and (d) increased beta (13.67–18.36 Hz), in T4, T5 and P4 electrodes and decreased in the sources of bilateral occipital-temporal areas. Multivariate Item Response Theory of EEGs scored visually by experts revealed a neurophysiological latent variable which indicated excessive paroxysmal and focal abnormality activity in the PEM group. A robust biomarker construction procedure based on elastic-net regressions and 1000-cross-validations was used to: (i) select stable variables and (ii) calculate the area under ROC curves (AUC). Thus, qEEG differentiate between the two nutrition groups (PEM vs Control) performing as well as visual inspection of the EEG scored by experts (AUC = 0.83). Since PEM is a global public health problem with lifelong neurodevelopmental consequences, our finding of consistent differences between PEM and controls, both in qualitative and quantitative EEG analysis, suggest that this technology may be a source of scalable and affordable biomarkers for assessing the long-term brain impact of early PEM.

F168. An EEG fingerprint of early protein-energy malnutrition

Early childhood Protein Energy Malnutrition (PEM) is an increasing worldwide phenomenon with lifelong neurodevelopmental consequences. There is thus a need for inexpensive imaging technologies to objectively identify and follow up the neural impact of malnutrition—Electroencephalography being an obvious choice. But EEG studies of PEM are scarce, performed on subjects with multiple stressors, only in the acute phase. A unique opportunity to improve these enquiries is the still ongoing Barbados Nutrition Study (BNS) which enrolled (1967–72) children with PEM during their first year of life. Under the direction of Frank Ramsey and E. Roy John, 248 digital EEG recordings were obtained (children 5–11 years) at the time that the Brain Research Lab and the Cuban Neuroscience Centre were developing quantitative EEG (qEEG; John et al., 1977). Recently, a large subsample of these digital EEGs was recovered. A unique opportunity to identify a qEEG fingerprint of early PEM has thus arisen, and which we here report. The final sample comprised 46 PEM and 62 control recordings (1 min resting state, eyes-closed,19 electrodes 10/20 system, sampling 100 Hz). Qualitative EEG was evaluated using a Likert-type scale. Multivariate Item Response Theory identified a neurophysiological state (NS) as a single latent variable explaining 0.88 of sample variance. qEEG evaluation at the electrodes (topography) consisted in calculating the log-power spectrum both at the scalp electrodes and sources and computing the z transform with regard to the Cuban normative database. Quantitative tomographic EEG (qEEGt) was carried out with CNEURO’s VARETA source analysis procedure based upon an MNI probabilistic template—necessary since MRIs where not available at that time. Multivariate permutation tests (N = 1000) were applied to t-tests in order to assess differences between groups. Qualitative analysis revealed highly significant changes in the latent variable (NS) with the PEM group showing excessive slow-wave, paroxysmal and focal abnormality activity, with a statistically significant effect for groups (p < 0.00001). qEEG (topographic) revealed (PEM) an increment of slow activities (<5 Hz) in centro-parietal electrodes and a decrease of alpha in fronto-central electrodes around 8.98 Hz as well as a significant increase of fast activity >15.2 Hz. qEEGT analysis: the PEM group, showed a significant increment in source power at lower frequencies (<5 Hz) and a decrease of power in alpha (8.9 Hz) in frontal region. The consistent differences in qEEG and qEEGt values between PEM and controls suggest they may be affordable biomarkers for the long-term actual brain impact of early childhood PEM. Excess slow-waves activity and decreased alpha activity in PEM children, may be a qEEG fingerprint of early PEM predicting which is correlated with many types of neuropathology, learning and performance difficulties.

