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PubMed1995

On the dimensionality of sleep-EEG data. Using chaos mathematics and a systematic variation of the parameters of the Corex program to determine the correlation exponents of sleep EEG segments.

Sleep-EEG data of 16 healthy subjects, classified according to the Rechtschaffen and Kales criteria, were taken to determine the correlation exponent (CE) or dimensionality (D2) of the data using the Corex program. We tested the applicability of this program to the analysis of sleep-EEG data changing systematically the embedding dimension (ED), the time lag (tau), the number of involved pairs of vectors and the EEG segment by split half. We could confirm the results of other authors according to which the complexity of the EEG signal decreases from stage 'awake, eyes closed' to sleep stages 1, 2, 3 and 4. The differences between the various sleep stages were significant. Stage REM could be differentiated from every stage but stage 1. The most important finding of our study was that the absolute value of the dimensionality depends on almost all the parameters tested: with increasing tau up to tau = 200 the CE increases, which means a 1.56-second shift. A higher number of pairs is needed when the signal is more complex. The ED is selected well between 6 and 11, that means reasonably higher or close to the dimensionalities for that purpose as presented in the literature. Different segments of one sleep stage in 1 subject led to different CE values, thus demonstrating that the EEG signal is not stationary over a segment of 2 min time. Although using chaos mathematics seems to be a useful tool in analyzing EEG data to explore their complexity, we could demonstrate the urgent need of calibrations and conventions to be able to interpret the absolute values.

Adult↗

PubMed1979

Prognostic value of EEG in acute vascular aphasia: a long term clinical-EEG study of 53 patients.

A group of 53 patients rendered acutely aphasic by occlusive cerebrovascular disease were studied by serial EEG's, repeated neurologic examinations and speech evaluations (Porch Index of Communicative Ability) over a period of eight to twenty-four months, in order to correlate EEG findings with the degree of language disorder and prognosis for language recovery. Normal and mildly abnormal EEG's, posterior slow foci, focal slowing of semirhythmic type and higher alpha frequencies over the intact hemisphere correlated with good language recovery. In the majority of the patients, the curves of "EEG Improvement" and "Language Recovery" closely paralleled each other. These data indicate that the EEG is of prognostic value as to recovery from aphasia in patients suffering from acute occlusive cerebrovascular disease. Despite the advent of newer diagnostic tests, such as CAT scan, which has established its value in evaluation of the anatomy of aphasia, (9) EEG remains to be useful as a tool that could predict the outcome of aphasia in stroke patients.

Adult↗

PubMed1986

The activating effect of sleep EEGs in epileptic patients with epileptic activity in their waking EEGs.

A sleep EEG was recorded in 44 patients whose waking EEG showed epileptic activity. The time in seconds in which one epileptic discharge occurred was determined. Considering the waking and sleep EEGs together one epileptic discharge occurred every 7.8 seconds. Focal epileptic activity was recorded nearly twice as frequently (1 paroxysm every 4.6 sec.), as generalized activity (1 paroxysm every 9.8 sec.) or generalized activity with lateral emphasis (1 paroxysm every 8.8 sec.). Considering the sleep and waking EEGs separately it was found that on average more epileptic activity occurred in sleep than in the waking EEG (6.4 vs. 10.8 sec.). There was no difference between generalized (8.9 vs. 13.5 sec.), generalized activity with lateral emphasis (7.7 vs. 12.9 sec.) and focal activity (3.9 vs. 7.6 sec.). Comparing, however, the frequency of epileptic activity in each individual patient during wakefulness and sleep it was seen that during sleep more activity was found in only 56.8% of the patients. If a difference of 3 seconds is considered to be due to chance, then more epileptic activity was found in 34.1% of the patients during sleep and in 24.5% during wakefulness. Thus, the sleep EEG by no means always activates epileptic activity.

Adolescent↗

PubMed1986

[Neurologic characteristics of patients with flat EEG's and EEG's with predominant low-frequency beta activity].

