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Biomedical subjects

Iu M Koptelov

Publications and source records attributed to Iu M Koptelov.

At least 19 recordsLinked to original sources
PubMed2001

[Change of bioelectric brain activity registered at the distance from the focus of cerebral tissue injury].

The focal delta-waves and the remote influences of the stroke in the form of the sinusoidal flashes of delta-waves with a maximal amplitude exceeding an amplitude of the focal delta-waves (frontal flashes--FF) in frontal-polar leads were investigated in 51 patients (22 men, 29 women) by means of mapping, dipole location (BrainLoc) and LORETA methods. The patients were examined in dynamics during the acute period of hemispheric stroke on days 1-3, 14 and 21 after the onset of the disease. The usage of the modern computer methods of EEG analysis permits to consider FF as an independent electrophysiological phenomenon and to localize a zone of the sources of such flashes, which does not coincide with the zone of generation of the focal delta-activity that corresponds to the perifocal zone of the stroke. According to the data of the three-dimensional location a probable zone of FF generation corresponds to the frontal pole and medial-basal areas of the frontal lobe. Comparison with the MRI data leads to the conclusion that a damage of anterior white substance was the most frequent cause of FF development, probably by deafferentation mechanism. FF may be an electrophysiological manifestation of the influence of the damage of the different brain structures on the frontal lobes according to diaschisis mechanism.

Acute Disease↗
PubMed1992

[Interhemispheric correlations of electric activity of the brain in late depression].

A chronometric EEG analysis was made in 60 patients aged 50 to 86 years with affective psychosis in different stages of the depressive phase. It has been demonstrated that the development of depressive conditions gives rise not only to changes in the frequency and amplitude characteristics of the EEG but also in the ratios of interhemispheric asymmetry of the parameters of brain electric activity, attesting to a higher tone of the right hemisphere. This interhemispheric asymmetry was determined to a considerable measure by the presence in the reference EEG of generalized discharges of slow-wave activity. The use of the dipolar analysis of the EEG permitted detecting foci of maximum generation of discharges in the left temporal area and brain stem structures. These areas of generation were preserved after removing the depressive symptomatology with antidepressants. It is suggested that the superstem generators of discharges exert a more appreciable effect on right hemisphere function, which is specified by cortico-diencephalic relations.

Age Factors↗
PubMed1989

[Analysis of "scalp potential fields" and the tridimensional location of the sources of epileptic activation in humans].

The method of multi-step dipole localization with potential charts preanalysis was applied to EEG spatial localization of discharge activity in 24 epileptic patients. The results were juxtaposed to the X-ray contrasting techniques and computerized tomography. Spherical symmetrical 8-layer head model was used to interprete the results. The data on three-dimensional localization of focal and generalized paroxysmal activities are presented. The role of this technique in differentiating the primarily generalized activity from secondary foci is outlined. The generation and recording sites epileptic activity could diverge largely due to the primary source orientation. For correct EEG interpretation, it is important that the primary generation zone be reconstructed. This is an additional field of application of this technique.

Action Potentials↗
PubMed1981

[Possibility of 3-dimensional localization of EEG sources based on an equivalent dipole model].

Coordinates and moments of equivalent sources of certain kinds of EEG normal and pathological activity--alpha-rhythm, focal and generalized epiactivity--were estimated on a computer on the basis of a homogeneous model of a single equivalent dipole, by a modified method of the direct search. Cartesian coordinates of electrodes located according to the standard scheme 10--20 were preliminarily estimated. Precision of recovering source coordinates was determined on an agar two-layer spherical model with different localization of the stimulating electrode inside the sphere. The estimated coordinates of normal activity sources are compared with the data of electrophysiological studies of the waves genesis, and those for pathological activity, with real coordinates of the pathological focus.

Alpha Rhythm↗
PubMed1979

[Spectral and integral-temporal analysis of cerebral evoked potentials in epilepsy patients].

Changes in the spectral and integral-temporal characteristics of evoked potentials (EP) to flashes, were studied in 17 epileptic patients and 20 normals. The analysis of EP was done on a background recording and after a 2-minute hyperventilation. It was demonstrated that an epileptization of the brain according to the integral indices of EP is expressed by an increase in the square response, duration of EP (an increase in the duration of the system return to a state of equilibrium), by a higher level of residual noise in a discharge of EP, as well as by an increase in the negative part of EP and a larger instability of responses. The spectral content of EP in epileptic patients demonstrates an increase in amplitude maxima, especially within theta = psi delta ranges. Hyperventilation in epileptic patients evokes a pronounced synchronization of brain bioelectric activity, which leads to a drop of the response intensity and an increase in the level of residual noise in a discharge of EP. The data obtained suggest that the proposed method of EP analysis may be effective in the determination of the intensity in the focus of epileptical activity, as well as in the study of the function of inhibitory mechanisms of convulsive discharges.

Electroencephalography↗
PubMedDate not supplied

[Generators of the rhythmic alpha activity in the human EEG].

An attempt to localize brain mechanisms of the rhythmic activity in the alpha-rhythm range was made using the equivalent dipole model. It is known that light flickering stimuli with the frequency close to that of the individual alpha rhythm induce an increase in its spectral power ("photic-driving" phenomenon). It was shown that the activity of the neuronal structures generating the alpha rhythm can be identified by specific frequency of the light stimulation and localized by means of construction of dipole models. Two sources of the alpha rhythm in the narrow-frequency bands with the maximal resonance responses in the frequencies of 10.1 and 10.5 Hz were localized in the thalamic structures.

Alpha Rhythm↗
PubMedDate not supplied

[Characteristics of the spatio-temporal organization of the P300 component of AEP during the "active" and "passive" stimulus perception in healthy subjects].