S18-1. Progress in EEG analysis for epilepsy and the outlook for the future

Epileptic seizures are the result of excessive and abnormal neuronal activities in the cortex of the cerebrum. Hans Berger (German) initially recorded EEG activities of alpha and beta waves with in 1924. Gibbs, Davis and Lennox described interictal spikes and 3 Hz spike-and-wave pattern on absence seizures in 1935. Jasper and Penfield clarified the epileptic focus in a patient with partial epilepsy using EEG. From 1950s, scalp EEG has been widely used in clinical field of epilepsy. Intracranial EEG was also used for presurgical evaluations. The clinical interpretations of EEG were mostly focused on the timings of occurrence, distributions and shapes of the EEG activities from 1 to 30 Hz. With the dawning of digital EEG recording and computer analysis, high-frequency oscillations (HFOs), which are the activities from 100 to 500 Hz, came to be analyzed. The HFOs are found seizure onset zone or epileptogenic zones on cortices during ictal and interictal EEG activities. Inflaslow oscillations (

Evaluation of the first seizure patient: Key points in the history and physical examination

PurposeThis review will present the history and physical examination as the launching point of the first seizure evaluation, from the initial characterization of the event, to the exclusion of alternative diagnoses, and then to the determination of specific acute or remote causes. Clinical features that may distinguish seizures from alternative diagnoses are discussed in detail, followed by a discussion of acute and remote first seizure etiologies. MethodsThis review article is based on a discretionary selection of English language articles retrieved by a literature search in the PubMed database, and the authors’ clinical experience. ResultsThe first seizure is a dramatic event with often profound implications for patients and family members. The initial clinical evaluation focuses on an accurate description of the spell to confirm the diagnosis, along with careful scrutiny for previously unrecognized seizures that would change the diagnosis more definitively to one of epilepsy. The first seizure evaluation rests primarily on the clinical history, and to a lesser extent, the physical examination. ConclusionsEven in the era of digital EEG recording and neuroimaging, the initial clinical evaluation remains essential for the diagnosis, treatment, and prognostication of the first seizure.

American Clinical Neurophysiology Society Guideline 4: Recording Clinical EEG on Digital Media.

Digital EEG recording systems are now widely available and relatively inexpensive. They offer multiple advantages over previous analog/paper systems, such as higher fidelity recording, signal postprocessing, automated detection, and efficient data storage. This document provides guidance for the creation of digital EEG recordings including (1) documentation of patient information, (2) notation of information during the recording, (3) digital signal acquisition parameters during the recording, (4) storage of digital information, and (5) display of digital EEG signals.

Valoración del envejecimiento a partir de la conectividad funcional cerebral estimada mediante medidas de sincronización electroencefalográficas

En este trabajo estudiamos el envejecimiento cerebral fisiológico a partir del análisis de la conectividad electroencefalográfica (EEG) funcional entre distintas zonas corticales en dos grupos de sujetos sanos entre 50-65 años y entre 66-80 años. Para ello, se realizaron (en reposo y ojos cerrados) registros EEG digitales monopolares (256 Hz de frecuencia de muestreo) referenciados al promedio de 16 canales/electrodos (6-frontales, 4-temporales, 2-centrales, 2-parietales, 2-occipitales).Estimamos la conectividad entre canales mediante la función de coherencia en las bandas de frecuencia delta/theta/alfa/beta, y mediante un índice (L) de sincronización no lineal generalizada. Analizamos la conectividad individual entre todos los pares posibles de canales y la conectividad global de cada canal con el resto. Los resultados muestran que determinadas interdependencias individuales medidas por el índice L y por la coherencia en banda-delta, decrecen con la edad, especialmente para las conexiones centro-temporales-occipitales. Además, se observa un decrecimiento lineal significativo con la edad de los índices de interdependencia señalados,especialmente para las parejas y promedios individuales de las zonas señaladas. También las interdependencias globales, especialmente las de tipo no lineal, de ciertas zonas centro-laterales y posteriores declinan con la edad. Concluimos que, medidas individuales y globales de conectividad funcional EEG entre determinadas áreas corticales pueden ayudar a valorar objetivamente el envejecimiento neurofisiológico.

EEG guidelines in the diagnosis of brain death

In France, for the determination and diagnostic validation of brain death the law requires either two EEG recordings separated by a 4-hour observation period, both showing electrocerebral inactivity; or cerebral angiography examination. Since EEG is available in most hospitals and clinics, it is often used in this indication, at the patient's bedside, especially in the context of organ donation. However, very precise methodology must be followed. The last French guidelines date back to 1989, before the development of digital EEG recording. We present the new guidelines from the Société de Neurophysiologie Clinique de Langue Française. Electrocerebral inactivity may be confirmed when a 30-minute good quality EEG recording shows complete electrocerebral silence, defined as no cerebral activity greater than 2 uV, having first ruled out the possible influence of sedative drugs, metabolic disorders or hypothermia. In the presence of sedative drugs, CT brain angiography will be the gold standard test for this diagnosis. In the newborn, the utmost caution is indicated since electrocerebral inactivity can be observed in the absence of cerebral death. In the infant, the criterion for the observation period to be respected between both EEG recordings needs to be more clearly refined.

