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Biomedical subjects

E L Masherov

Publications and source records attributed to E L Masherov.

9 recordsLinked to original sources
PubMed2003

[Component P300 of acoustic evoked potential in patients with local brain lesion].

The aim of the study was a comparative analysis of spatial-temporary organization of P300 acoustic evoked potential (AEP) in patients with local lesions of the brain stem, frontal and temporal structures in the situations of "passive" listening to sounds and their active recognition (a count). Specific changes of P300 parameters were distinguished in each group. The peak-temporary P300 parameters--latency increase, decrease of amplitude and tendency to the decrease of half-cycle--were similarly changed, irrespective of brain damage topography. A degree of the changes correlated with a level of functional acoustic evoked potential decompensation. In relation to pathologic process location, the topographical P300 AEP features were more specified, comparing to peak-temporary parameters. An existence of two systems for P300 generation at "active" counting and "passive" listening was suggested. In "passive" listening, a response is mostly determined by intact left frontal lobe and middle-stem structures but in "active" counting--by intact right frontal lobe or lobes and limbic system structures (hippocampus).

Adult↗
PubMedDate not supplied

[Visual evoked potentials and the P300 component in different courses of the posttraumatic vegetative state].

The late latency components of visual evoked potentials (VEP) and the component P300 AEP were analyzed to evaluate their informative value in the process of mental function restoration in patient after long-term traumatic coma. VEP components with latencies of 70 to 320 msec were studied in 24 patients. Topographical mapping of the power of the study VEP components and components P300 was made by the peak amplitude. Long-term VEP components and component P300 were examined by the method of three-dimensional localization of equivalent dipole sources. In 16 patients with positive tendencies in the condition there was a stable localization of the maximum VEP power in the parietal, sagittal, and occipital regions, component P300 showed its maximum amplitude in the central and parietal regions in the left hemisphere. Eight patients with negative tendencies in the status had the maximum VEP and component P300 in the frontal and temporal regions, predominantly in the right hemisphere. The paper shows it important to evaluate not only time-amplitude parameters and analyzes the tomographic features of its formation in dynamics.

Acoustic Stimulation↗
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

[The electroencephalographic correlates of a disorder in higher cortical functions in local lesions of the hypothalamic area].

In order to reveal correlations between disturbances in higher cortical functions and characteristics of electrical activity 70 patients with pathological foci in the hypothalamic regions were examined using computer data processing. Destruction of the normal intercentral relations between EEG rhythms develops under the influence of the hypothalamic focus. The process builds up with the aggravation of cortical disorders (mnestic, emotional-affective, consciousness oppression with sleep inversion). General decrease of EEG coherence is observed with the highest destruction of correlations in the frontal cortical areas. The structure of high-frequency alpha-rhythm becomes deranged even in slight cortical disorders, its coherence decreases predominantly in the frontal cortical areas. With intensification of the pathological process in the focus, the stage of delta-rhythm coherence increase is observed and at the background of general destruction of correlations new, pathological intercentral relations develop. Using a BRAINLOC computer technique "sources" of the delta- and theta-activity have been localized in the medio-basal brain regions. The area of localization is specific for hypothalamic lesions. The "source" is mostly expressed in the slightest pathology of higher cortical functions. With aggravation of the process in the hypothalamic pathological focus and further derangement in the cortical functions expression of the "sources" reduces up to their complete disintegration in coma.

Adenoma↗
PubMedDate not supplied

[Foci of pathological activity in the human brain and their influence on the spatial-temporal relationships of the EEG].

EEGs of 51 patients with focal brain lesions (tumor localized in brain hemispheres) were analyzed. Coherence functions were calculated between the EEG recorded from the intact and lesioned hemispheres and three-dimensional analysis of the delta-wave "source" localization was conducted. The revealed delta-wave "sources" localized in the perifocal region of the lesioned hemisphere demonstrated its dynamic properties and a tendency for fluctuations. Changes in the delta-wave "source" pattern were correlated with the EEG coherence values neither in the lesioned nor in the intact hemisphere. The focus of pathological activity produced the changes in EEG coherence and its interhemispheric asymmetry. In the majority of cases (72%), the mean level of intrahemispheric coherence at the side ipsilateral to the pathological focus was lower than the normal mean level, and the mean level of EEG coherence in the intact hemisphere was increased.

Brain↗
PubMedDate not supplied

[The P300 component of the auditory evoked potential in the posttraumatic vegetative state].

The dynamic studies of P300 component of the acoustic evoked potential were conducted in 12 patients in posttraumatic state of the autonomic system. The amplitude and time parameters of P300 were analyzed, its spatial distribution over the cortex, and features of generation. The obtained results were compared with the normative data. Significant changes in P300 in comparison with the normal characteristics were revealed in patients with the absence of conscious mental activity. These changes were maximally expressed when the state of patients was irreversible. In case of patients' outcome from the studied state the amplitude-temporal and topographic response characteristics tended to normalization but did not reach it completely. The obtained results allow us to consider the P300 component as one of the most informative indices in consciousness recovery after severe brain injury.

Adolescent↗