EEG Analysis Methods Research Articles

A shift in information flow between prefrontal cortex and the ventral tegmental area in methamphetamine-sensitized rats

We examined the effects of long-term methamphetamine (MAP) administration to rats on locomotor traces and reward-seeking behavior that was evaluated through ventral tegmental intracranial self-stimulation (ICSS). Furthermore, using the directed coherence (DCOH) EEG analysis method, correlation of prefrontal cortical and ventral tegmental EEGs was investigated in terms of the direction of information transmission. The results showed a transition from ‘mixed type’ behavior to ‘fixed type’ behavior during long-term MAP treatment, accompanied by a gradually diminished rate of ICSS and increased reward threshold. Correlating to these changes, a dominant information flow from ventral tegmental area (VTA) to prefrontal cortex (PFC) was observed after long-term MAP administration. Together with our previously reported finding of reciprocal information flow between PFC and VTA in MAP-induced hyperactive and stereotyped behavior, the present results indicate that information flow and its direction may be useful in explaining the neuronal substrates mediating development of behavioral sensitization. The predominant information flow from the VTA to PFC that occurs with sensitization supports recent speculations concerning impulsivity in drug addiction.

Electroencephalogram analysis using fast wavelet transform

The continuous wavelet transform is a new approach to the problem of time–frequency analysis of signals such as electroencephalogram (EEG) and is a promising method for EEG analysis. However, it requires a convolution integral in the time domain, so the amount of computation is enormous. In this paper, we propose a fast wavelet transform (FWT) that the corrected basic fast algorithm (CBFA) and the fast wavelet transform for high accuracy (FWTH). As a result, our fast wavelet transform can achieve high computation speed and at the same time to improve the computational accuracy. The CBFA uses the mother wavelets whose frequencies are 2 octaves lower than the Nyquist frequency in the basic fast algorithm. The FWT for high accuracy is realized by using upsampling based on a L-Spline interpolation. The experimental results demonstrate advantages of our approach and show its effectiveness for EEG analysis.

Unbiased high resolution method of EEG analysis in time-frequency space

Matching Pursuit (MP) - a method of high-resolution signal analysis - is described in the context of other methods operating in time-frequency space. The method relies on an adaptive approximation of a signal by means of waveforms chosen from a very large and redundant dictionary of functions. The MP performance is illustrated by simulations and examples of sleep spindles and slow wave activity analysis. An improvement of the original procedure, relying on the introduction of stochastic dictionaries, is proposed. A comparison of the performance of dyadic and stochastic dictionaries is presented. MP with stochastic dictionaries is characterized by an unmatched resolution in time-frequency space; moreover it allows for parametric description of all (periodic and transient) signal features in the framework of the same formalism. Matching pursuit is especially suitable for analysis of non-stationary signals and is a unique tool for the investigation of dynamic changes of brain activity.

Topographic Time-Frequency Decomposition of the EEG

Frequency-transformed EEG resting data has been widely used to describe normal and abnormal brain functional states as function of the spectral power in different frequency bands. This has yielded a series of clinically relevant findings. However, by transforming the EEG into the frequency domain, the initially excellent time resolution of time-domain EEG is lost. The topographic time-frequency decomposition is a novel computerized EEG analysis method that combines previously available techniques from time-domain spatial EEG analysis and time-frequency decomposition of single-channel time series. It yields a new, physiologically and statistically plausible topographic time-frequency representation of human multichannel EEG. The original EEG is accounted by the coefficients of a large set of user defined EEG like time-series, which are optimized for maximal spatial smoothness and minimal norm. These coefficients are then reduced to a small number of model scalp field configurations, which vary in intensity as a function of time and frequency. The result is thus a small number of EEG field configurations, each with a corresponding time-frequency (Wigner) plot. The method has several advantages: It does not assume that the data is composed of orthogonal elements, it does not assume stationarity, it produces topographical maps and it allows to include user-defined, specific EEG elements, such as spike and wave patterns. After a formal introduction of the method, several examples are given, which include artificial data and multichannel EEG during different physiological and pathological conditions.

Monitorage de lˈélectroencéphalogramme : techniques, indications, intérêt en réanimation

Continuous electroencephalography (EEG) monitoring has only recently begun to be developed in intensive care units. Digital EEG technology and the development of new methods of automatic EEG analysis have allowed this method to become a clinically relevant tool. Analysis of the continuous EEG requires a perfect knowledge of recording conditions, which must be as rigorous as possible. The interpretation made by an expert must remain cautious. The primary current indication of continuous EEG monitoring in intensive care units is status epilepticus. EEG monitoring is very useful to all the phases of the management of status epilepticus when the clinical neurological situation does not improve rapidly. The duration of the monitoring can go from 24 hours to several weeks. It can be useful for the diagnosis of nonconvulsive seizures; it allows a better management of anaesthetic drugs during refractory status epilepticus; and it allows the detection of recurrent seizures after tapering of the treatment. New indications start to emerge: monitoring of severe acute head trauma, early detection of focal cerebral ischemia and monitoring of coma. This technique, which improves the management of neurological patients, promises to develop further in the future.