Assessment of aging by cortical functional connectivity estimated through synchronization electroencephalographic measurements

This work was aimed to study the physiological cerebral aging from the analysis of functional electroencephalographic (EEG) connectivity between different cortical areas in two groups of healthy subjects between 50-65 years and between 66-80 years. With this purpose, digital monopolar EEG recordings were carried out at rest and closed eyes, taking as sampling rate, 256 Hz and as reference, the average of the 16 channels recorded (6-frontals, 4-temporals, 2-centrals, 2-parietal, 2-occipital). The functional cortical connectivity was estimated from the interdependence between channels using the coherence function in the frequency bands delta/theta/alpha/beta, and an index (L) of nonlinear generalized synchronization. The pairwise connectivity between all possible channels and a global connectivity between each channel and all others was computed. The results show that certain local interdependencies measured by the index L and by the delta band coherence, decreased with age; these were especially significant for the temporal-occipital-central connections. Moreover, a significant linear decrease with age of the interdependence indices aforementioned for the pair and local averages was observed. Also global interdependencies, especially those of nonlinear type, for certain central-lateral and posterior areas, decline with age. It is concludes that individual and global measures of EEG functional connectivity between certain brain areas can help to objectively evaluate the neurophysiological aging.

Assessment of aging by cortical functional connectivity estimated through synchronization electroencephalographic measurements

This work was aimed to study the physiological cerebral aging from the analysis of functional electroencephalographic (EEG) connectivity between different cortical areas in two groups of healthy subjects between 50-65 years and between 66-80 years. With this purpose, digital monopolar EEG recordings were carried out at rest and closed eyes, taking as sampling rate, 256 Hz and as reference, the average of the 16 channels recorded (6-frontals, 4-temporals, 2-centrals, 2-parietal, 2-occipital). The functional cortical connectivity was estimated from the interdependence between channels using the coherence function in the frequency bands delta/theta/alpha/beta, and an index (L) of nonlinear generalized synchronization. The pairwise connectivity between all possible channels and a global connectivity between each channel and all others was computed. The results show that certain local interdependencies measured by the index L and by the delta band coherence, decreased with age; these were especially significant for the temporal-occipital-central connections. Moreover, a significant linear decrease with age of the interdependence indices aforementioned for the pair and local averages was observed. Also global interdependencies, especially those of nonlinear type, for certain central-lateral and posterior areas, decline with age. It is concludes that individual and global measures of EEG functional connectivity between certain brain areas can help to objectively evaluate the neurophysiological aging.

Cognitive and neuropsychiatric correlates of EEG dynamic complexity in patients with Alzheimer's disease

This study assessed the utility of multiscale entropy (MSE), a complexity analysis of biological signals, to identify changes in dynamics of surface electroencephalogram (EEG) in patients with Alzheimer's disease (AD) that was correlated to cognitive and behavioral dysfunction. A total of 108 AD patients were recruited and their digital EEG recordings were analyzed using MSE methods. We investigate the appropriate parameters and time scale factors for MSE calculation from EEG signals. We then assessed the within-subject consistency of MSE measures in different EEG epochs and correlations of MSE measures to cognitive and neuropsychiatric symptoms of AD patients. Increased severity of AD was associated with decreased MSE complexity as measured by short-time scales, and with increased MSE complexity as measured by long-time scales. MSE complexity in EEGs of the temporal and occipitoparietal electrodes correlated significantly with cognitive function. MSE complexity of EEGs in various brain areas was also correlated to subdomains of neuropsychiatric symptoms. MSE analysis revealed abnormal EEG complexity across short- and long-time scales that were correlated to cognitive and neuropsychiatric assessments. The MSE-based EEG complexity analysis may provide a simple and cost-effective method to quantify the severity of cognitive and neuropsychiatric symptoms in AD patients.

