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.     

EEG markers of the stabilotraining effect during the rehabilitation of patients with posttraumatic Korsakoff’s syndrome

Nine patients with posttraumatic Korsakoff syndrome (KS) were examined before and after a rehabilitation course of feedback stability training (ST) using EEG, posturographic and clinical tests (with the FIM and Mayo Portland scales used for estimation). During 7 to 12 sessions, the patients tried to perform static and motor tasks. A group of 18 healthy subjects were examined to provide standard parameters. The results demonstrated a disturbed spatiotemporal EEG pattern in patients with KS before ST in the form of a reduced coherence for short derivation pairs (intrahemispheric, interhemispheric, and diagonal ones) in frontal and parietooccipital areas. Analysis of specific EEG rhythms demonstrated the maximum decrease in coherence in the α band (with the aforementioned regional specificity) and for long diagonal pairs (between the left frontal and right parietooccipital areas). The ST course was accompanied by KS regression (according to clinical scales and posturographic study); an original increase in EEG coherence, especially that of α waves, was recorded in the occipitoparietal and central frontal areas of the right hemisphere; a subsequent increase in coherence of the frontal areas in both hemispheres was observed. Late after the ST course, further positive changes were characteristic of the EEG spatiotemporal pattern. However, comparison with standard data suggested incomplete recovery of various coherence parameters: hypertrophied coherence in intrahemispheric pairs and still reduced values in interhemispheric derivations. This EEG pattern suggested incomplete KS regression, which was confirmed by clinical data.     

The role of cerebral regulatory structures in the formation of human EEG

This article generalizes the results of many years’ studies of the EEG of patients with tumorous lesions in the diencephalic, brainstem, and limbic structures, which fulfill the regulatory function in ensuring integral brain activity. The specific features of the inclusion of individual structures under investigation in the organization of the intra- and interhemispheric relations of cortical biopotentials were demonstrated against the background of diffuse changes in the biopotentials that reflect the systemic character of neurodynamic reorganizations when the regulatory brain structures are involved in the pathological process. This study expands the idea of the predominant functional connection of the diencephalic structures with the right hemisphere and brainstem structures with the left one with determination of the regional specific features of changes in the intrahemispheric EEG coherences. The distinguishing features of intercentral relations when the limbic structures are involved in the pathological process show similarity with the neurodynamic reorganizations in patients with lesions in both diencephalic and (even more so) brainstem structures. Universal elements were detected in the formation of integral adaptive reactions of the brain with lesions in its regulatory structures, which reflects their close functional interaction and makes it possible to consider them the individual links of an integral regulatory system. The study revealed reciprocal changes in various forms of electrical activity, which reflects reciprocation of interaction of individual regulatory structures. This is one of the EEG equivalents of the formation of adaptive-compensatory cerebral reactions. The specificity of influence of the studied regulatory structures are clearly seen in situations of their morphofunctional isolation observed during cerebral coma. In these conditions, when the cortex is functionally inactive, the authors demonstrated the dynamic character of changes in interhemispheric asymmetry, which reflects the dominance of individual links of the regulatory system playing the role of supreme regulator of life support of the body in critical states.     

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.     

Spectral-correlation characteristics of the electrical activity of the brain of the rabbit in a state of calm wakefulness

Inter- and intrahemispheric relations of electrical activity of the pre-motor, sensorimotor (representation of forelimb and blinking) and visual zones of rabbit's cerebral cortex in calm alertness was studied by method of spectral-correlative analysis. Mean coherence levels of the EEG of tested hemispheric symmetric points and symmetric pairs of leads in the left and right hemispheres were characterized by a high temporal stability in the state of calm alertness and during sensory stimulation. A comparison of mean coherence values of EEG in symmetric leads, revealed a tendency to left-side dominance of statistical bonds of electrical processes. A tendency was shown towards interhemispheric asymmetry by mean parameters of EEG power spectra: the left hemisphere of the rabbit is characterized by a lower mean frequency of electrical activity and a more narrow effective frequency of the spectrum.     

