EEG dynamics during conditioning in symmetrical neocortical regions in dogs

Changes in the frequency of the EEG recorded in symmetrical areas of the frontal and auditory cortices were studied during food conditioning in four dogs. Spectral-correlation analysis was applied. EEG frequency changes depended on individual features of the animals, frequency band, and stage of conditioning. In the beta-2-range, the EEG frequency increased in comparison to the initial values in all the dogs. In three dogs, the EEG frequency in the beta range decreased in the frontal and increased in the auditory cortex. Heterodirectional frequency changes led to the development of the functional interhemispheric EEG asymmetry that was partial and dynamic. At the initial stages of conditioning higher activity was in the left hemisphere, later on asymmetry was absent (or activity of the right hemisphere predominated).     

Functional asymmetry of the neocortex electrical activity during food conditioning in dogs

Four dogs were trained to perform a conditioned alimentary response to a sound stimulus. The EEG was recorded from six pairs of chronically implanted neocortical electrodes. The EEG spectra and coherence functions between the neighboring derivations of each of the hemispheres were analyzed in the theta, alpha, beta 1 and beta 2 frequency ranges. At the first stages of conditioning, the percent of cases increased when the highest mean values of EEG frequency were localized in the left hemisphere. Later on the percent of cases, when the mean coherence values in the left hemisphere were higher than in the right hemisphere, also increased. At the stage of conditioned response stabilization, this asymmetry either disappeared or the right hemisphere became more active than the left one. The spatial localization of the maximal values of the EEG frequency was different for different frequency ranges. The highest values in the beta 1 range were more frequently registered in the posterior cortical regions and in the beta 2 range they were revealed, predominantly, in the anterior areas. The maximal values of coherence dominated in the anterior regions and their spatial distribution was similar for different frequencies. Thus, the initial stages of conditioning are accompanied by activation of the left hemisphere.     

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.     

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.     

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.     

Characteristics of disturbances of intercortical and cortical-subcortical integration in various clinical forms of neurotic depression

Cross-correlation, coherent, and factor analyses of the EEG were used to detect disturbances of spatial organization of brain bioelectric activity, with certain specific features determined by concomitant anxiety and asthenia syndromes in 20 patients with various clinical forms of neurotic depression. In the group of patients with dominance of the depressive syndrome without marked symptoms of asthenia or anxiety, opposite changes in the anterior areas of the right and left hemispheres were found; the interregional relationships of the EEG of anterior areas of the right hemisphere were decreased as compared to the norm, while the normal level of systemic interaction of bioelectric potentials of the cortex of the left hemisphere was increased. In patients with the depressive syndrome combined with increased anxiety, as well as in patients with distinct asthenic symptoms, a considerable decrease in the level of interregional interactions of bioelectric potentials in frontal regions of the cortex of both hemispheres was detected. This was accompanied by an increase, as compared to the norm, of the level of distant relationships of the EEG in posterotemporal, parietal, and occipital regions. The data indicate that, in the case of neurotic depression, irrespective of concomitant anxiety and asthenia syndromes, there is transient inhibition of the functional activity of frontal regions along with an increased rigidity of systemic interactions of the posterior regions of the cortex of both hemispheres. This suggests that neurotic depression is accompanied by dysfunction of intercortical and cortical-subcortical integration, which causes a disturbance of the systemic organization of ordered interactions of the activity of the anterior and posterior regions of both hemispheres, with certain specific features in patients of each group.     

Characteristics of the interhemispheric EEG relationships in assessing the functional state of the human brain

In healthy subjects (11 right-handed men) reorganization was studied of intra- and interhemispheric correlation of the electrical brain activity at transition from the state of alertness to drowsiness. At the lowering of alertness level, the coherence of hemispheres symmetrical points changed not abruptly, with a tendency towards an increase at differently directed character of changes of combinations of separate physiological rhythms ranges. Comparison of the EEG coherence changes within the right and left hemispheres revealed a greater reactivity of the left (dominant) hemisphere. The reduction of the predominance (observed in the dominant hemisphere in alertness) of the degree of EEG conjunction, at transition to drowsiness, leads to smoothing of interhemispheric asymmetry in the organization of electrical brain processes.     