The authors analyzed clinical manifestations and reactive changes in the EEG in response to eye opening and light flickering in 3 groups of patients selected according to the parameters of baseline EEGs: Group I (control) (n = 20) was characterised by normal EEG; Group II (n = 50) by domination in the EEG of beta-activity of low frequency; Group III (49 patients) by a "flat" curve. It was found that micro-symptoms of organic lesion of the CNS were observed in 15% of the Group I patients, in 36% of the Group II patients, and in 61.2% of Group III patients. In Group II neurotic and neurosis-like manifestations of a hysterical type were observed in 34% of the patients while 38% of the patients in Group III presented anxiety-depressive states. The groups studied also showed significant differences in reactive shifts in the EEG. A scheme of identification of different EEG-syndrome complexes may prove useful in clinical electroencephalography.

Beta Rhythm↗

PubMed1978

[Centralized system for EEG-diagnosis and EEG-monitoring in a neurologic intensive care unit (author's transl)].

A centralized EEG system installed in a neurologic intensive care unit is described. It is the first step to a computerized EEG monitoring which on the basis of conventional EEG recordings already permits a "brain monitoring" to some extent. It consists of a system for total EEG diagnosis which is connected with a central EEG laboratory via long-distance transmission lines, and of a system for EEG-monitoring which is part of the general beside monitor system. The possibilities of this system are demonstrated in monitoring of patients with epileptic seizures.

Aged↗

PubMed1982

Pharmaco-EEG study of 6-azamianserin (ORG 3770): dissociation of EEG and pharmacologic predictors of antidepressant activity.

The effects of a single oral dose of 6-azamianserin (2 mg) were compared to those of mianserin (6 mg), flurazepam (10 mg), and placebo in 11 healthy male volunteers, in a crossover design. Quantitative EEG, heart rate, blood pressure, task performance, and subjective state were measured. EEG and behavioral measures distinguished the substances from placebo. 6-Azamianserin was similar to mianserin in type and duration of effects. In a separate study in 12 volunteers, 0.5 and 1.0 mg of the (+) and (-) enantiomers of 6-azamianserin elicited dose-related EEG and behavioral effects, distinguishable from placebo. These effects were similar to those elicited by racemic 6-azamianserin and mianserin. Clinical trials of 6-azamianserin in depressed patients, particularly the elderly and those with cardiovascular disease, are warranted. Dosages selected should be one-third those of mianserin. The stereospecific properties of the enantiomers in preclinical tests predict that any clinical 'antidepressant' activity will reside in the (+) isomer only, while the pharmaco-EEG trials predict that both enantiomers will be clinically 'antidepressant'. Clinical testing of the isomers, particularly the (-) isomer, is indicated as a test of the predictive value of pharmacologic and pharmaco-EEG models of clinical antidepressant activity.

Adult↗

PubMed1982

A double-blind investigation of the relationship between seizure activity and the sleep EEG following EEG biofeedback training.

The sleep EEGs of eight medically refractory epileptic patients were examined as part of a double-blind, ABA crossover study designed to determine the effectiveness of EEG biofeedback for the control of seizures. The patients were initially reinforced for one of three EEG criteria recorded from electrodes placed over sensorimotor cortex: (a) suppression of 3- to 7-Hz activity, (b) enhancement of 12- to 15-Hz activity, or (c) simultaneous suppression of 3- to 7-Hz and enhancement of 11- to 19-Hz activity. Reinforcement contingencies were reversed during the second or B phase, and then reinstated in their original form during the final A' phase. All-night polysomnographic recordings were obtained at the end of each conditioning phase and were subjected to both visual and computer-based power spectral analyses. Four of the patients showed changes in their nocturnal paroxysmal activity that were either partially or totally consistent with the ABA' contingencies of the study. The spectral data proved difficult to interpret, though two trends emerged from the analyses. Decreases in nocturnal 4- to 7-Hz activity were correlated with decreases in seizure activity, and increases in 8- to 11-Hz activity were correlated with decreases in seizure activity. These findings were shown to strengthen the hypothesis that EEG biofeedback may produce changes in the sleep EEG that are related to seizure incidence.