Intercentral Relations of the Human EEG during Listening to Music

Different musical styles and intensities produce characteristic patterns of changes in the correlation of neocortical biopotentials. Classical music of three intensities and rock music of medium and high intensities were shown to produce asymmetry in the pattern of coherence (Coh) of the cortical activity of listeners: intrahemispheric Coh in the right hemisphere increased, while a decrease in the EEG synchronization prevailed in the left hemisphere. A focus of Coh integration, most pronounced for the γ frequencies, was formed during listening to both classical and rock music (except rock music of a low intensity). Listening to rock music of a low intensity substantially increased the probability of a decrease in intra- and interhemispheric Coh in both hemispheres, which was pronounced in all frequency bands. Listening to rock music changed interhemispheric Coh in a greater percent of cases than listening to classical music.__________Translated from Fiziologiya Cheloveka, Vol. 31, No. 4, 2005, pp. 27–32.Original Russian Text Copyright © 2005 by Sakharov, Davydov, Pavlygina.     

Intracerebral EEG functioning as a reflexion of the systemic brain organization in norm and pathology

The authors summarized the EEG findings and defined the nature of intercentral EEG relationships in different functional states of healthy subjects and patients with organic cerebral pathology based on coherence analysis. The EEG features typical of healthy subjects were identified: an anterior-posterior gradient of the mean coherence and the character of cortical-subcortical relationships in the anterior cerebral structures. Right- and lefthanded subjects showed the frequency and regional differences in EEG coherence, which reflected, mainly, specific intracortical relationships. Development and regression of pathologic signs in right- and lefthanded patients with organic brain lesions are thought to be determined by these differences. As distinct from cortical pathology, lesions of regulatory structures (diencephalic, brainstem, and limbic) were shown to produce more diffuse changes in intercentral relationships with a tendency to reciprocity. Intercentral relations, including their interhemispheric differences, varied with changes in the functional state of healthy subjects (increase and decrease in the level of functioning). A certain time course of changes in intercentral relationships was also revealed in patients with organic brain lesions during recovery of their consciousness and mental activity. Changes in the dominance of activity of individual regulatory structures are considered to be one of the most important factors that determine the dynamic character of EEG coherence.     

Electrophysiological Correlates of Morphological Neuroplasticity in Human Callosal Dysgenesis

In search for the functional counterpart of the alternative Probst and sigmoid bundles, considered as morphological evidence of neuroplasticity in callosal dysgenesis, electroencephalographic (EEG) coherence analysis was combined with high resolution and diffusion tensor magnetic resonance imaging. Data of two patients with callosal agenesis, plus two with typical partial dysgenesis with a remnant genu, and one atypical patient with a substantially reduced genu were compared to those of fifteen neurotypic controls. The interhemispheric EEG coherence between homologous nontemporal brain regions corresponded to absence or partial presence of callosal connections. A generalized coherence reduction was observed in complete acallosal patients, as well as coherence preservation in the anterior areas of the two patients with a remnant genu. jThe sigmoid bundles found in three patients with partial dysgenesis correlated with augmented EEG coherence between anterior regions of one hemisphere and posterior regions of the other. These heterologous (crossed) interhemispheric connections were asymmetric in both imaging and EEG patterns, with predominance of the right-anterior-to-left-posterior connections over the mirror ones. The Probst bundles correlated with higher intrahemispheric long-distance coherence in all patients. The significant correlations observed for the delta, theta and alpha bands indicate that these alternative pathways are functional, although the neuropsychological nature of this function is still unknown.     