Agents pharmacologiques épileptogènes en anesthésie

Most anaesthetics and analgesics have both pro- and anticonvulsant activity. The data in the literature should be analysed with respect to the patient population, the recording of epileptic activity and the method of EEG analysis. Among inhaled anaesthetics, isoflurane has strong anticonvulsant properties. In some circumstances, sevoflurane may induce an epileptic activity. With the exception of ketamine and etomidate, all intravenous hypnotics may be used for anesthesia of the epileptic patient. Midazolam is a potent anticonvulsant. Among narcotics, fentanyl and alfentanil may induce clinical or electroencephalographic seizures. Considering the large number of patients treated with these agents without any neurological adverse effect, the clinical relevance of these data is unclear. Neuromuscular blocking agents do not possess pro- or anticonvulsant properties.

Prospects for routine detection of dementia using the fractal dimension of the human electroencephalogram

The paper datails research which aims to improve the contribution made by electroencephalogram (EEG) analysis to the diagnosis and care of patients with brain disease; dementia in particular. Previous attempts to automate EEG analysis have concentrated on separating patient groups from control groups, often on the basis of a single neurophysiological index derived from a short, isolated segment of EEG. The authors seek to develop, and test, a novel technique for the analysis of changes in serial EEG recordings on individuals (subject-specific analysis) which may serve as a basis for routine early detection of dementia. The objectives of the reported study were to examine the feasibility of applying appropriate fractal dimension (FD) (complexity) measures to the human EEG, and to examine whether methods using the subject specific variability of these measures are likely to be useful for detecting patients who develop dementia. The reason for undertaking the study was to establish a ‘proof of concept’ and determine whether research should concentrate in this area. Existing EEG analysis methods were reviewed and four FD measures suitable for EEG analysis were developed. These four measures were applied to a total of 21 EEG recordings (from seven subjects with various dementias, eight age matched controls and two young subjects who gave three recordings each). The results were analysed and the following conclusions were drawn: it is possible to measure the complexity of the human EEG using the FD, and the subject specific variability of the FD is an important candidate method for identifying patients with dementia. Therefore, further work in this area is justified.

Nonlinearity in human resting, eyes-closed EEG: an in-depth case study

The question of nonlinearity in the human electroencephalogram (EEG) is important, since linear methods of EEG analysis are more well-developed and computationally faster than nonlinear methods. Furthermore, the presence or absence of nonlinearity has important theoretical implications for understanding the nature of the brain's oscillatory activity. Using a linear summary measure as a control, we report a failure to reject the null hypothesis of a (largely) stationary linear-Gaussian process for normal, resting, eyes-closed EEG from a single participant. We found significant evidence of nonlinearity at two occipital sites (01 and 02) where the 8-12.5 Hz alpha rhythm was prominent. However, this element of nonlinear structure appeared trivial, as (1) we found no evidence of time irreversibility at these loci, and (2) best-fitting linear models accounted on-average for over 94% of the variance in the data with nonlinear modeling doing no better. Half of the remaining variance could be accounted for by nonstationarity. While our findings technically apply only to the one individual tested, his EEG was typical of those seen under the conditions that we employed.

Injury Detection for Central Nervous System via EEG with Higher Order Crossing-based Methods

Higher order crossing (HOC) is a powerful tool for time series analysis. Two HOC-based EEG analysis methods are developed for brain injury detection and quantification. The first method explores EEG spectrum characteristics via an estimate of the dominant frequency of a pre-processed EEG signal. The second method is based on the norm of the AHOC, an HOC obtained from the alpha-filter prefiltered EEG signal. Both methods are shown to be effective in detecting hypoxic/asphyxic injuries as well as assessing the severity of the injury.

Dream content of patients with sleep apnea

Previous research has shown that external stimuli were often incorporated into the dream to some extend. The aim of the present study was to investigate whether the internal stimulus sleep apnea is also incorporated into dreams. Findings showed, however, that direct incorporation occurs very seldom. On the other hand, arousals accompanying sleep apneas seem to interfere with dream formation since a marked reduction of dream bizarreness is related to high RDI (respiratory disturbance index). Additionally, small indirect effects on dream content by day-time stressors such as cognitive deficits and sleepiness are suggested by the data. A heightened dream recall frequency in patients with sleep apnea was found. Future dream research should focus on studies including sophisticated EEG analysis methods and detailed measures of day-time symptoms present in patients with sleep apnea.

High temporal resolution dynamic mapping of instantaneous EEG amplitude modulation after tone-burst auditory stimulation.