Adolescent↗

PubMed1995

EEG reactivity and EEG activity in never-treated acute schizophrenics, measured with spectral parameters and dimensional complexity.

Our approaches to the use of EEG studies for the understanding of the pathogenesis of schizophrenic symptoms are presented. The basic assumptions of a heuristic and multifactorial model of the psychobiological brain mechanisms underlying the organization of normal behavior is described and used in order to formulate and test hypotheses about the pathogenesis of schizophrenic behavior using EEG measures. Results from our studies on EEG activity and EEG reactivity (= EEG components of a memory-driven, adaptive, non-unitary orienting response) as analyzed with spectral parameters and "chaotic" dimensionality (correlation dimension) are summarized. Both analysis procedures showed a deviant brain functional organization in never-treated first-episode schizophrenia which, within the framework of the model, suggests as common denominator for the pathogenesis of the symptoms a deviation of working memory, the nature of which is functional and not structural.

Acute Disease↗

PubMed1975

An EEG simulator-a means of objective clinical interpretation of EEG.

In 1969 Zetterberg presented a method for describing the spectral properties of an EEG signal, starting from the assumption that the signal is essentially stationary during the analysis epoch. The method involves determination of the parameters for a model consisting of a lenear filter with the ability to produce a signal with the same spectral properties as the EEG signal. Zetterberg and Ahlin described in 1975 an analogue simulator based on this model theory. With this simulator it is possible to reproduce practically all types of stationary, as well as a number of non-stationary, EEG signals. We have used this simulator to demonstrate in an illustrative manner the relation between the properties of a signal in the spectral domain and in the time domain. We have also endeavoured to anser the question: if one starts from the frequency spectrum, what does the EEG signal corresponding to this spectrum look like? We also draw attention to the usefulness of the simulator in connection with training and as an instrument for testing computer and other systems of EEG analysis.

Computers↗

PubMed1979

Hippocampal EEG and behaviour in dog. III. Hippocampal EEG correlates of stimulus-response tasks and of sexual behaviour.

A dog was trained to perform a spatial sound discrimination. The hippocampal EEG correlates and the movement correlates of correct trials were compared with those of incorrect trials and of 'pressings in between'. Correct and wrong responses on a place learning task were compared both with respect to the hippocampal EEG correlates and to the motor behaviour. Where significant differences in EEG correlates were found, the motor behaviour differed significantly as well. The same was found for 2 behavioral states with different motor behavioural qualities which occurred during copulation. The data support the hypothesis that the spectral properties of the hippocampal EEG reflect in a predictable but non-specific way the intensity of motor behaviour. They question the postulated correlations between hippocampal EEG and 'internal processes', on the ground that unambiguous experimental verification of such hypothesis appears to be very difficult.

Animals↗

PubMed1983

Correlating EEG and IQ: a new look at an old problem using computerized EEG parameters.

Explorations of the relationship between EEG activity and scores of tests of intelligence have a long history. Results have been rather discrepant and several explanations can be offered for this. Almost all previous studies relied on parameters derived from a visual rather than a computerized analysis of the EEG. Here broad band spectral parameters were mainly used, and in addition the frequency of the dominant peak (at Pz, O1 and O2) between 6.5 and 14.0 Hz. All EEG parameters were standardized for age, as were tests of intelligence. Correlations of EEG with IQ were computed separately for a group of normal and a group of mildly retarded children. As postulated in advance, correlations were substantially higher for the retarded groups. Even more remarkable than the size of the correlations found was their pattern, associated with an interesting interpretation: the sign of the larger correlations was such that children developmentally more advanced in their EEG parameters had on the average higher IQ scores. Moreover, correlations were large for those frequency bands, and to a lesser degree for those derivations where we found a high developmental relevance in a previous investigation for the age range considered. Some disappointing or even discrepant results in earlier studies can be explained in the light of the results given here.

Brain↗

PubMed1987

Elimination of EKG artifacts from EEG records: a new method of non-cephalic referential EEG recording.

