Correlation between electrical activity in symmetrical regions of the cerebral cortex and unilateral lesions]

Functional interrelations between cerebral hemispheres, and particularly, between their symmetrical areas, were studied during compensatory processes in patients with tumours localized in one of the hemispheres. Analysis of spontaneous electrical activity before the operation on the tumour revealed several types of interhemispheric relations. The existence of a sharply pronounced pathological activity in one hemisphere, testifying to inactivation of cortical cells, is, as a rule, accompanied by activation in the intact hemisphere, especially in the areas symmetrical with those injured. In cases of less pronounced pathology, with partial retention of activity of the cortical cells in the injured areas of the affected hemisphere, a lesser degree of activation is observed in the intact hemisphere. The data point to a development of substituting-compensatory processes in the areas of the intact hemisphere symmetrical with the injured ones and to the possibility of testing the processes electrophysiologically.     

Reflection in the electrical activity of the brain of the activities of the mechanisms regulating the functional state

On the basis of analysis of the results of author's studies and literature data, theoretical notions are developed, according to which spatial-temporal organization of cortical biopotentials is a result of activity of nonspecific different level systems subtly regulating current alertness in conformity with needs of the actual and forthcoming activities. In the hierarchy of regulating systems, in conditions of alertness, nonspecific thalamic and midbrain system is leading. Activity of these regulation levels provides in alertness for formation and destruction of functional neuronal ensembles which realize elementary informational transformations. The role is emphasized of asynchronous processes in the central nervous system activity.     

The intercentral relations of cortical bioelectrical activity in the human brain after surgical interventions on brain stem formations]

In the process of dynamic study of cortical bioelectrical activity and indices of its intercentral interaction in 52 neurosurgical patients with focal lesion on the brainstem level, the dependence was shown of the CNS reactions to the operative intervention on the character and degree of damage. Variants were described of compensatory neurodynamic reconstructions of electrical processes in observations with transient, stable and irreversible pathological foci of brainstem localization.     

Steroids and electrical activity in the brain

Corticosteroid hormones can enter the brain and bind to two receptor subtypes: the high affinity mineralocorticoid receptor (MR) and the glucocorticoid receptor (GR) with approximately 10-fold lower affinity. Under physiological conditions the degree of receptor occupation will range from a predominant MR occupation (at the beginning of the inactive period, under rest) to concurrent activation of MRs and GRs (at the circadian peak and after stress). With in vitro electrophysiological recording techniques we observed that neuronal excitability in the CA1 hippocampal field is under a long-term control of MR- and GR-mediated events. The predominant occupation of MRs is associated with a stable amino acid-carried synaptic transmission; calcium- and potassium-currents are small, as are the responses to biogenic amines. Occupation of GRs in addition to MRs results in a gradual failure of CA1 neurons to respond to repeated stimulation of amino acid-mediated input; ionic conductances and responses to biogenic amines are large. In general, electrical properties recorded when both MRs and GRs are unoccupied (i.e. after adrenalectomy) resemble the responses observed when both receptor types are activated. The corticosterone dependency of electrical properties is thus U-shaped. We conclude that MR occupation may be responsible for the maintenance of information processing in the CA1 field and the stability of the circuit. Additional activation of GRs will initially suppress synaptic activity, but may eventually result in an increased instability and even vulnerability of the neuronal networks.     

Dependence of the organization of human brain electrical activity on hemispheric dominance

In healthy subjects, in a state of relative rest, with different individual profiles of asymmetry (20 right-handed and 10 left-handed subjects), a greater conjunction of electrical brain processes (estimated by mean EEG coherence levels) has been found in the dominant hemisphere as compared to the subdominant one, more distinctly expressed in the right-handed subjects. The maximum degree of interhemispheric asymmetry of the EEG coherence is observed in the posterior associative cortical areas. Specific interhemispheric theta-range differences are revealed as compared with other EEG frequency bands. Greater values are obtained of the correlation of the EEG symmetrical hemispheres points in the whole frequency band and in alpha- and beta-ranges in the right-handed subjects than in the left-handed ones.     

Electron-cytochemical study of ATP-ase activity in the brain after death]

The lead method was applied to determine the localization of the ATP-asic activity in the rat and human brains at different periods after death. This activity was revealed in the cytoplasm of the cells, chromatin and the nucleolus, and also in the synaptic terminals. In the vascular capillaries the product of reaction was localized in the basal layer and on the cytomembrane of the endothelial cells. The results obtained pointed to a good preservation of the ATP-asic activity in the postmortem brain.     

