Biomedical subjects

Z J Koles

Publications and source records attributed to Z J Koles.

At least 19 recordsLinked to original sources

PubMed1998

Trends in EEG source localization.

The concepts underlying the quantitative localization of the sources of the EEG inside the brain are reviewed along with the current and emerging approaches to the problem. The concepts mentioned include monopolar and dipolar source models and head models ranging from the spherical to the more realistic based on boundary and finite elements. The forward and inverse problems in electroencephalography are discussed, including the non-uniqueness of the inverse problem. The approaches to the solution of the inverse problem described include single and multiple time-slice localization, equivalent dipole localization and the weighted minimum norm. The multiple time-slice localization approach is highlighted as probably the best available at this time and is discussed in terms of the spatiotemporal model of the EEG. The effect of noise corruption, artifacts and the number of recording electrodes on the accuracy of source localization is also mentioned. It is suggested that the main appeal of the minimum norm is that it does not assume a model for the sources and provides an estimate of the current density everywhere in the three dimensional volume of the head.

Algorithms↗

PubMed1998

EEG source localization: implementing the spatio-temporal decomposition approach.

OBJECTIVES: The spatio-temporal decomposition (STD) approach was used to localize the sources of simulated electroencephalograms (EEGs) to gain experience with the approach for analyzing real data. METHODS: The STD approach used is similar to the multiple signal classification method (MUSIC) in that it requires the signal subspace containing the sources of interest to be isolated in the EEG measurement space. It is different from MUSIC in that it allows more general methods of spatio-temporal decomposition to be used that may be better suited to the background EEG. RESULTS: If the EEG data matrix is not corrupted by noise, the STD approach can be used to locate multiple dipole sources of the EEG one at a time without a priori knowledge of the number of active sources in the signal space. In addition, the common-spatial-patterns method of spatio-temporal decomposition is superior to the eigenvector decomposition for localizing activity that is ictal in nature. CONCLUSIONS: The STD approach appears to be able to provide a means of localizing the equivalent dipole sources of realistic brain sources and that, even under difficult noise conditions and only 2 or 3 s of available EEG, the precision of the localization can be as low as a few mm.

Artifacts↗

PubMed1997

Frequency domain discriminant analysis of the electroencephalogram.

A frequency domain generalization of the classical quadratic discriminant function was applied to the problem of classifying alpha-band multichannel electroencephalogram recordings in three task conditions. The data consisted of 41-channel recordings obtained in eyes closed, verbal, and spatial task conditions. Classifier performance was measured by deriving a decision rule from a training sample of 42 recordings and then applying the obtained rule to a test sample of 46 recordings. The proportion of correct classification was .93 in the training sample and .85 in the test sample. The classifier performed better when based on the complete cross-spectral matrix than when restricted to power spectrum variables. Classification based on a subset of 16 leads reduced the overall proportion of correct classification to .79 in the training sample and to .70 in the test sample.

Adolescent↗

PubMed1995

Spatio-temporal decomposition of the EEG: a general approach to the isolation and localization of sources.

The principal-component method of source localization for the background EEG is generalized to arbitrary spatio-temporal decompositions. It is shown that as long as the spatial patterns of the decomposition span the same signal space as the principal spatial components, the computational process of attempting to localize the sources is the same. Decompositions other than the principal components are shown to be superior for the EEG in that they appear to enable individual sources to be better isolated. An example is given using the common spatial pattern decomposition and using a raw varimax rotation of a subset of the common spatial patterns. The results show that the principal component decomposition is almost ineffective for isolating spike and sharp wave activity in an EEG from a patient with epilepsy, that the common spatial pattern decomposition is significantly better and that the varimax rotation is better yet. That the varimax rotation is best is demonstrated by attempting to locate dipole sources inside the brain which account for the spike and sharp wave activity on the scalp. The question which remains is whether there exists some oblique rotation of the basis vectors of the EEG signal space which is optimal for isolating individual sources.

Adult↗

PubMed1995

Principal-component localization of the sources of the background EEG.

A method, based on principal components for localizing the sources of the background EEG, is presented which overcomes the previous limitations of this approach. The spatiotemporal source model of the EEG is assumed to apply, and the method involves attempting to fit the spatial aspects of this general model with an optimal rotation of a subset of the principal components of a particular EEG. The method is shown to be equivalent to the subspace scanning method, a special case of the MUSIC algorithm, which enables multiple sources to be localized individually rather than all at once. The novel aspect of the new method is that it offers a way of selecting the relevant principal components for the localization problem. The relevant principal components are chosen by decomposing the EEG using spatial patterns common with a control EEG. These spatial patterns have the property that they account for maximally different proportions of the combined variances in the two EEG's. An example is given using a particular EEG from a neurologic patient. Components containing spike and sharp wave potentials are extracted, with respect to a standard EEG derived from 15 normal volunteers. Spike and sharp wave potentials are identified visually using the common spatial patterns decomposition and an EEG reconstructed from these components. Four dipole sources are fitted to the principal components of the reconstructed EEG and these source account for over 88% of the temporal variance present in that EEG.

