Functional regional asymmetry of the EEG intrahemispheric coherence in dogs during conditioning

Individual features of the regional interhemispheric relations in the brain were studied in dogs during alimentary conditioning. The electrical activity was recorded from symmetrical anterior (frontal and motor cortices) and posterior (visual and auditory cortices) areas of the neocortex. Comparison between the averaged left and right intrahemispheric EEG coherences revealed a dynamic character of interhemispheric relations dependent on the stage of conditioning. Individual features were shown. In a dog with strong type of the nervous system, in the anterior brain regions, the EEG coherence was higher in the left hemisphere than in the right one, whereas, on the contrary, in the posterior regions, the values were higher in the right than in the left hemisphere. In dogs with weak type of the nervous system, there was an inverse relationship. Thus, the spatial organization of the cortical electrical activity in the associative and projection brain areas was different.     

EEG changes in the early postoperative period after excision of tumors of basal-diencephalic location

Changes in the EEG spectral coherence characteristics were analyzed in 60 patients in the early postoperative period after the excision of basal-diencephalic tumors (located in the hypothalamic and thalamic structures) using different surgical approaches (transcallosal, subfrontal, and transnasal). On the first day after surgery, all the patients exhibited a significant decrease in the Δ, θ, and α rhythms compared to the preoperative recordings. Decreased interhemispheric and increased intrahemispheric coherent relations were found simultaneously with changes in the EEG power in patients operated on through the transcranial approach. Within 7–10 days, the pathological structure of the functional relations changed reciprocally. In the case of the transnasal approach, the patients exhibited only an impairment of interhemispheric interaction in the frontocentral areas on the first day after surgery. A decrease in the interhemispheric and an increase in the intrahemispheric coherent relations were determined by the irritation of the pathologically changed hypothalamic and thalamic structures, rather than the dissection of the corpus callosum.     

Spatial organization of biopotentials and original features of visual images

Features of spatial organization of neocortical potentials during mental creating of the original and standard visual images were studied. Intrahemispheric and interhemispheric coherence in different EEG frequency bands and temporal relations between relative changes in the index of linear (correlation coefficient) and non-linear (multiple entropy) processes in different neocortical areas were analysed. Number of decreased coherence values in the high-frequency alpha subband between remote neocortical points during creating of an original image was significantly lower than during creating of a standard image. During creating of the original image, the number of synchronously functioning pairs of neocortical areas and the mean level of linear correlation between the areas were higher, and correlation by the non-linear index, on the contrary, was lower than during creation of the standard image. The correlation between changes in different neocortical areas for both processes during creating of the original image was only positive, and that during creating of the standard image was both positive and negative. The conclusion was made that creative and reproductive types of visual imagination were different in the spatial distribution of coordinated changes in the linear and non-linear processes, mean magnitudes of these changes, and the character of hemispheric interaction. The data on different interhemispheric relations in diagonal and central bilateral directions raise a question about the radial representation of visual imagination.     

Intercentral EEG relationships in regressive and chronic post-traumatic Korsakoff syndrome.]

Dynamic EEG study of patients with posttraumatic Korsakoff's syndrome (KS) with the application of complex analysis methods revealed a complicated pathological structure of the intercentral relations of cortical electrical activity. The interhemispheric EEG coherence between symmetrical frontal cortical areas are sharply reduced, while the intrahemispheric coherence are increased in comparison with the normal values. The proposed technique of segregation of statistically homogeneous spectro-coherent characteristics made it possible to reveal the earlier intercentral EEG relations formed by stable and variable coherence spectra. The structure formed by the stable and variable coherence spectra in KS differs from that reflected in the mean coherence levels. During the KS regression, the EEG coherence between the right and left frontal areas increased to the normal level, and the variable spectra are revealed. In the chronic KS syndrome, the pathological intercentral relations persist, while the variable relations in the frontal areas are absent. A reduction of pathologically decreased intrahemispheric coherence selectively revealed in the right hemisphere during the KS regression and formation of variable relations in this hemisphere point to a leading role of the right hemisphere in development of compensatory processes in KS. The reciprocal relations between the intra- and interhemispheric coherence and coherence dynamics in the theta rhythm suggest that pathological activity in the basal diencephalic structures plays an important role in formation of the pathological EEG pattern in KS.     