A new method for eliminating EKG artifacts from EEGs was reported. Based on the simultaneously recorded EEGs and EKG, the procedure consisted of 4 steps: synchronized partition of the raw EEG record into segments with respect to the QRS complex of the EKG, averaging of the segments time-locked to EKG, repetition of the average artifact synchronized to EKG and subtraction of the estimate of the artifacts from the raw data. This method enabled the elimination of EKG artifacts from EEGs recorded by using the chin or the hand electrode as a reference. Features of the proposed method include: all signals are processed in digital instead of analogue form, the average EKG wave form is computed throughout the subtraction part of the recording instead of being computed only before the subtraction starts, in case of an on-line algorithm, the average EKG wave form is always updated to the point immediately preceding the real time of EKG subtraction, and by using the recursive form of exponential weighted averaging equation, the average EKG wave form can adapt appropriately to a change of the artifact wave form. By the high speed implementation of the procedure, the processed data of multi-channel EEGs can be obtained on-line with a delay of only 200 msec.

Adult↗

PubMed1992

Long-term EEG-video-audio monitoring: computer detection of focal EEG seizure patterns.

Twelve individuals with medically refractory partial seizures had undergone EEG-video-audio (EVA) monitoring over 1-15 (mean 10.5) days. We selectively reexamined available 15-channel EEGs (video-cassettes) totaling 461 h and containing 253 EEG focal seizures. Computer analysis (CA) of these bipolar records was performed using a mimetic method of seizure detection at 6 successive computer settings. We determined the computer parameters at which this method correctly detected a reasonably large percentage of seizures (81.42%) while generating an acceptable rate of false positive results (5.38/h). These parameters were adopted as the default setting for identifying focal EEG seizure patterns in all subsequent long-term bipolar scalp and sphenoidal recordings. Factors hindering or facilitating automatic seizure identification are discussed. It is concluded that on-line computer detection of focal EEG seizure patterns by this method offers a satisfactory alternative to and represents a distinct improvement over the extremely time consuming and fatiguing off-line fast visual review (FVR). Combining CA with seizure signaling (SS) by the patients and other observers increased the correct detections to 85.38% CA is best used in conjunction with SS.

Adolescent↗

PubMed1989

Haloperidol pretreatment unmasks the kappa opioid effects of U-50, 488H on cortical EEG and EEG power spectra in rats.

Adult female Sprague-Dawley rats were implanted with chronic cortical EEG electrodes and intravenous cannulae. U-50, 488H injection (5.0 mg/kg) produced initial EEG desynchrony and EEG spectral power that was mainly distributed over the zero to 10 Hz range, including a relatively small spectral peak in the 4-6 Hz band. In contrast, following haloperidol pretreatment (0.1 mg/kg), U-50, 488H injection produced high-voltage EEG bursts and a predominant EEG spectral peak in the 4-6 Hz band. These effects of U-50, 488H after haloperidol pretreatment were identical to those previously demonstrated with the benzomorphan kappa agonist ethylketocyclazocine. Thus, haloperidol pretreatment unmasked the kappa opioid effects of U-50, 488H.

3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cycloh↗

PubMed2004

Human cortical EEG rhythms during long-term episodic memory task. A high-resolution EEG study of the HERA model.