Features of cerebral support of verbal processes in children with dysgraphia and dyslexia

Comprehensive neuropsychological and electroencephalographic examination of children with dysgraphia and dyslexia demonstrated local EEG anomalies in various zones of the cortex in both hemispheres, mainly in the posterotemporal and/or anterior regions of the left and the posterotemporal regions of the right hemisphere. The character of speech disturbances depended considerably on the localization of the baseline EEG anomalies: disturbances of motor components of writing prevailed when these anomalies were localized in the anterior parts of the left hemisphere, while phonological and morphological speech disturbances were noted in children with local anomalies in the temporal regions of both hemispheres and in posterior association regions, mainly in the right hemisphere. Spectral and correlation analyses of the EEG demonstrated the features of the cerebral organization of verbal activity in children with dysgraphia and dyslexia, namely, weakened intra- and interhemispheric integration of electrical activity of different regions of the brain cortex, particularly temporal and posterior association regions, and predominance of integration based on low-frequency EEG components ( and ₁), unlike children without learning disabilities, in whom functional integration of cortical zones involved high-frequency rhythms (₂ and ). On the whole, the results of the study testify to an important role of systemic interactions between the regions of the cortex of both hemispheres in the formation of verbal activity.Translated from Fiziologiya Cheloveka, Vol. 31, No. 2, 2005, pp. 5–12.Original Russian Text Copyright © 2005 by Dmitrova, Dubrovinskaya, Lukashevich, Machinskaya, Shklovskii.     

EEG study of the anxiolytic effect of scopolamine

Effect of the central M-cholinolytic scopolamine on spatial organization of the rat brain electrical activity was studied under conditions of high and low emotional-stress responses. The EEG changes were estimated by 840 parameters. A possibility of the EEG discrimination by means of interstrain differences in responses to scopolamine, was shown. A more obvious decrease in spectral power and potentials coherence was revealed in Maudsley Reactive rats (MR) as compared with the Maudsley Nonreactive rats (MNRA), in parieto-temporal and occipital areas of the right hemisphere, and the reverse interrelationship occurred in the anterior parts of the right and posterior parts of the left hemisphere. These findings suggest some specifics in the spatial distribution of the maximum scopolamine action foci depending on the initial emotional level. Changes occurring under the scopolamine effect in different EEG frequency bands are different in the MR and the MNRA rats. The findings are discussed in respect to the EEG indices of anxiolytic component of cholinergic regulation of the brain activity.     

Systemic Interaction of the Cortical Areas during Performance of Verbal–Mnestic Activity

The dynamics of the interregional interaction of cortical areas was studied in adult test subjects who accomplished the tasks of listening to and memorizing a poem and of mental arithmetic. Analysis of the spatial and temporal relations of the oscillations of the brain biopotentials showed the participation of many regions of the left and right hemispheres in the verbal–mnestic activity. The interaction was most expressed between the posterior regions of the left hemisphere and the anterior regions of the right one. To find out whether these data agree with the classical concepts on the leading role of the left hemisphere in speech activity, the authors examined 3- and 4-year-old children with motor alalia. A comparison of 3-year-old alalics with the control group of healthy children of the same age demonstrated a marked weakening of the distant interaction of the activity of the ipsilateral antero- and posterotemporal regions of the left hemisphere (i.e., those that correspond to the Broca area and Wernicke zone) both between themselves and with the activity of other cortical regions of both hemispheres. These results confirm the important role of both the inter- and intrahemispheric relations, especially those between the Broca area and the Wernicke zone, in realizing verbal–mnestic functions. A significant weakening of the systemic interaction between EEG oscillations in these areas in alalic children suggests that the auditory feedback plays a special role during speech production in the ontogenetic development of the neurophysiological mechanisms that are responsible for speech function formation.     

Interhemispheric motor asymmetry of conditioned feedback

The interhemispheric asymmetry and lateralization of motor functions, as applied to backward conditioning, was studied in two dogs that afterwards turned to be a right-hander and a left-hander. In the process of food-procuring instrumental conditioning it was revealed that one of the dogs predominantly used the right paw (with the dominance of the left hemisphere) and the second animal used the left paw (the right brain hemisphere dominated). The earliest signs of lateralization of the motor functions were observed in the backward conditioned connections (which had been formed earlier than the direct connections or direct conditioned reflexes). Consequently, the presence and sign of asymmetry can be predicted on the basis of manifestation of the backward connections observed at the early stages of acquisition of food-procuring behavior. The backward connections are strictly specific and have the same lateralization as the direct ones.     

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.     

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.     

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.     

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.     

The asymmetry of cerebral hemispheric activity in dogs in a state of quiet wakefulness under the action of sensory stimuli and food deprivation]

The EEG was recorded in four dogs from symmetrical cortical areas of the left and right brain hemispheres. Activation foci were determined by the maximal values of the mean frequency of EEG oscillations and coherence function. In the background experiments, the hemispheric activation asymmetry was observed in all dogs. The individual differences were in the frequency ranges, which were asymmetrically localized. In three dogs the coherence level was significantly more frequently higher in the right hemisphere than in the left one, in one dog the opposite relations were observed. These differences in activation foci localization were correlated with different tactics of choice between two feeders under conditions of free behavior. Under the action of external stimuli, changes in hemispheric activation were observed, predominantly, in the corresponding projection areas, and at the shifts of food excitability they were localized in symmetrical frontal areas. The results suggest that the left hemisphere becomes more activated during the first presentations of indifferent stimuli, i.e., during the development of the reaction to novelty, and under conditions of food deprivation, which rises the level of brain activation.     