Post-radiation effect on the interhemispheric asymmetry in EEG and thermography characteristics

Complex analysis of EEG and thermographic parameters carried out in 10 healthy subjects and 34 patients, Chernobyl clean-up participants revealed a correlation between EEG and brain temperature changes in the baseline state and during mental arithmetic. During cognitive activity the maximal increase in the average EEG coherence and temperature shifts in healthy subjects were observed in the left frontotemporal and right parietotemporal areas. In patients changes in both parameters under study were most pronounced, the interhemispheric relations were impaired. The visual analysis revealed "flat" and "hypersynchronous" EEG types in patients. The dominant pathologic activity in the betal range indicative of mediobasal and oral brainstem lesions was characteristic of the flat EEG. This type of activity was observed in 60% of patients. In these cases, a general decrease in EEG coherence and temperature was most pronounced in the left hemisphere. The hypersynchronou EEG type (40% patients) was characterized by paroxysmal activity in the theta and alpha ranges suggesting diencephalic brain lesions. In these cases, EEG coherence and temperature were more variable; changes in the right hemisphere were significant, be it increase or decrease. Our complex approach to investigation of brain activity in different aspects seems to be promising in estimation of the brain functional state both in healthy persons and patients in remote terms after exposure to radiation. The specific hemispheric temperature changes revealed in Chernobyl patients especially during cognitive activity can be the sequels of postradiation disorders of vascular neuro-circulation. The EEG findings suggest subcortical disorders at different levels (diencephalic or brainstem) and functional failure of the right or left hemispheres in remote terms after exposure to radiation.     

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.     

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.     

Electroencephalographic characteristic of cognitive-specific alerting attention in verbal learning--III: Localized characteristics of EEG spatial synchronization

Electroencephalograms (EEG) were recorder in 19 standard derivations in 88 healthy subjects, while they were in the states: rest with eyes open; memorization (learning) of verbal bilingual semantic pairs (Latin and Russian languages); the retrieval of the rote information from memory (control). We compared estimates of EEG coherence in these states for the frequency bands theta (4-7 Hz), alpha-1 (7-10 Hz), alpha-2 (10-13 Hz), beta-1 (13-18 Hz), beta-2 (18-30 Hz), gamma (30-40 Hz). When compared with the rest most strongly expressed: for memorization a decrease of coherence in the pairs of derivations from frontal and central areas of the cortex in the EEG frequency bands; for retrieval an increase of coherence in interhemispheric derivation pairs of pariental-occipital region in majority of the frequency bands. For the retrieval also increases of coherence in the beta2 and gamma bands, along with coherence decreases at low frequencies take place in pairs formed by derivations from the parieto-occipital region with derivations from the frontal and the central ones. Dynamics of EEG coherence in comparisons of memorization and retrieval from the rest and each are expressed significantly more in the interhemispheric and crosshemispheric pairs of derivations than in the intrahemispheric pairs. Revealed topographic specificity of the dynamics of EEG coherence by changing the states is considered in terms of ideas about cognitive-specific forms of sustained goal-directed mental attention.     

Hemispheric organization of verbal memory functions in seasonal winter depression: electrophysiological analysis

Spatial organization of EEG power and coherence during memorization of dichotically presented lists of words were studied in patients with winter depression (N = 17) and control subjects (N = 22). In contrast to the control subjects, the depressed patients were characterized by the higher theta power in the right parietal and posterior temporal regions and the dominance of the alpha 2 in the left midfrontal area. The patients also differed in the lower theta 2 coherence in the left hemisphere and lower alpha 1 coherence in the right hemisphere. These effects showed different intrahemispheric distribution. The interhemispheric EEG coherence in the theta 2 range between the frontal areas and alpha 1 coherence between the left frontal and right posterior areas was lower in the patients than in the control subjects. Verbal-emotional interaction in depressions are discussed.     

Decision of mathematical logical tasks in sensory enriched environment (classical music)

The time of a decision of mathematical logical tasks (MLT) was decreased during classical musical accompaniment (power 35 and 65 dB). Music 85 dB did not influence on the process of decision of MLT. Decision without the musical accompaniment led to increasing of coherent function values in beta1, beta2, gamma frequency ranges in EEG of occipital areas with prevalence in a left hemisphere. A coherence of potentials was decreased in EEG of frontal cortex. Music decreasing of making-decision time enhanced left-sided EEG asymmetry The intrahemispheric and the interhemispheric coherences of frontal cortex were increased during the decision of MLT accompanied by music. Using of musical accompaniment 85 dB produced a right-side asymmetry in EEG and formed a focus of coherent connections in EEG of temporal area of a right hemisphere.     