P.1.b.00l Digital EEG recording during hallucinatory behaviour in a sample of patients with paranoid schizophrenia

Cet article interroge le statut singulier de l’hallucination dans la clinique infantile. Effet de trauma, phénomène xénopathique ou expression ayant trait au mode hallucinatoire qui régit le fonctionnement infantile, l’hallucination chez l’enfant intervient tel un phénomène d’interface entre des expressions psychopathologiques et le développement psychoaffectif ordinaire. En raison de la fréquence relative des cas observés et de l’importance des problèmes diagnostiques qu’elle soulève, la valeur psychopathologique des hallucinations infantiles constitue un champ clinique des plus controversés. L’hallucination chez l’enfant, en tant que symptôme de premier rang pour le diagnostic de la schizophrénie infantile n’a pas pour autant valeur pathognomonique pour cette affection.L’auteur dégage quelques éléments cliniques et psychopathologiques fondamentaux concernant le phénomène de l’hallucination infantile, tout en distinguant l’hallucination en tant que formation psychopathologique du mode hallucinatoire de la satisfaction hallucinatoire du désir et de son échec, qui sont à la base de l’activité psychique organisatrice du rapport à la réalité. Dans un deuxième temps, la problématique du statut psychopathologique de l’hallucination est abordée à partir d’un fragment clinique extrait de la cure d’une fillette de neuf ans. Les hallucinations multi-sensorielles de cette patiente seront discutées à la lumière des éléments métapsychologiques de la théorie freudienne.L’inscription des hallucinations de cette fillette dans le champ de la clinique du trauma plutôt que dans le champ de la schizophrénie infantile est le résultat d’une l’analyse des éléments à la fois cliniques, transférentiels et psychopathologiques.La notion freudienne de la trace verbale et ses destins psychiques est à l’épicentre de la discussion. La réactivation hallucinatoire de la trace verbale constitue la voie pour la construction du rapport à la réalité. Suivant l’hypothèse de ce texte, c’est en hallucinant les traces verbales que l’être humain apprend à parler, dans la mesure où l’activité hallucinatoire des traces mnésiques enracine les marques élémentaires de la langue au corps, le faisant advenir comme corps libidinal.Cette réflexion est traversée par un souci diagnostique concernant la problématique des hallucinations dans la clinique infantile. Les conclusions apportées, même si elles ne peuvent être que spécifiques au cas clinique rapporté, constituent un apport plus général pour l’abord du phénomène des hallucinations dans la clinique infantile.This article explores the particular status of hallucinations in paediatric psychiatry. Hallucination in children, whether it is an effect of trauma, a xenopathological phenomenon, or belongs to the hallucinatory functioning of children, acts as a kind of interface between psychopathological manifestations and the normal course of normal psycho-affective development. Because of the relative frequency of observed cases and the considerable difficulties raised for the diagnostic process, the psychopathological value of hallucination in children is a highly controversial clinical field. Yet hallucinations in children, one of the main symptoms for the diagnosis of childhood schizophrenia, do not possess pathognomonic value for this condition.The article identifies certain fundamental clinical and psychopathological elements relating to hallucination in children, while at the same time distinguishing hallucination as a psychopathological formation from the hallucinatory mode of functioning procuring the satisfaction of a desire, and the failure thereof, which underpin the psychic activity organising relationships with reality. In a second section, the article uses a clinical fragment from the cure of a girl aged nine to broach the question of the psychopathological status of hallucination. The multi-sensory hallucinations of this patient are discussed in the light of meta-psychological elements in Freudian theory.The analysis of clinical, transference and psychopathological elements enables us to position this patient's hallucinations in the clinical field of trauma rather than in that of childhood schizophrenia.Thus at the epicentre of our discussion is the Freudian notion of the verbal trace and its psychic outcome. The hallucinatory reactivation of the verbal trace is the pathway for the construction of a relationship with reality. In line with the hypothesis set out by Freud, it is by “hallucinating” verbal traces that human beings learn to speak, since the hallucinatory activity of mnemonic traces fixes the elementary marks of language in the body, enabling it to become the libidinal body.This article focuses particularly on the issue of diagnosis in presence of hallucinations in children. The conclusions offered, although necessarily specific to the reported case, do have more general interest, suggesting ways in which to approach the phenomenon of hallucination in children.