Many recent neuroimaging studies of episodic memory have indicated an asymmetry in prefrontal involvement, with the left prefrontal cortex more involved than the right in encoding, the right more than the left in retrieval (hemispheric encoding and retrieval asymmetry, or HERA model). In this electroencephalographic (EEG) high-resolution study, we studied brain rhythmicity during a visual episodic memory (recognition) task. The theta (4-6 Hz), alpha (6-12 Hz) and gamma (28-48 Hz) oscillations were investigated during a visuospatial long-term episodic memory task including an encoding (ENC) and retrieval (RET) phases. During the ENC phase, 25 figures representing interiors of buildings ("indoor") were randomly intermingled with 25 figures representing landscapes ("landscapes"). Subject's response was given at left ("indoor") or right ("landscapes") mouse button. During the RET phase (1 h later), 25 figures representing previously presented "indoor" pictures ("tests") were randomly intermingled with 25 figures representing novel "indoor" ("distractors"). Again, a mouse response was required. Theta and alpha EEG results showed no change of frontal rhythmicity. In contrast, the HERA prediction of asymmetry was fitted only by EEG gamma responses, but only in the posterior parietal areas. The ENC phase was associated with gamma EEG oscillations over left parietal cortex. Afterward, the RET phase was associated with gamma EEG oscillations predominantly over right parietal cortex. The predicted HERA asymmetry was thus observed in an unexpected location. This discrepancy may be due to the differential sensitivity of neuroimaging methods to selected components of cognitive processing. The strict relation between gamma response and perception suggests that retrieval processes of long-term memory deeply impinged upon sensory representation of the stored material.

Adult↗

PubMed2003

Electroencephalographic(EEG)-based communication: EEG control versus system performance in humans.

People can learn to control electroencephalographic (EEG) sensorimotor rhythm amplitude so as to move a cursor to select among choices on a computer screen. We explored the dependence of system performance on EEG control. Users moved the cursor to reach a target at one of four possible locations. EEG control was measured as the correlation (r(2)) between rhythm amplitude and target location. Performance was measured as accuracy (% of targets hit) and as information transfer rate (bits/trial). The relationship between EEG control and accuracy can be approximated by a linear function that is constant for all users. The results facilitate offline predictions of the effects on performance of using different EEG features or combinations of features to control cursor movement.

Biofeedback, Psychology↗

PubMed1998

EEG power spectra of normal preadolescent twins. Gender differences of quantitative EEG maturation.

To determine developmental changes of quantitative EEG maturation, we investigated the electroencephalogram (EEG) power spectra in a sample of 72 pairs of healthy twins (144 subjects, 75 girls and 69 boys) ranging in age from 7-15 years. Main spectral parameters were measured in 16 EEG channels. The statistical significance of differences in the EEG power spectra was compared in relation to age and gender. Gender differences were tested by comparing the EEG parameters of boys and girls in the whole sample and separately in the subgroup of dizygotic twins of the opposite sex (DZO twin pairs). A statistically significant decrease of absolute power occurred with increasing age. A significant redistribution of relative power also appeared in higher age, mainly consisting of a progressive increase of alpha 2 power inversely related to relative alpha 1 and theta power. Polynomial regression models of the relation between alpha 2 and theta relative power with age were best described by a 5-order function. The mean frequency of activity across all spectra also increased with age and was maximal in the eldest subjects (13-15 years), with a significantly higher mean frequency of alpha 2 power in females. Similar age and gender differences were less marked in the subgroup of DZO twin pairs. The topographic distribution of spectral bands in normal subjects suggested an earlier maturation of midparietal or occipital than frontocentral regions, and indicated that the growth spurt does not occur simultaneously over homologous right and left hemisphere regions at the same age.

Adolescent↗

PubMed2003

Quality of EEG in simultaneous EEG-fMRI for epilepsy.

It is now possible to record the EEG continuously during fMRI studies. This is a very promising methodology that combines knowledge about neuronal activity and its metabolic response. The EEG recorded inside the fMRI scanner is, however,heavily contaminated by artifacts caused by the high intensity magnetic field and rapidly changing field gradients. Methods have been reported in the literature to reduce or eliminate these artifacts, in particular the ballistocardiogram and the artifact caused by currents induced by rapidly changing magnetic gradients. Nevertheless, recording the EEG simultaneously with fMRI remains an extremely delicate operation. In addition the use of artifact removal methods has only been reported by the laboratories in which they were developed. We report here the practical procedures we developed to reduce artifacts in a series of 10 epileptic patients, in the context of the visualization of epileptic spikes. We illustrate the effectiveness of methods designed to remove the scanning artifact and present new methods for removing the ballistocardiographic artifact. We present and evaluate techniques to obtain an EEG of good quality when performing simultaneous EEG and fMRI studies.

Artifacts↗