The significance of interhemispheric asymmetry in the development of compensatory processes in the human brain

For more precise definition of the role of hemispheric interconnections in mechanisms of human CNS compensation the intercentral relations of the electrical activity of the left and right cerebral hemispheres were studied on physiological model of focal interhemispheric asymmetry. Spectral-coherent EEG characteristics of 36 patients with tumoral damage of one hemisphere were studied in condition of chronic (prior to operation) and acute (early terms of postoperative period) brain decompensation. In was shown that the reorganization of the structure of the EEG intercentral relations correlated with definite stages of CNS compensatory processes and that the character of hemispheric interconnections depended on the lateralization of the damage focus. The primary role was revealed of the degree of the left (dominant) hemisphere preservation in restoration of normal pattern of the interhemispheric asymmetry of the coherence of human brain electrical processes.     

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.     

Changes in the spatial organization of the cortical electrical activity during formation and actualization of a cognitive set to facial expression

Coherence function of the EEG in the bands of 8-13 (alpha rhythm) and 14-25 Hz (beta rhythm) was analyzed in 35 healthy adult subjects during formation and testing of a visual cognitive set to pictures of faces with different emotional expressions. The intra- and interhemispheric coherences of the potentials in the frontal area and coherence between the right frontal and temporal derivation were shown to increase at the stage of set actualization. The results of the analysis confirm the suggestion that the frontal cortical areas are predominantly involved in formation and actualization of the set to facial emotional expression. The conclusion is based on the idea that the spatial synchronization of the brain electrical potentials is an index of the functional relations between the corresponding cortical areas and their cooperative involvement in a certain kind of activity (their simultaneous activation).     

Perception of the emotional component of speech by stuttering children against the background of noise: I. Analysis of the efficiency of the identification of various emotions

The study was devoted to the perception of the speech emotional component by stuttering children under noise impact conditions. The method of study was the evaluation of the probability of an accurate identification of various emotions. Stuttering children were found to be less efficient in identifying all emotions. This fact permitted the assumption that the mechanisms ensuring the identification of emotions against the background of noise by stuttering children form in ontogeny later than that in normally speaking children. Interference immunity of the perception of emotions depends on the emotional coloration of speech. The interhemispheric relations found during the perception of emotions are unstable and, when speech is masked by a noise, acquire the direction that is characteristic of normal children. Thus, the detected ontogenetic features permit one to assume that the establishment of the pattern of interhemispheric relations that is characteristic of normal children is among the reasons of the weakening of stuttering against the background of noise under such conditions.     

Peculiarities of disorders of brain bioelectrical activity spatial-time organization in patients with different consciousness depression after severe head injury

Specific changes of bioelectrical brain activity was found in 27 patients with different level of posttraumatic consciousness depression by the methods of crosscorrelation, coherence and factor analysis of EEG. The changes of activity of morphofunctional systems of intracerebral integrations were revealed partially by decreasing of unspecific activity from brainstem structures reflected with increasing of slow wave activity and decreasing of EEG coherence in alpha- and beta-range. Depression of system organization of interconnections of bioelectrical brain activity in frontal and occipital regions of both hemispheres was also detected, and testified about decreasing of intercortical and thalamocortical brain system action under brain dislocation. The changes of integrative brain system activity, provides interhemispheric interaction, had the specific characted. Our results propose a "facilitation" of activity of system, providing "direct" interhemispheric connections through corpus callosum and other commissural tracts of telencephalon as a sequel of mesodiencephalon structures depression with steady reciprocal, antiphase relations of slow weve activity in symmetrical areas of hemispheres in coma II patients. The data of our research had shown no complete disintegration of system brain activity in coma II patients in spite of consciousness and brainstem reflexes depression.     