Role of the Right- and Left-Hemispheric Structures in Speech and Memory Formation in Children

The role of structures of the left and right cerebral hemispheres in formation of speech function and memory was studied on the basis of complex examination of children with developmental speech disorders. On the basis of EEG estimation of the functional state of the brain, children were classified in two groups depending on the side of localization of changes in electrical activity: those with local changes in electrical activity in the left hemisphere (group I) and those with changes in the right hemisphere (group II). The medical history suggested that the observed features of topography of local changes in electrical activity were linked with the character of prenatal and labor complications and their consequences leading to embryo- and ontogenetic disorders in development of different brain regions. Comparison of the results of neuropsychological examination of the two groups showed that different regions of the brain cortex of both the left and right hemispheres are involved in speech formation. However, a specific role of the right hemisphere in formation and actualization of automatic speech series was revealed. It was suggested that the integrity of gnostic functions of the right hemisphere and, primarily, the spatial organization of perception and movements is a necessary factor of development of auditory–speech and nominative memory.     

Sex differences of spatial-temporal organization of biopotentials of the brain in adults and child 5-6 years old

Research of topical features of spatial structure of EEG distant relationships has been performed with correlation and coherent analyses of EEG for 26 children of 5-6 years old (12 boys and 14 girls) in comparison to the data at 33 adult subjects (15 men and 18 women). Men have much higher level of EEG intrahemispherical relations of posttemporal and frontal regions of the left hemisphere whereas women have the higher level prevalence of interhemispheric interactions, especially of bilateral-symmetrical arials of both hemispheres. Preschoolers have another character of sex differences in the system organization of inter-regional interactions of brain biopotentials than adults. In particularly the girls have exceeding of EEG distant relations in the same zones of left hemispheres, where at men such relations have exceeding in comparison with woman. The obtained data shows that the pronounced sexual dimorphism of inter-regional interactions of cortical biopotentials at adults and at children is formed, first of all, owing to of EEG distant relations topology differing in males and females subject. Investigation sex differences of spatial-temporal organization of biopotentials of the brain in children can promote forming of more hole and deep understanding of role of sex factor in development of human brain system activity.     

Individual typological characteristics of higher nervous performance and asymmetry of hippocampus and amygdala electrical activity in dogs

Electrical activity of the frontal cortex, dorsal hippocampus, basolateral amygdala and lateral hypothalamus of both hemispheres was recorded in nine dogs in the state of quiet wakefulness without any stimulation. Individual typological features of higher nervous activity were assessed by the animal performance under conditions of free choice of the reinforcement mode: either high probable but of low alimentary quality, or with low probability but more valuable. Mean values of the maxima of crosscorrelation function between electrical activity of the investigated structures of two hemispheres were used as a basis for assessment of conditions for interaction between left and right formations. For the hippocampus and amygdala, in some dogs these conditions were the best in the theta and beta 2 ranges, in other animals--in the theta and alpha bands. In phlegmatic dogs, spectral densities in the theta range were higher in the left hippocampus than in the symmetrical structure, in sanguine animals spectral densities in the theta and beta 2 ranges in the hippocampus and amygdala were higher in the right hemisphere than in the left one. Thus, the hemispheric asymmetry of electrical activity of the limbic formations seems to be an important factor, which determines the individual typological features of the higher nervous activity in dogs.     

Neuropsychophysiological correlates of reactive depression

To justify neurophysiological correlates of depressive disorders, the spetral parameters of EEG, peak latencies of the “late” components of auditory cognitive evoked potentials, and latencies of sensorimotor reactions in middle age and elderly patients (aged 53–72 years) during therapy of prolonged psychogenic depressive reaction (F43.21 according to ICD-10) have been studied. Initial depression severity was associated to the EEG signs of decreased functional state of the anterior areas of the left hemisphere and increased activation of the right hemisphere (especially, its temporal areas). Pronounced improvement of clinical state under the affect of psychopharmacotherapy was accompanied by acceleration of the sensorimotor reactions, a decrease in peak latencies of the “late” components (P2, N2, and P3) of auditory cognitive evoked potentials and associated with the EEG signs of improvement of functional state of the posterior areas of the brain, an enforcement of inhibitory processes in the right hemisphere (especially, in its frontal, central, and temporal areas) and more pronounced activation of frontal areas of the left hemisphere. The data are in good agreement with the concept on the systemic character of impairments of brain functioning in depression, as well as on the preferential role of the left hemisphere in control of positive emotions and the right one, of negative emotions.