Action Potentials↗

PubMed1994

Spatial patterns in the background EEG underlying mental disease in man.

The spatial patterns underlying differences in the background EEGs of schizophrenic, manic and depressed patients and a group of normal controls has been examined during the eyes open and eyes closed resting conditions and during 3 cognitive tasks. The method of principal-component analysis was used to extract spatial patterns which are common to the EEGs of 2 groups but which account for maximally different proportions of the combined variances. The common spatial patterns in all possible pairings of the groups were used to extract variance-related feature vectors from the individual EEG epochs in the 2 groups and the means of these vectors were subjected to statistical analyses. The results of these analyses indicate that there are significant differences in the EEGs from all 4 of the groups. The spatial patterns underlying the features which are significantly different in each comparison are shown graphically and used to suggest which brain regions might be implicated in each of the psychiatric conditions and how these are affected by the cognitive condition. The main results are that the EEGs in the schizophrenic group can be characterized by left-sided hyperactivity, in the depressed group by right-sided hyperactivity and in the manic group by bilateral hyperactivity and that these characteristics are best elicited by different cognitive states.

Adult↗

PubMed1993

Systematic comparisons of interpolation techniques in topographic brain mapping.

The performance of one local interpolation technique, the nearest neighbors, and two global spline techniques, one planar and the other spherical, commonly used for topographic mapping of brain potential data has been quantitatively evaluated. The method of evaluation was one of cross-validation where the potential at each site in a 31-electrode full scalp recording montage is predicted by interpolation from the other sites. Errors between the measured potentials and those predicted by interpolation were quantified using 4 measures defined as inaccuracy, precision, bias and tolerance. The evaluation was applied to the background EEGs from 5 normal volunteers and from 4 patients with epilepsy, tumor or stroke. The results indicate that none of the interpolation techniques performed well and that for localized components in the EEG, the errors can increase almost without limit. Further, the global techniques performed significantly better than the local technique with 2 being the best order for the nearest-neighbor technique and 3 for the spline techniques. It is concluded that interpolation should not be used with electrode densities of the order of that provided by the international 10-20 system neither to increase the spatial resolution of the electroencephalogram nor in more sophisticated analysis techniques in quantitative EEG for estimates such as the radial-current density.

Brain↗

PubMed1991

The quantitative extraction and topographic mapping of the abnormal components in the clinical EEG.

A method is described which seems to be effective for extracting the abnormal components from the clinical EEG. The approach involves the use of a set a spatial patterns which are common to recorded and 'normal' EEGs and which can account for maximally different proportions of the combined variances in both EEGs. These spatial factors are used to decompose the EEG into orthogonal temporal wave forms which can be judged by the expert electroencephalographer to be abnormal, normal or of artifactual origin. The original EEG is then reconstructed using only the abnormal components and principal component analysis is used to present the spatial topography of the abnormal components. The effectiveness of the method is discussed along with its value for localization of abnormal sources. It is suggested, in conclusion, that the approach described may be optimal for interpretation of the clinical EEG since it allows what is best in terms of quantitative analysis of the EEG to be combined with the best that is available in terms of expert qualitative analysis.

Brain↗

PubMed1991

Quantitative EEG studies of pedophilia.

Ninety six pedophiles, whose sexual orientation was confirmed by phallometric response to sexual stimuli, were investigated with quantitative EEG and compared to age- and sex-matched healthy controls. The EEG analysis showed a pattern of increased frontal delta, theta and alpha power (especially during verbal processing) and a pattern of reduced interhemispheric and increased intrahemispheric-interhemispheric coherence, right and left (only during verbal processing), an effect that was restricted to those who showed maximal erotic arousal for sexual partners aged 6-12 years. These findings will be discussed in the context of recent studies which suggest that sexual deviations in the male relate to altered dominant hemispheric functions with disruption of frontal interhemispheric relationships.

Brain↗

PubMed1990

Spatial patterns underlying population differences in the background EEG.