The features of system organization of the brain activity during different sleep stages and transition states

Electropoligraphical study of the natural night sleep in 16 adults with the use of correlation, coherent, cluster and factor analysis were used to obtain new data describing the active nature of sleep, which is expressed especially in periods of falling asleep and the transition from one stage to another. It is shown that the process of falling asleep and deeper sleep is accompanied by intense reorganization of cortico-subcortical relations, which is reflected in the dynamics ofcrosscorrelation and coherent estimates of interrelations of biopotentials of the brain. The results of factor analysis of multichannel EEG heterogeneity of the transition process from wakefulness to sleep is manifested in significant changes of I, II and III factors weight during I(B) stage of sleep, which may reflect changes in the degree of contribution of the main integrative brain systems in the reorganization of its integral activity. A considerable increase in the I factor weight (reflecting the generalized modulatory brainstem effect on the cortex), along with a decrease in the balance of factors II and III (associated with organization of fronto-occipital and interhemispheric interactions) clearly indicates a special role of sleep synchronizing influences from the brain stem in the development of this initial stage. Reduction of EEG interhemispheric interrelations in the anterior and inferior frontal areas with the deepening of sleep may be indication of the reorganization of the frontal areas activity associated with the coordinated increasing of inactivation process in the cortex of both hemispheres. Degree of stability of the spatial structure of interregional interactions of different brain cortex areas (according to the analysis of average dispersion of crosscorrelation EEG relations) increases on falling asleep with the onset of stage I(A), but with the transition to the stage I(B) there is a significant increase of instability of values EEG crosscorrelation. With the deepening of sleep the subsequent decrease of the dispersion of EEG crosscorrelations in frontal cortex is revealed. During REM sleep the dispersion levels of inter-regional interactions increases as much as possible, especially for EEG crosscorrelations of posterotemporal and inferiofrontal parts of both hemispheres.     

Interhemispheric asymmetry of the spatial-temporal potentials of the human cerebral cortex under various conditions of the formation of verbal conditioning

It was shown on the basis of electrophysiological data in 60 healthy subjects that the interhemispheric brain asymmetry in the course of formation and actualization of the verbal set depends on the context of the cognitive activity. More complex cognitive activity results in a development of regional interhemispheric differences in the studied characteristics of the spatiotemporal organization of cortical potentials. These differences are most spectacular in the frontal areas of the cortex.     

Spatial synchronization of potentials in the frontal zones of the brain during performance of nominative speech in children

Characteristics of spatial-temporal relations of the frontal zones potentials with those of other brain centres were studied in five- to six-year old children during naming of visually presented objects. EEG cross correlation analysis has shown that during visual perception of familiar objects the correlations of frontal areas with the interior pariental area of the left hemisphere are enhanced; the rhythms of the inferior parietal and occipital zones in the left hemisphere precede the potentials in the frontal area, while in the right hemispere synphasic relations are set up between the frontal and occipital zones. Naming the objects by the appropriate word as compared with rest and showing of the object, leads to enhancement of both intra- and interhemispheric correlations between potentials in the frontal zone and the inferior parietal and temporal zones. The frontal lobe rhythms begin to precede the inferior parietal and occipital potentials and form synphasic relations with the temporal and motor zone potentials in the left hemisphere.     

Interhemispheric EEG Coherence during Rehabilitation of Patients after Severe Craniocerebral Injury