Engineering Aspects of the Quantified Amplitude-Integrated Electroencephalogram in Neonatal Cerebral Monitoring

Amplitude-integrated electroencephalography (aEEG) is used for determination of severity of hypoxic-ischemic encephalopathy and eligibility for hypothermia therapy in infants. We evaluate susceptibility of the aEEG to machine differences, impedance mismatch, electrode placement, and interelectrode distance in preparation for further clinical studies. Frequency-response curves were obtained from manufacturers of aEEG systems. The mean of the quantified aEEG and the median lower border of amplitude were derived from digital EEG recordings. Impedance effects were evaluated by inserting resistors ranging from 1 kOmega to1 MOmega into inputs G1/G2 while recording from a looped-signal generator. Interelectrode distance effects were evaluated from simultaneous recordings from electrodes placed at 5% to 30% of the preauricular notch distance from a healthy human subject. Electrode location effects were evaluated by comparing Q-aEEG from C3-C4 versus P3-P4 from 10 term infants. Frequency-response curves differed up to 20 dB for particular frequencies. Impedance mismatch distorted EEG and aEEG, but did not significantly change Q-aEEG. Increasing interelectrode distances significantly increased Q-aEEG. Central Q-aEEG values were significantly higher than parietal. Comparisons of aEEG must carefully account for differences in machines, interelectrode distances, and electrode locations. Q-aEEG may offer a rigorous method of evaluating hypoxic-ischemic encephalopathy.

Influence of filters in the detrended fluctuation analysis of digital electroencephalographic data

The technique named detrended fluctuation analysis (DFA) has been used to reveal the presence of long-range temporal correlations (LRTC) and scaling behavior (SB) in electroencephalographic (EEG) recordings. The occurrence of these phenomena seems to be a salient characteristic of the healthy human brain and alterations in different pathologies has been described. Here we show how the filtering stages implemented in the systems for digital EEG influence the estimation of the DFA parameters used to characterize the brain signals. In consequence, we conclude that it is important to consider these filtering effects before interpreting the results obtained from digital EEG recordings.

Effect of carbon dioxide on background cerebral electrical activity and fractional oxygen extraction in very low birth weight infants just after birth

Decreased arterial carbon dioxide tension (PaCO2) results in decreased cerebral blood flow, which is associated with diminished cerebral electrical activity. In such a situation, cerebral fractional oxygen extraction (CFOE) would be expected to increase to preserve cerebral oxygen delivery. This study aimed to determine whether changes in blood gases in infants less than 30 wk' gestation were associated with changes in background electroencephalograms (EEG) and CFOE. Thirty-two very low birth weight infants were studied daily for the first three days after birth. Digital EEG recordings were performed for 75 min each day. CFOE, mean blood pressure and arterial blood gases were measured midway through each recording. EEG was analysed by (a) spectral analysis and (b) manual calculation of interburst interval. Blood pressure, pH and PaCO2 did not have any effect on the EEG. On day one, only PaCO2 showed a relationship with the relative power of the delta frequency band (0.5-3.5 Hz) and the interburst interval. The relative power of the delta band remained within normal limits when PaCO2 was between 24 and 55 mmHg on day one. There was a negative association between PaCO2 and CFOE. The associations between PaCO2 and EEG measurements were strongest on day one, weaker on day two, and absent on day three. The slowing of EEG and increased CFOE at lower levels of PaCO2 are likely to be due to decreased cerebral oxygen delivery induced by hypocarbia. When PaCO2 was higher, there was suppression of the EEG.