A method is described which can be used to extract common spatial patterns underlying the EEGs from two human populations. These spatial patterns account, in the least-squares sense, maximally for the variance in the EEGs from one population and minimally for the variance in the other population and therefore would seem to be optimal for quantitatively discriminating between the individual EEGs in the two populations. By using this method, it is suggested that the problems associated with the more common approach to discriminating EEGs, significance probability mapping, can be avoided. The method is tested using EEGs from a population of normal subjects and using the EEGs from a population of patients with neurologic disorders. The results in most cases are excellent and the misclassification which occurs in some cases is attributed to the nonhomogeneity of the patient population particularly. The advantages of the method for feature selection, for automatically classifying the clinical EEG, and with respect to the reference-free nature of the selected features are discussed.

Adolescent↗

PubMed1990

A spatial power spectrum analysis of the electroencephalogram.

The method of spatial power-spectrum analysis has been applied to measurements of the distribution of rms alpha-band potential on the scalp. Data was recorded using the 31-Electrode System and spatial power-spectrum estimates (PSEs) were obtained from Mercator projections of the potential interpolated using the triangular method. PSEs were calculated using the Lim and Malik algorithm for maximum-entropy power-spectrum estimation. In order to investigate the utility of spatial power-spectrum analysis, PSEs were obtained from subjects in two conditions; resting with eyes closed (EC) and resting with eyes open and fixed on a single point (EO). A stepwise discriminant analysis was performed with features from the PSEs and the resultant discriminant function was applied to data not considered in the formulation of the function. Over 92% of test data was correctly classified. The features used in the discriminant function identify spatial waves which are most useful in separating data. The results demonstrate that waves oriented along front-back and right-left lines are most important in separating data into EC and EO groups.

Brain↗

PubMed1990

Neurophysiological and neuropsychological study of two cases of multiple personality syndrome and comparison with chronic hysteria.

Two cases of multiple personality were studied neurophysiologically and neuropsychologically. Bilateral frontal (Right greater than Left) and left temporal dysfunction was present in both cases, on neuropsychological indicators. Both cases on EEG analysis, were in a state of relative left hemisphere activation, across all cerebral regions and task conditions. The one case who was cured with hypnotherapy, after recovery showed normal left hemisphere functions neuropsychologically but remained in a state of relative left hemisphere activation electrophysiologically. This is in contrast to women with chronic hysteria who exhibit relative right hemisphere activation in all regions and across all conditions. Both patients were unmedicated throughout. A neurophysiological model to account for these findings is presented.

Adult↗

PubMed1989

Computed radial-current topography of the brain: patterns associated with the normal and abnormal EEG.

We describe a method for producing estimates of radial-current topography underlying the background EEG. This method is based on the application of the laplacian operator to potentials measured on the scalp using a 31-electrode recording array. The laplacian is applied analytically to a potential surface obtained by bicubic-spline interpolation of the measurements at the electrode sites. The results obtained when the method was applied to the alpha rhythm recorded from a normal volunteer and to the slow wave activity recorded from a neurologic patient are presented. The alpha rhythm is associated with areas of strong radial-current activity in the occipital regions (although dominantly right); for the slow rhythm the activity appears in the medial-frontal region. The radial-current topography for the alpha rhythm suggests rotating dipole generators in the occipital lobes whereas it is suggestive of a radially oriented dipole in the case of the delta activity. Discussion is focused upon the apparent advantages of radial-current topography for localizing brain electrical activity, upon the strengths and weaknesses of the method, and upon the observation that the topography of radial current activity obtained would have been difficult to predict from a visual examination of raw EEG traces alone.

Adult↗

PubMed1988

Topographic mapping of the EEG: an examination of accuracy and precision.

The accuracy and precision of topographic maps depicting scalp potentials and scalp potentials squared have been examined. Electrode placement was that specified by the International 10-20 System and the methods of interpolation bilinear and bicubic spines. The results indicate that, for these interpolation methods, the maximum error expected between the measured scalp quantities and those predicted by interpolation is positively correlated to the root-mean-square value of the measured quantity. Both interpolation methods produce accurate estimates of the interelectrode quantities. Both methods produce precise estimates of the scalp potential in the delta, theta and alpha frequency bands but only poor estimates in the beta band. The precision of the estimates of the scalp potentials squared is poor in all frequency bands. This result indicates that another look at the now common practice of topographically mapping the power-spectral components of the EEG is in order. In general, the bilinear and bicubic spline methods of interpolation perform about equally. This result is used to suggest that because of its additional computational complexity, use of the bicubic method for potential mapping may not be warranted. Advantages of the bicubic method, particularly in radial-current mapping, are however discussed.

Adult↗

PubMed1987

The effect of brain function on coherence patterns in the bipolar EEG.