The concern of the work was in detection and analysis of P300 component of the acoustic evoked potential in healthy subjects in different experimental situations. During counting the rare sounds, P300 was most pronounced in the frontocentral and parietooccipital areas mainly of the left-hemisphere. The response shape was correlated with characteristics of the basic rhythm of the background EEG. Responses of simple and complex shapes were distinguished. The simplest responses were recorded in subjects with hypersynchronous alpha-rhythm. Analysis of three-dimensional dipole source localization showed that structures of the brainstem, limbic system, and frontal lobes participate in generation of the wave. In all the subjects, the decisive role in response generation was played by the brainstem structures. In persons with hypersynchronous alpha-rhythm, the contribution of the frontal lobes was less pronounced. During "passive" listening of sounds, P300 parameters significantly differed from those observed during counting only in 46% of cases (in persons having no hypersynchronous alpha-rhythm). A simplification of the response shape during "passive" listening was observed in these cases, the area of the maximal response expression was shifted to symmetrical areas of the right-hemisphere, the number of dipole sources reduced due to a decrease in the contribution of the frontal and limbic structures into the response generation.

Adolescent↗
PubMedDate not supplied

[A dipole localization method in analyzing the auditory brain-stem evoked potential].

The localization of generators of brainstem auditory evoked response (BAER) has been studied in one patient using the method of dipole localization based on the spatial distribution of BAER over the surface of the head. It has been found that in formation of all BAER waves the activity of several generators overlaps. It is especially marked for the peaks I', II', III and III'--their potential distribution can not be described by single-dipole model, thus preventing the defining of their generation site. Distribution of potential for other peaks corresponds to the single-dipole model. The coordinates of the equivalent sources of these peaks are in the vicinity of the auditory structures: I--near the distal part of the auditory nerve, II--near the auditory nerve in the place of its entering the brainstem, V--near contralateral auditory pontine structures, V--near lateral lemniscus while V', VI and VI'--near mesencephalic auditory structures.

Adolescent↗
PubMedDate not supplied

[Dipole models of alpha-rhythm generators].

Different hypothesis of the alpha rhythm origin were tested by dipole simulation of the alpha rhythm sources. EEG was recorded during driving photic stimulation in order to increase the signal-to-noise ratio. Models with fixed and moving dipoles were analyzed. Dipole sources were compared with magnetic resonance imaging (MRI) scans to find the exact location of oscillations in brain anatomical structures. A two-level multiple dipole model was found to fit the EEG most adequately. The first level was represented by two oscillators localized in the thalamic reticular nuclei, and the second level is associated with two modality-specific oscillators localized in the respective cortical areas.

Adult↗
PubMedDate not supplied

[Changes in evoked potentials to light in the presence of lesions of the diencephalic and brainstem regions of the human brain].

Evoked potentials (EPs) to light were studied in groups of patients with tumours of basal-diencephalic localization (24 patients) and at the brain-stem level (24 patients), in comparison with 11 normal subjects. In the first group, a decrease of amplitude and increase of response duration were found in the frontal cortical areas, with simultaneous reduction of intrahemispheric differences due to decrease of low-frequency components in the EP spectra by amplitude in fronto-central parts, and of alpha- and beta-frequencies in the occipital parts of the hemispheres. EP changes resulting from brain-stem tumors were more expressed than in the case of cerebellar tumors. In patients with foci causing a pronounced irritation of the brain-stem, a decrease in responses amplitude was observed accompanied by an amplitude lowering of delta- and theta-frequencies in EPs-spectra in the frontal, central and temporal leads, with no changes in the occipital leads. The obtained data testify to functional inequivalence and independence of different EP frequency components suggesting that the methods of studying the EP frequency structure are informative and efficient.

Adolescent↗
PubMedDate not supplied

[Spatial localization of sources of slow EEG activity by the equivalent dipole method].

Coordinates and moments of equivalent sources of various kinds of slow activity--local, generalized and synchronous (delta- or theta-ranges) -- were estimated on a computer on the basis of a model of single equivalent dipole, by the method of the coordinates descent. Investigation of local delta-activity caused by a volume process in the brain shows that its localization coincides with the peripheral zone of the tumour. Localization of the delta-focus enables to indicate its position not only on the surface, but in the depth of the brain as well. The dipole localization method helps to specify the concept of "secondary" slow waves and to differentiate slow activity of total brain-, brain-stem and local nature.

Bone Neoplasms↗
PubMedDate not supplied

[The electroencephalographic correlates of neurological disorders in the late periods of exposure to ionizing radiation (the aftereffects of the accident at the Chernobyl Atomic Electric Power Station)].

EEG mapping and three-dimensional localization of epileptic activity sources together with a neurological analysis were carried out in subjects having taken part in 1986-1987 in the liquidation of consequences of the Chernobyl accident. Experimental group included 40 right-handed 25-45 years-old men having received a radiation dose of 15-51 Ber stated officially. Control group consisted of 20 healthy men. Neurological examination of the patients revealed vegetative-vascular and endocrine dysfunctions as well as diffuse neurological symptoms. EEG of one group of patients (25 persons) was characterized by slow alpha- and theta-band foci and epileptic waves in the central-frontal regions; epileptic sources were localized at the diencephalic level mainly in the midline being shifted to the right hemisphere. In the EEG of another group (15 persons) delta-waves were recorded in the frontal regions at the background of diffuse beta-activity. The sources of epileptic activity of a diffuse character were localized at the basal level of the brain and in the cortex (predominantly) in the left hemisphere. The results obtained together with SPECT mapping and CT data permit to suppose the organic damage of different brain structures (at the cortical and the midline levels) in the patients, with participation of diencephalic structures in the pathological process hypothalamic-hypophysial system being probably connected with adaptive processes in the CNS.

Accidents, Occupational↗