Spectral Analysis of Electroencephalography in Premature Newborn Infants: Normal Ranges

Continuous EEG monitoring has not been used widely in neonatal intensive care, especially in the care of extremely premature infants, probably in part because of a lack of a reliable quantitative method. The purpose of this study was to quantify the EEG of the very premature infants just after birth by using spectral analysis and to describe the characteristics of the spectral signal when infants were clinically stable. Digital EEG recordings were performed on 53 infants who were < or =30 wk gestation for 75 min each day during the first 4 d after birth. Artefact was rejected manually after visual inspection of trace. The EEG was analyzed by manual measurement of interburst interval and automatically by spectral analysis using Fast Fourier Transformation. Spectral analysis generated the normal ranges of the relative power of the delta (0.5-3.5 Hz), theta (4-7.5 Hz), alpha (8-12.5 Hz), and beta (13-30 Hz) frequency bands, spectral edge frequency, and symmetry. The median (range) relative power of the delta band increased significantly from 68% (62-76%) on day 1 to 81% (72-89%) on day 4 (p=0.001). The interburst intervals became progressively shorter between days 1 [14s (10-25)] and 3 [8s (6-12)]; there were no significant differences between days 3 and 4. The relative power of the delta band seemed to be the most useful and repeatable spectral measurement for continuous long-term monitoring. However, automatic artefact rejection software needs to be developed before continuous quantitative EEG monitoring can be used in the neonatal intensive care environment.

Cognitive tasks augment gamma EEG power

Objective: Gamma EEG oscillations are low amplitude rhythms in the 30–100 Hz range that correlate with cognitive task execution. They are usually reported using time-locked averaging of EEG during repetitive tasks. We tested the hypothesis that continuous gamma EEG would be measurable during mental tasks. Methods: We investigated sustained human gamma EEG oscillations induced by 8 cognitive tasks (Visual Checkerboard, Expectancy, Reading, Subtraction, Music, Expectancy, Word learning, Word recall, and a Video Segment) in 20 subjects using standard digital EEG recording and power spectral analysis. Results: All of the cognitive tasks augmented gamma power relative to a control condition (eyes open watching a blank computer screen). This enhancement was statistically significant at more than one scalp site for all tasks except checkerboard. The Expectancy, Learning, Reading and Subtraction tasks expressed the most impressive gamma response, up to 5 fold above the control condition and there was some task-related specificity of the distribution of increased gamma power, especially in posterior cortex with visual tasks. Conclusions: Widespread gamma activation of cortical EEG can easily be demonstrated during mental activity. Significance: These results establish the feasibility of measuring high frequency EEG rhythms with trans-cranial recordings, demonstrate that sustained gamma EEG activity correlates with mentation, and provides evidence consistent with the temporal binding model.

Artifact correction of the ongoing EEG using spatial filters based on artifact and brain signal topographies.

Review and analysis of continuous EEG recordings may be impeded by physiological artifacts such as blinks, eye movements, or cardiac activity. Spatial filters based on artifact and brain signal topographies can remove artifacts completely without distortion of relevant brain activity. The authors describe the basic principle of artifact correction by spatial filtering and they review different approaches to estimate artifact and brain signal topographies. The main focus is on the preselection approach, which is fast enough to be applied while paging through the segments of a digital EEG recording. Examples of real EEG segments, containing epileptic seizure activity or interictal spikes contaminated by artifacts, show that spatial filtering by preselection can be a useful tool during EEG review. Advantages and disadvantages of the different spatial filter approaches are discussed.

Monitorización del daño cerebral en pacientes con traumatismo craneoencefálico

Early detection of impending cerebral ischemia in comatose patients is most important to avoid secondary insults to the injured brain. Whilst the computer tomography scan provides a static picture primarily concerned with details of structure, the electroencephalogram (EEG) is the objective source par excellence of information about brain function. The EEG represents the only biological activity suitable for continuous non-invasive monitoring of brain function. In this context, the cerebral function monitor (CFM) of Maynard and Prior (1969) provides a compressed array of amplitude variations and has benefited many critical patients. Among the invasive methods, direct monitoring of cerebral white matter oxygenation (tissular pressure of oxygen) is a promising new technique that has attracted considerable interest over the past four years. Recent studies on multimodal hemodynamic monitoring (intracranial pressure, cerebral perfusion pressure, PtiO2), place this latter technique as a primary basis for management decisions in the ICUs. We have studied four young injured patients, to compare early digital EEG recordings with tissular pressure of oxygen data. In general, there was agreement between EEG findings and tissular pressure of oxygen levels. The EEG helped with urgent data, though barbiturate therapy interfered in two cases.