The spectral correlation characteristics of the brain electrical activity in the rabbit during thirst]

Spectral-correlation analysis of the summate electrical activity of a number of subcortical structures of rabbit brain, having, by literature data, a relation to drinking behaviour showed that the increase of drinking excitability, induced by water deprivation was accompanied by definite reconstruction of biopotentials. In electrical activity of the studied structures, the spectrum power, as a rule, decreased (except in the paraventricular nucleus), and a definite structure of coherent connections between the subcortical and cortical potentials was established. Among the studied subcortical formations, structures (anterior hypothalamic area, lateral preoptic area, medial preoptic area, paraventricular nucleus) could be singled out where reconstructions of spectral characteristics of biopotentials took place most regularity, and the electrical processes in which were characterised by coherence index by an increase of spatial interconnection with the neocortex potentials, what allows to consider them as most significant for organization of drinking excitation.     

The status of conditioned reflex activity in cats after unilateral vestibular neurotomy]

In chronic experiments on 6 cats the influence was studied of unilateral vestibular neurotomy on conditioned, oculographic and electrocardiographic reactions. In operated animals appeared sharply expressed posetonic and oculomotor disturbances, lowered general functional brain state, what was manifested in an increase of specific weight of slow spindle-shaped rhythmics and lowering of the conditioned activity level. Against the background of the lowered functional brain state interhemispheric asymmetry developed with relative predominance of the contralateral hemisphere, what was reflected in electrocorticographic manifestations and disturbance of conditioned spatial differentiations. Significance is grounded of the appearing interhemispheric asymmetry in the development of disturbances of spatial analysis in operated animals.     

The spectral characteristics of the electrical activity in the rabbit brain during the hunger dominant]

By means of daily alimentary deprivation the dominant of hunger was created in rabbits. In response to acoustic stimuli summational swallowing and chewing movements appeared. Spectral analysis of the electrical brain activity showed the presence of primary dominant focus zone (lateral and ventromedial hypothalamus), characterized by an increase of spectrum power in delta-range while in the orbito-frontal, sensorimotor, parietal cerebral cortex, in the medial and lateral preoptic hypothalamic zones the power of biopotentials spectrum decreased within the whole analyzed frequency range.     

The spectral correlations of human brain electrical activity (the EEG) in the alpha-rhythm range occurring while performing latent inhibition]

Changes in perception of a stimulus and impairment of retrieval of memory trace resulted from the stimulus loss of novelty are called the latent inhibition (LI). The present study was undertaken to investigate the human LI using the analysis of changes in frequency power and coherence of the alpha rhythm. The results indicate that the loss of novelty of a stimulus is accompanied by a significant increase in the power of the upper alpha in the frontal regions of the right hemisphere and temporal regions of both hemispheres resulting in an impairment of memory retrieval in the frontal regions. Analysis of coherence changes revealed the reduction of interaction between the right temporal region and anteriofrontal, temporo-occipital, and right parietooccipital regions in response to administration of the conditioned words in comparison with the control ones. The findings suggest that the LI is a manifestation of the more general physiological process--the hidden inhibition.     

Alterations of spectral parameters of rat brain electrical activity after sciatic nerve section

Changes in electrophysiological brain characteristics accompanying the development of neurogenic pain syndrome induced by transsection of sciatic nerve were analyzed. At the maximum pain syndrome 3 weeks after the deafferentation, a reorganization of the brain electrical activity was observed in the limbic structures (hippocampus, amygdale, and nucleus accumbens), frontal cortex, and the caudate putamen. An increase in the relative spectral power of the delta and alpha bands and a decrease in the relative power of the beta2 band (as compared to baseline activity) took place. Alteration of the electrical activity in the limbic structures did not depend on manifestations of the neurogenic pain syndrome (autotomy). The increase in the relative spectral power of the alpha-band activity in all the structures under study suggests the involvement of the reticular thalamic nucleus in pathogenesis of neurogenic pain syndrome.     