A new method of instantaneous EEG analysis based on amplitude modulation (AM-EEG) was applied to analyze the AM-EEG changes in the alpha frequency band (8.20-12.89 Hz) for successive 5 ms epochs. Repeated auditory tone-burst stimuli (of 220 ms duration) were presented at fixed 2.56 second intervals to 12 attending right-handed young female volunteers, who were EEG-recorded over 19 EEG channels at 200 Hz sampling frequency. The time-course of functional activation was characterized in terms of percent decrease in instantaneous amplitude modulation, as compared to baseline, in analogy with the classical event-related desynchronization paradigm. A dynamic sequence of the successive 122 AM-EEG maps obtained for the 610 ms from beginning of tone-burst was stored and later animated on PC microcomputer. Topological changes among successive maps were extracted into 40 specific AM-EEG maps. Early left temporal and centro-temporal activation was observed, followed first by strong bilateral frontal, and then by left temporal activation. These changes induced by a warning tone-burst are discussed in terms of functional neurophysiology. The present method therefore allows an improved time-resolution for functional brain activation paradigms.

Automatic EEG analysis during long-term monitoring in the ICU

To assist in the reviewing of prolonged EEGs, we have developed an automatic EEG analysis method that can be used to compress the prolonged EEG into two pages. The proposed approach of Automatic Analysis of Segmented-EEG (AAS-EEG) consists of 4 basic steps: (1) segmentation; (2) feature extraction; (3) classification; and (4) presentation. The idea is to break down the EEG into stationary segments and extract features that can be used to classify the segments into groups of like patterns. The final step involves the presentation of the processed data in a compressed form. This is done by providing the EEGer with a representative sample from each group of EEG patterns and a compressed time profile of the complete EEG. To verify the above approach, 41 6 h EEG records were assessed for normality via the AAS-EEG and conventional EEG approaches. The difference between the overall assessment via compressed and conventional EEG was within one abnormality level 100% of the time, and within one-half level for 73.6% of the records. We demonstrated the feasibility and reliability of automatically segmenting and clustering the EEG, thus allowing the reduction of a 6 h tracing to a few representative segments and their time sequence. This should facilitate review of long recordings during monitoring in the ICU.

Neural networks as a new method for EEG analysis. A basic introduction.

This paper discusses the general usability of artificial neural networks for the analysis of EEG data. The advantages and drawbacks of this new technology are compared, especially from the perspective of medical computer science. Furthermore this text clarifies the fundamental principles of neural networks, the relations to the biological model and how they compare to classical evaluation methods.

Hypnotics and sleep physiology: A consensus repot

The effects of hypnotics on descriptive and functional aspects of electrophysiological sleep parameters are assessed in this report. Because of the arbitrary definition of some of the criteria underlying the conventional sleep stage scoring procedure, computer-aided methods of EEG analysis have become increasingly important for recording and interpreting pharmacological effects on sleep. Of particular interest are the changes of EEG slow-wave activity, since this parameter varies as a function of prior sleep and waking. Several types of interaction between hypnotics and sleep regulation are discussed, some recent pharmacological developments are highlighted, and some common problems in clinical trials are specified.

Pro- and Anticonvulsant Effects of Anesthetics (Part II)

Perioperative seizures have numerous potential etiologies. In general, when seizures occur during surgery, their onset often coincides with the introduction of a specific anesthetic or analgesic drug. Conversely, postoperative seizures are more commonly due to nonanesthetic causes. However, there have been reports of postoperative convulsions that appeared to be caused by anesthetic or analgesic drugs administered intraoperatively via inhalation or injection (e.g., intravenous, epidural, or peripheral nerve block). Some anesthetics appear to possess both proconvulsant and anticonvulsant properties. One possible factor is an inherent pharmacodynamic variability in the responsiveness of inhibitory and excitatory target tissues in the CNS. This is well illustrated by the anticonvulsant and proconvulsant effects of progressively higher doses of local anesthetic drugs. This variability in neuronal responsiveness could also explain the conflicting findings for low versus high doses of fentanyl and etomidate. Furthermore, biological variation in the individual patient's responsiveness to certain anesthetic drugs could be an additional contributory factor. Differing structure-activity relationships might also explain why some anesthetic agents possess both proconvulsant and anticonvulsant properties. Relatively minor modifications in a drug's structure can influence its affinity for a specific receptor site and its intrinsic pharmacologic activity. For example, when methohexital was first introduced, convulsions were commonly encountered in patients with and without a history of epilepsy. Subsequent fractionation of the original compound into its two isomeric forms resulted in the identification of the isomer primarily responsible for this convulsive activity. In its present formulation (Brevital; Eli Lilly, Indianapolis, Ind.), the epileptogenic properties of methohexital are limited to patients with psychomotor epilepsy. However, compared with thiopental, excitatory effects are still more common with methohexital. The excitatory effects of methohexital are presumably due to its methylated structure. The inhaled anesthetic flurothyl (hexaflurodiethyl) ether and the intravenous anesthetic ketamine also illustrate how subtle changes in stereoisomerism can result in significant changes in structure-activity relationships. Flurothyl, a fluorinated ether analogue, reliably produces convulsions in nonepileptic patients, whereas its structural isomer isoindoklon has not been associated with seizure activity. Other examples of isomer or structural analogue relationships that produce differential effects on neuronal hyperexcitability include enflurane-isoflurane and meperidine-normeperidine. In conclusion, the patient population (epileptic or nonepileptic), the method of documentation (EEG study or clinical observation), and the method of EEG analysis (cortical or depth electrodes) must be considered to properly analyze the proconvulsant and/or anticonvulsant properties of an anesthetic or analgesic drug.(ABSTRACT TRUNCATED AT 400 WORDS)