Dynamic clinical and EEG examinations (78 observations) were carried out in 17 patients suffering from severe craniocerebral injury during the course of their rehabilitation. Successful recovery of functions to the point of social and family readaptation was reached in 61% of patients (group I), and in 39% of patients the results were poor (group II). The complex of EEG coherence parameters (six rhythmic bands, mean coherence levels for 26 intrahemispheric and 8 interhemispheric derivation pairs, and the asymmetry coefficient of the EEG coherence) was analyzed in patients in comparison with normal values (20 right-handers). The rehabilitation was most efficient in cases when a certain dynamic sequence of patterns of interhemispheric relations of the EEG coherence was observed. First, a stable formation of right-hemispheric dominance was observed (most expressed in the centrofrontal areas in the range). This asymmetry pattern was phenomenologically associated with the recovery of the emotional sphere and positive dynamics in the motor and autonomic spheres. Later on, formation of the left-hemispheric dominance of the EEG coherence was observed (in the frontotemporal areas in the – ranges. This pattern was associated with complication of the cognitive functions. In the most severe forms of brain damage, the rehabilitation process was accompanied by changes in the interhemispheric EEG coherence with the elements of stealing from one of the hemispheres, which was correlated with clinical dynamics. Different types of the dynamics of reactive changes in the EEG coherence were revealed in patients of the two groups: successive formation of a generalized and then local modally specific reaction to afferent stimuli was observed in group I, while the generalized type of reactivity persisted in group II until the end of rehabilitation. It is suggested that the different sequence of formation of the interhemispheric EEG coherence reflects the involvement of different brain regulation systems in different orders into the integrative activity, i.e., some specific features of the rehabilitation process.     

Functional Connectivity in the Brain Estimated by Analysis of Gamma Events

It is known that gamma activity is generated by local networks. In this paper we introduced a new approach for estimation of functional connectivity between neuronal networks by measuring temporal relations between peaks of gamma event amplitudes. We have shown in freely moving rats that gamma events recorded between electrodes 1.5 mm apart in the majority of cases, are generated by different neuronal modules interfering with each other. The map of functional connectivity between brain areas during the resting state, created based on gamma event temporal relationships is in agreement with anatomical connections and with maps described by fMRI methods during the resting state. The transition from the resting state to exploratory activity is accompanied by decreased functional connectivity between most brain areas. Our data suggest that functional connectivity between interhemispheric areas depends on GABAergic transmission, while intrahemispheric functional connectivity is kainate receptor dependent. This approach presents opportunities for merging electrographic and fMRI data on brain functional connectivity in normal and pathological conditions.     

Disorders of the spatiotemporal organization of the brain’s bioelectrical activity in patients with different depressions of consciousness after severe head injury

Specific changes in the bioelectrical activity of the brain have been found in 27 patients with different levels of posttraumatic consciousness depression (stupor, spoor-coma I, coma II) by the methods of cross correlation, and coherence and factor EEG analysis. The changes in activity of the morphofunctional systems of intracerebral integrations were expressed partly in a decrease in the nonspecific activating effects from brainstem structures, which was reflected in an increase in the slow wave activity along with a considerable decrease in the level of EEG coherence in the α and β ranges. The observed depression of the system’s organization of the interrelations of the bioelectrical brain activity in the frontal and occipital regions of both hemispheres could be due to a decreased activity of the associative systems of intercortical and thalamocortical integration. The results suggest a certain facilitation of the activity of the system providing direct interhemispheric connections through the corpus calossum and other commissural tracts of the telencephalon as a consequence of the depression of the mesodiencephalon structures (which normally largely contribute to the synergistic interhemispheric interaction via synchronous ascending effects on the cortex of both hemispheres). This results in steady, reciprocal, and almost antiphase relations of slow wave activity in symmetrical areas of the hemispheres.     

The locked-in patient and the characteristics of the electrical activity of his brain

"Locked-in" state differs from the known states characterized by the motor activity blockade, preservation of conscience of speech contact, despite the fact that connection with outer world during this state is limited only by vertical movements of eyes and eyelids in response to speech signals. Three "locked-in" men were studied at different stages of development of this state. Spectral-coherent analysis of the EEG was conducted. The most typical for the developed state of the "locked-in" man is a uniform change of the intercentral EEG relations. In the motor areas of the cortex alpha-activity and its links are not formed (coherence in alpha-range is zero) while high and low frequencies are coherent. In the visual areas, in contrast, the alpha-rhythm is coherent. Distinct interhemispheric asymmetry of coherent connections appears. In the right hemisphere a decrease of coherence level is sharp and even, in the left one--in occipito-temporal parts the level remains close to norm, while in the frontal parts of the cortex it decreases.     