The reflection of different levels of the regulation of human brain activity in spectrally coherent EEG parameters]

On the basis of clinico-anatomo-electroencephalographic studies it was shown, that in early terms of cerebral trauma, at gross disturbances of the cortical functions and safety in some cases of only vital regulation, the parameters of the EEG stability or variability are of distinct information value for estimation of the functional state of patients. It was established, that changes of stability of the frequency, power, and coherent EEG characteristics correlate with different parameters of changes of the structural-functional brain organization. At this stage the greatest connection with the disease outcome reveals the EEG coherence parameters of the cortical symmetrical points reflecting the state of predominantly median formations and general brain reactions to traumatic action. In the process of restoration of disturbed neuromental functions priority prognostic significance is acquired by parameters of intrahemispheric coherence as well as by frequency-regional properties of interhemispheric asymmetry of coherence of the brain electrical processes, characterizing functional features of the lesion focus.     

Changes in the functional parameters of the brain structures under the influence of enkephalin-like tetrapeptidamide

In complex neurophysiological and cytobiochemical study single injections of tetrapeptide amide (TPA) caused a short-term analgetic effect which manifested itself in the absence of motor reactions and EEG changes of cortical and subcortical brain structures after painful stimulation of extremities. This effect was accompanied by changes of some indices of transmitter (monoamine oxidase) and protein metabolism in the cerebral hemispheres at cellular and subcellular levels. In 30-40 min after a TPA injection, EEG suppression and absence of EPs to light flashes were observed in cortical and subcortical structures. Simultaneously motor disorders developed. The observed EEG changes had an undulatory character: on the second day EEGs were restored and on the third day--suppressed once again. This period of TPA action was accompanied by varied changes of the investigated types of metabolism. The question of the necessity of systemic approach to the study of TPA action is discussed, as such an approach allows to reveal complex neurophysiological and fine biochemical relations in the reactions of brain structures and in animal behaviour.     

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.     

Spectral analysis of the human EEG in acutely developing foci of irritation at the diencephalic and brain stem levels

The dynamic study of EEG spectra and coherence in 52 patients in early period after tumor ablation at the diencephalic (27 patients) and brainstem (25 patients) levels with favourable (24 patients) and lethal (28 patients) outcomes revealed a dependence of their changes on the reversibility or irreversibility of pathological irritation of these brain levels. At regressively developing foci and retained compensatory mechanisms characteristic changes of EEG relations were seen in the central cortical areas, i. e. in cortical projection zone of the nonspecific thalamic pathways. The changes observed consisted of EEG synchronization in the band of 7 cps and sharp coherence increase while changes of EEG correlations in other cortical areas were unsimilar. Gradual EEG normalization with alpha-rhythm restoration passed through the stage of sigma-rhythm and slow sleeplike waves which indicated the safety of brainstem-subcortical hypnogenic systems. In patients with destructive foci at the diencephalic and brainstem levels, i. e. under conditions of brain functioning similar to "cerveau isolé" and "encephale isolé",--a general coherence decrease and EEG synchronization in the band of 5 cps, or generalized slow, monomorphic oscillations were observed.     

The dynamic characteristics of the interhemispheric correlations of the EEG during the recovery of human neuropsychic activities

In patients (34 right-handed) in remote terms of cerebral trauma (CT) characteristics were studied of interhemispheric EEG correlations depending on lateralization of lesion in comparison with healthy subjects (20 right-handed). Disturbance of neuropsychic activity in patients with CT before treatment was accompanied by changes of interhemispheric asymmetry of conjunction in the form of a decrease of coherence values in the injured hemisphere; the decrease of conjunction values of symmetric cortical zones was determined by laterality of the lesion. After treatment the most effective restoration of neuropsychic activity and of interhemispheric EEG correlations was in patients in whose dynamics of the restoration process the stage of the right hemisphere activation was observed. This stage came earlier and restoration period was shorter in patients with the left hemisphere lesion.     

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.