EEG and Lithium CNS Toxicity

ABSTRACT.Lithium is a unique mood stabilizing agent with antimanic, antidepressant, and prophylactic properties for the management of recurrent affective illnesses. Lithium produces diffuse EEG slowing and paroxysmal activity which is more pronounced during chronic treatment than after a single acute dose and still more prominent during intoxication. EEG effects of lithium have been studied in patients with affective disorders and in normals as well as in adults and children with mainly consistent findings. The EEG is a more reliable indicator of neurotoxicity with lithium than are measures of plasma levels. Nevertheless there can be difficulty in discriminating between EEG alterations associated with therapeutic levels as opposed to toxicity. Quantitative methods of EEG analysis may offer more sensitive means of discrimination. There is an increased risk of lithium intoxication in patients with certain psychiatric diagnoses as well as in the elderly and in patients with underlying medical disorders. Toxi...

A microprocessor device for the real-time detection of synchronized alpha and spindle activity in the EEG

A microprocessor based device is described which permits the real-time detection of synchronized EEG activity within the frequency range of the alpha rhythm or sleep spindles. This device offers a reliable, inexpensive method for EEG analysis according to flexible, user selectable parameters. It can be used either on-line or off-line and provides information as to the occurrence and duration of alpha-spindle EEG activity.

The use of the time domain analyzed EEG in conjunction with cardiovascular parameters for monitoring anesthetic levels.

A simple time domain method of EEG analysis based upon the computation of the frequency and the amplitude of the zeroth, first, and second derivative of the EEG wave has been developed for monitoring the anesthetic level of patients undergoing general anesthesia. This study explores the effectiveness of this EEG analytical system working in conjunction with cardiovascular parameters in discriminating among commonly used anesthetic dosages. EEG features and cardiovascular features were used as variables in a stepwise discriminant analysis on two patient group sets each using a light, medium, and deep dosage level of the agents halothane/nitrous oxide and enflurane/nitrous oxide, respectively. The best overall discriminant prediction of the three 30-patient groups using halothane and nitrous oxide was 86.7 percent correct. The best overall discriminant prediction of the three 30-patient groups using enflurane and nitrous oxide was 90 percent correct. It was felt that these accuracies were sufficient to continue development of this sytem, the next step being the determination of a suitable anesthetic depth scale based upon the use of these and perhaps additional physiological features.

Some Programs for the Processing of Eeg Data on a Small General Purpose Digital Computer

The paper describes and illustrates some techniques for the processing of EEG data using a small digital computer VARIAN'73. The normal EEG background activity were studied for amplitude analysis, interval analysis, correlation analysis, pattern recognition, frequency analysis, Hjorth parameters (activity, mobility, complexity). Such combined methods of automatic EEG analysis were used in 30 patients with "petit-mal" from whom serial EEGs were obtained. Some significant results are presented. All thease methods provide precise statistical and mathematical descriptors of an episode in time, giving a better quantitative evaluation of the global EEG picture.

Functional Interhemispheric Differences in Relation to Various Psychopathological Components of the Depressive Syndromes

Previous investigations from our laboratory have suggested a possible interhemispheric difference in brain functioning in relation to the severity of a depressive psychopathological process. The present study has been carried out to extend the previous findings to comprise a more detailed symptom analysis of the depressive syndrome, several EEG characteristics, and a new method of EEG analysis. 22 depressed patients, most of them previously untreated, participated in the study. The patients were rated by means of a highly reliable rating scale for depression, and an EEG record was obtained from each of them. Analysis of possible relationships among clinical symptoms and EEG characteristics from different parts of the brain showed a complex pattern, quite different for each symptom. First when a systemic structural analysis of the EEG was performed by means of a special computer program, differential EEG syndromes could be identified. Patients with a high level of anxiety-depression showed a more pronounced functional involvement of the left precentral region than less severely ill patients.