The ECoG of rats with genetic catalepsy]

Electrographic study was carried out in Wistar rats and the rats of genetical catalepsy (GC) strain. In contrast to Wistar rats epileptiform activity was observed in ECoG of GC rats being enhanced at the transition to a cataleptic state. Analysis of spectra and coherence of EEG revealed the presence of interhemispheric brain asymmetry in all the rats. In some frequency bands in GC rats inversion of interhemispheric asymmetry was found, which had been characteristic for Wistar strain. The highest interhemispheric synchronization of biopotentials was observed in the frontal cortical areas in GC rats and in the occipital areas in those of Wistar strain.     

Reorganization of interhemispheric interactions during verbal-mental activity aimed at synthesis of words and sentences

Correlation and coherence analyses of multichannel electroencephalogram (EEG) recordings from 18 subjects (mean age 25 years) were used for investigating the reorganization of systemic interactions between bioelectric potentials of the cortical areas of both hemispheres (20 EEG derivations) during verbal-mental activity connected with generating verbal units from simpler components. When generating either words from aurally presented phonemes or sentences from a set of words, the subjects exhibited specific changes in the spatial structure of the statistical relationships in the EEG, with a significant increase in the interhemispheric interactions. During performance of both tasks, the changes in the interhemispheric interactions were most pronounced in the temporal, temporo-parieto-occipital (TPO), inferofrontal, and occipital areas of both hemispheres. Phonemic synthesis was associated with a more marked increase in the contralateral interactions in the left hemisphere, and generating sentences from words, in the right hemisphere. The coherence analysis of the EEG showed the greatest changes in the Δ, ?, and β frequency bands, with rather slight changes in the α frequency band. For all frequency bands, changes in the EEG coherences were the greatest in Wernicke’s and the TPO areas of the right and left hemispheres during the performance of both tasks, especially during the phonemic synthesis. These findings suggest that neurophysiological processes underlying mental generation of words and sentences require coordinated activity of the left and right hemispheres, which is accompanied by an increase in the interhemispheric interactions in the EEG, especially in the temporal, inferofrontal, and TPO areas.     

The functional testing of the interhemispheric asymmetry in the spatial organization of rabbit cortical potentials]

Interhemispheric asymmetry was studied of spatial-temporal potentials organization (STPO) of the cortex in non-fixated animals in the states of deep rest, behavioural activity and in the transition period between them. Despite the intrahemispheric differences of the STPO in each of these states, interhemispheric divergences in the character of reconstructions of momentary topograms of the cortical potentials, recorded at 24-channels leading, are limited by 35% of the epoch analysis time. Comparison of the dynamics of intrahemispheric changes of topograms of cortical potentials in the left and right hemispheres in the states of rest and activity revealed a narrowing of temporal period of the absence of resemblance in reconstructions of successive topograms of the left and right hemispheres in comparison with transition processes. In the phase of rest the interhemispheric conjugation of spatial reconstructions in topograms became lowered mainly because of the disturbances of monotony of changes of their reliefs in one of the hemispheres in turn. In the active phase, deviations from STPO of the cortex, characteristic of the state of rest, were met more frequently in the right hemisphere; in that case oscillations of the topograms general mean level connected with the activity of non-specific activating subcortical brain system acquired a significant role in regulation of interhemispheric relations. Presence of interhemispheric resemblance of reconstructions of topograms reliefs in the active phase, despite the tendency to its lowering in comparison with the rest, testifies to the contribution also of the intracortical processes to the interhemispheric spatial synchronization of the cortical potentials in this state.     

Spectrum and coherent characteristics of bioelectric activity of the brain in women with normal and complicated pregnancy

Spectrum and coherent EEG analysis was performed in 86 pregnant women on the 35-36th week of gestation. It was shown that functional interhemispheric brain asymmetry is a sensitive index of normal and complicated gestation. It was found out that activation prevailing in the central and temporal brain areas contralateral to the side of placenta localization in the uterus was characteristic of the normal pregnancy. The development of gestation complications was accompanied by the inversion of interhemispheric asymmetry of EEG activation. It was suggested that correlative properties of bioelectric brain activity in women with normal gestation are an indicator of the left-hemispheric dominance of brain centers in the integration process.