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Biomedical subjects

Z J Koles

Publications and source records attributed to Z J Koles.

15 recordsLinked to original sources
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↗
PubMed1979

Neuropsychological and power spectral EEG investigations of the obsessive-compulsive syndrome.

Eleven consecutive patients with primary obsessive-compulsive syndrome were studied neuropsychologically and the power spectral EEG characteristic of ten of these patients unmedicated, at rest, and during cognitive tasks were analyzed. The finding of predominantly left frontal dysfunction in the obsessional syndrome is discussed in the light of neurophysiological and psychosurgical evidence which suggest that perturbation of the cingulate-orbital frontal connections modulates obsessive-compulsive symptomatology.

Adult↗
PubMed1976

Mean velocity of optically detected intraaxonal particles measured by a cross-correlation method.

A method which uses by the cross correlation of optical signals is described for the determination of the mean velocity of somatopetally moving particles within nerve fibers. The method was validated by simulation experiments and by comparing the results with those obtained by averaging collections of velocities of individual particles. The significant contribution of the method is that it allows objective and rapid serial evaluation of mean particle velocity within individual nerve fibers with good accuracy and precision. A series of results from normal myelinated nerve fibers from Xenopus laevis is presented. Considerable variation (up to 50%) in mean velocity was found between individual nerve fibers. The mean of all determinations indicates that the mean velocity of somatopetally moving particles in axons with diameters greater than 10mum is in the region of 1.14 mum/s at a temperature of 22-24 degrees C. The findings are compared with small collection of such determinations which have been reported in the literature.

Animals↗
PubMed1972

A computer simulation of conduction in demyelinated nerve fibres.

1. The theoretical effects of demyelination on conduction of a propagated impulse have been examined in a computer simulated myelinated nerve fibre. Demyelination was simulated by increasing the capacitance and conductance of the myelin sheath of individual internodes or parts of internodes.2. Internodal conduction time increased as myelin thickness was decreased. The increase in internodal conduction time became more precipitous as the myelin became thinner. Propagation continued past a single demyelinated internode until myelin thickness was uniformly reduced to less than 2.7% of normal myelin thickness.3. Paranodal demyelination was more effective in slowing impulse conduction than was uniform demyelination of an entire internode with an equivalent rise in overall internodal capacitance and conductance.4. The effects on conduction of demyelination of two adjacent internodes or of two internodes separated by a normal internode were more than the sum of the effects of demyelination of each internode individually.5. Propagation across a severely demyelinated internode was blocked with an increase in internal sodium concentration which had a trivial effect on conduction in a normal fibre.6. Propagation across a severely demyelinated internode was blocked with increased temperature at a temperature at which propagation proceeds normally across normal internodes.7. The similarity between the findings of the computer simulations and the experimental findings in demyelinated fibres is discussed.

Action Potentials↗