Reflection of cortical activation pattern in the human EEG phase structure

Investigation was fulfilled on healthy subjects (22) and on outpatients (62). The EEG by the standard scheme as recorded at resting with open and closed eyes and under different functional loads. These records were processed in accordance with the EEC phase structure with the aid of computer animation technology. The main idea of the phase structure technology consists in rejection of one supporting lead. Time shifts were measured only between two neighbouring electrodes, so that the oscillations under comparison were always highly coherent. Time errors were evaluated according to crosscorrelation function maximum shift. The differences between high- and low-frequency EEG rhythms were shown to be only quantitative from the phase structure viewpoint. Qualitatively, the rhythm properties were equal and came to slow (second) phase structure oscillations. Low frequency activity compared to high frequency one was characterized by greater phase shifts from electrode to electrode. Phase shifts of potentials are forming the structure which, as a whole, is very similar in different people and is reproduced in different states. Initial EEG waves appearance is statistical linked with main sensory projections: visual (occiput), auditory (temples) and somatic (parietal region) with addition of frontal region. Redistribution of phase leadership in favor of occipital pole and to both temporal regions when eyes are open is described. It is apparently dependent on the sensory surge level from thalamus to a given cortex region. Phase gradient direction seems to reflect the cortex current density gradient which is parallel to surface. It can be used for localization of compact sources lying near to cortex.     

Compensatory recovery of vagal control of hemodynamics after unilateral vagotomy

This study investigated whether each part of the heart is evenly innervated by the left or right vagus and observed the mechanism of compensatory recovery after unilateral cervical vagotomy. HR, BP, LVSP and +/-dp/dt max all decreased one week after left vagotomy, whereas only BP and -dp/dt max decreased one week after right vagotomy. Western blot analyses revealed that the expression of M(2) receptors in the left atrium and left ventricle was upregulated after subacute (1 week) left/right vagotomy. However, significantly more cholinesterase-positive nerves in LV and RV were seen one week after unilateral vagotomy compared to the sham-operated group. In addition, baroreflex sensitivity was increased after subacute right vagotomy. The decreasing effects of ACh (0.5 microg/kg) on LVSP and +/-dp/dt max (but not on HR and BP) were facilitated by subacute unilateral vagotomy. Our present experiments indicate that 1) the working myocardium is innervated bilaterally by the vagus, 2) ventricular contractility is influenced more by denervation of the left than the right vagus and 3) up-regulation of M(2) muscarinic receptors in the left heart, increase of cholinergic nerves, and high baroreflex sensitivity could be involved in the mechanism of compensatory hemodynamic recovery via contralateral vagus overactivity, thereby amplifying contralateral vagal activity and decreasing cardiac contractility.     

Crossintervalograms for analysis of electrical activity of the brain

A method of construction of crossintervalograms for electroencephalograms is proposed. Particular points or EEG fragments of particular shape are used as time-locked events, and the intervals between these reference points are analyzed. The method is theoretically substantiated. Examples of crossintervalograms constructed for EEG extrema and derivative EEGextrema are given. The information validity of these crossintervalograms is demonstrated and their features are indicated. Comparison crossintervalograms with crosscorrelograms is performed. The possibilities of further development and applications of a method are specified. It is suggested that the method will be useful for investigation of operative interaction of brain subsystems.     

Evoked frequency stabilization in the electrical activity of the cat brain

In this study, our previous results on the important relation between EEG and EPs were extended by experiments with chronically implanted and freely moving cats, which had electrodes at the acoustical cortex, inferior colliculus and reticular formation. During the experiments the frequency stabilization upon sound stimulation was shown in the frequency domain by comparison of the pre-stimulus power spectra and post-stimulus amplitude frequency characteristics. Comparative frequency domain analysis of about 75 EEG-EPograms (sample of spontaneous activities just prior to stimulation and single evoked potentials following the stimulation), which were recorded from all the brain nuclei mentioned above and from each of the 11 cats, was performed as follows: 1) Power spectra of the EEG-records prior to stimulus were evaluated. 2) Instantaneous frequency characteristics of single EPs were obtained by the Fourier transform. 3) Distribution of the amplitude maxima of the EP-frequency characteristics and the distribution of the EEG-spectral peaks were compared by plotting two types of histograms containing relevant spectral peaks before and after the stimulation. In a frequency range between 1–1000 Hz, the frequency distribution of the EP records from RF and IC were accumulated in narrow discrete frequency channels, whereas, the distribution of the spectral peaks of the EEG depicted frequency spread in broad channels. The frequency stabilization of the EP records from GEA, in the alpha frequency range, was also observed. This effect was described by a factor which we called as the Frequency Stabilization Factor. The results presented in this study showed that the frequency stabilization of the brain's electrical activity induced by sensory stimulation displayed a fluctuation leading to frequency stabilization factors between 0.95 and 5.00. The frequency stabilization and relevant power enhancement upon stimulation strongly support our contention that evoked potential results from the frequency stabilization of the spontaneous activity, triggered by stimulation.Supported by Grant No. TAG-345 of the Scientific and Technical Research Council of Turkey