Studies of the functional organization of the brain based on measurements of coherence in the EEG have, in the past, suffered from a methodological defect which has made interpretation of the results difficult. The effect involved is the use of an active common reference for the recording of the EEG. As a consequence, inferences related to the functional connectivity of brain between the non-referential sites using coherence have probably been wrong. To avoid the problem with the common reference, we have used bipolar derivations of the EEG and used measurements of coherence to reflect synchrony not between individual sites but between regions of the brain. The EEGs in a population of normal volunteers were examined with respect to coherence. Changes in the patterning of coherence were induced by utilizing EEGs from the volunteers during 3 different functional brain states. The first of these was the resting state, the second the verbal motor state and the third, the spatial motor state. The stepwise discriminant analysis method was used to study differences in the patterning of coherences in the 3 states. The results show that the spatial motor state was the most distinct in this regard amongst the 3 states. They results also interpreted as indicating that changes in the patterning of coherence from that in the resting state consisted of both functionally specific and functionally non-specific components.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗

PubMed1987

The effects of dialysis on brain water and EEG in stable chronic uremia.

Cerebral edema in uremic animals and humans, as well as an EEG deterioration in humans, has been reported after dialysis. Both are manifestations of the dialysis disequilibrium syndrome (DDS). This study was designed to analyze the changes induced by dialysis in the EEG pattern (spectral analysis), in the cerebral hydration, and ventricular size (computed tomography [CT] of the brain) in a group of 11 stable uremic patients. They volunteered for a randomized crossover study of 4 months each of standard hemodialysis (HD) and hypertonic hemodiafiltration (H HDF). H HDF is a dialysis technique that is shorter and more efficient than HD. An EEG recording, a CT scan of the brain, and blood biochemistry were performed before and after a HD (four hours, blood flow rate 250 mL/min) and a H HDF run (three hours, blood flow rate 400 mL/min). Approximately 6 weeks of stabilization on each treatment were allowed before these studies. No difference was found in the density of seven specific brain structures (base and apical cuts), when comparing pre- v post-HD, pre- v post-H HDF, pre- HD v pre-H HDF, and post-HD v post-H HDF. Furthermore, no difference was evident either in the bicaudate diameter of the lateral ventricles or in the transverse diameter of the third ventricle. In addition, no significant in-between- and within-treatment difference was observed when analyzing the EEG% power (3-7/7-13 Hz) data. In conclusion, this study shows neither a postdialysis change in brain density and ventricular size nor a postdialysis EEG deterioration in a group of stable uremic patients undergoing both a rapid and a standard dialysis treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1984

Statistical quantitative EEG studies of depression, mania, schizophrenia and normals.

The EEG characteristics of 63 depressive psychotics, 75 manics and 53 schizophrenic patients, consecutive admissions satisfying research criteria, are presented. Statistical comparisons between the psychotic groups and of each psychotic group against 60 normal controls (all dextral) were undertaken for power, coherence and phase characteristics in the 8-13 Hz frequency band. The characteristic EEG-myogenic power spectra for frequencies up to 60 Hz, expressed as the log of the right/left parietal and temporal power ratios for the four groups are also graphically displayed. The results suggest the presence of increasing disorganization of the right hemisphere (least in depression, intermediate in mania and maximal in schizophrenia) together with left hemisphere disorganization (in both mania and schizophrenia; again maximal in schizophrenia).

Adolescent↗

PubMed1983

Oscillatory motion of intra-axonal organelles of Xenopus laevis following inhibition of their rapid transport.

The motion of optically detected organelles in myelinated axons of Xenopus laevis was studied in axons bathed in a potassium glutamate based medium and in axons in a similar medium to which various inhibitors of axonal transport were added. Organelles in the potassium glutamate medium had a motion which was indistinguishable from that previously described for organelles in axons bathed in a conventional physiological saline. Colchicine, dimethylsulphoxide, 2,4-dinitrophenol, hyperosmotic solutions, raised concentrations of intracellular calcium ions, and media made up in deuterium oxide caused either a complete or partial inhibition of both anterograde and retrograde organelle transport. When directioned transport had been inhibited by any of the agents used, organelles displayed a longitudinally oriented oscillatory motion. An analysis of the variable, or oscillatory, component of organelle motion in axons not treated with inhibitors and in axons in which transport was partially or completely inhibited produced evidence that the dominant frequency components were similar in each case. A maximal estimate of the dominant frequency of oscillatory motion was 0.18 +/- 0.02 Hz. The distribution of instantaneous velocities about the mean velocity was not substantially altered as the transport of organelles was inhibited. The evidence suggested that the variable component of motion of organelles which show directioned transport is related to the oscillatory motion of organelles whose transport is inhibited.

2,4-Dinitrophenol↗