EEG characteristics determining the quality of subsequent recognition of visual images

Recognition of noisy pictures of Arabic numerals was accompanied by an increase in EEG coherence in the frontal cortical regions, especially in the left hemisphere, and between the frontal and occipital areas in both left and right hemispheres. Coherence values decreased in the temporo-centro-occipital areas of both hemispheres. A correlation was found between the coherence pattern in the prestimulus period and the quality of subsequent activity. Correct recognition was preceded by left-side asymmetry of the EEG coherence. Before erroneous recognition, EEG coherence levels were higher than before a correct response, and the increase in coherence was widely generalized over the cortex (especially in the Δ, ?, and α₁ frequency bands). The frequency of expression of an increased integral EEG coherence was higher before erroneous recognition than before a correct response. These changes in coherence were symmetrical.     

Interactions between electrical activities of the sensomotor cortex and the hippocampus during 'animal hypnosis' in rabbits

The electrical activity of the left and right sensorimotor cortex and left and right dorsal hippocampus (CA3 fields) was recorded during "animal hypnosis" in rabbits. The "animal hypnosis" produced asymmetry in the spectral power of the hippocampal electrical activity due to an increase in the power of delta 1, delta 2, and theta 1 components in the left-hippocampus and decrease in the spectral power in the same ranges in the right-hippocampus. Hemispheric asymmetry in the electrical activity during the "animal hypnosis" was also expressed in the indices of coherence between the sensorimotor cortex and hippocampus. EEG coherence between the left sensorimotor cortex and left hippocampus in the delta 1, theta 1, and theta 2 ranges was higher than that between the right-side structures.     

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.     

Individual resistance to factors of monotony reflected in the EEG

Three groups of operators substantially different in their performance quality were examined. Under conditions of monotonous activity, subjects with the highest initial level of activation, minimum EEG total spectral power, and minimum level of EEG coherence in the frontal cortical areas worked most steadily. Under the same conditions, subjects with a rather high spectral power of the theta and beta2 EEG frequency components, highest coherence in the frontal areas, and low coherence in the caudal areas of the cortex worked least steadily. EEG phenomena testify to a rather low level of activation of the frontal cortical areas associated with a facilitation of cortico-subcortical neuronal interactions and an attenuation of the operating neural streams. This results in a decrease in the level of any attention, its involuntary switching, and short-term loss of the control over the current performance.     

Changes in spectral coherent characteristics of EEG in the early postpartum period in mothers with anxious and depressed mood

Postpartum EEG spectral and coherence characteristics were estimated in mothers with or without postpartum depressions. In mothers without affective disorders the power of oscillations in the delta, theta, and alpha 1 frequency bands was increased as compared to controls. Intrahemispheric EEG coherence between the left frontal and adjacent derivations in the delta and theta bands and interhemispheric coherence in the central areas was increased and decreased over the remaining cortical surface. These changes led to a significant decrease in EEG asymmetry. It is suggested that during normal postpartum the influence of the limbicodiencephalic and lower brainstem structures on the cortex is augmented and a certain kind of dominanta is formed. In mothers with postpartum depressions the EEG alpha-band power was lower than in the control and normal groups, coherence changes in the delta and theta bands diminished the EEG asymmetry. The insufficiency of limbicodiencephalic influence and impairment of adaptive brainstem reactions are suggested to be responsible for problems in the formation of maternal dominanta, which results in the development of postpartum depressions.     

EEG in mathematical logical problem solving

The model of mathematical logic tasks was developed at which decision there was a value coherence in delta-range raised. In low-frequency ranges (delta, theta, and alpha) a coherence of potentials of frontal cortex were increased. In high-frequency ranges (beta1, beta2, gamma) in frontal cortex coherence was decreased, and its increasing in central, parietal, temporal, and occipital areas with prevalence in the left hemisphere. Most changes of quantity of positive connections observed in value diagonal coherence. Analysis of spectral power EEG has shown, that at the decision of tasks there is a generalised raising on a cortex in delta-range. Theta-activity increased in a frontal cortex, and gamma band was raised in occipital areas. A spectral power in an alpha range mainly decreased.     

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 structure of the background EEG of the rabbit in the high-frequency portion of the spectrum]

With the purpose of studying the character and structure of high frequency bioelectric activity of rabbits cerebral cortex in the state of calm alertness, the EEG ensembles of different areas of the cortex (sensorimotor, visual, acoustic) and dorsal hippocampus were studied with FFT method. A supposition was made about the presence of systemic organization of the background EEG in rabbits cerebral cortex, reflected, in particular, in the presence of determined components both of chaotic and rhythmic character having different degrees of manifestation. Heterogeneity was revealed in distribution of energies of spectral EEG components in the studied frequency ranges from 14.7 to 100 Hz with predominance of total specific energy value in the band of 14.7-60 Hz. In coherence functions of all the studied pairs of EEG leads rhythmic component, stable in time, was absent. Functions of the mean EEG coherence in the band of 61-100 Hz had significantly greater values in comparison with the values in the band of 14.7-40 Hz.     

Interhemispheric interactions in right- and left-handed individuals based on EEG coherence data

The functions of interhemispheric EEG coherence were analyzed in 12 healthy subjects with the right individual profile of motor and sensor asymmetry and 7 subjects with the left profile in 2 experimental conditions: the state of rest and photostimulation of the central visual field. It was shown that in the rest condition the right-handed subjects have the higher values of EEG coherence in the thetal band in symmetrical frontal and central areas than the left-handed. These differences decreased for the frontal and central areas during activation caused by photostimulation but increased in the theta 2 and betal bands in symmetrical temporal areas (the coherence in the left-handed being higher). The difference in the EEG coherence between conditions was greater for the frontal and central areas in the right-handed than in the left-handed, especially, for the theta 1 and theta 2 bands. These findings suggest that the left-handed subjects have a less developed hierarchy of subcortical control of the functional state shifts than the right-handed.     

Event-related coherence and event-related desynchronization/synchronization in the 10 Hz and 20 Hz EEG during self-paced movements

To investigate the activity of cortical regions in the control of movement, we studied event-related desynchronization/synchronization (ERD/ERS), event-related coherence (ERC), and phase coherence in 29-channel EEGs from 9 subjects performing self-paced movements of the right index finger. Movement preparation and execution produced ERD over the sensorimotor areas at 10 Hz and 20 Hz, followed by ERS. ERD corresponded spatiotemporally to an increase in coherence over the frontocentral areas. For both frequency bands, ERD began over the left sensorimotor areas and became bilateral at the time of movement onset. The coherence increase with frontal areas began in the left central areas and became symmetrical after EMG onset. The ERD and coherence increase was longer at 10 Hz than at 20 Hz. Phase coherence at 10 Hz showed a lead of anterior regions to posterior regions throughout the time period, and at 20 Hz showed a tendency toward zero phase delay corresponding with the movement. EEG desynchronization parallels functional coupling over sensorimotor and frontal areas. Event-related coherence and phase coherence findings implicate the frontal lobes in control of movement planning and execution. The involvement of different frequency bands with different timings may represent parallel changes in the cortical network.     

Functional coupling of cortical areas during problem-solving task: an analysis of theta rhythm coherence

We analyzed the EEG theta rhythm coherence in adult subjects who performed visual object classification task in the condition of uncertainty. The coherence function was estimated for the EEG segment following a feedback signal. It was shown that the functional coupling of cortical areas was stronger in the process of strategy discovering as comparing to the final period when the strategy is already found. The theta-related functional links are characterized by a specific topographical pattern: they converge to the foci located in the polar frontal cortex and reflect the interaction between the latter and the anterior associative cortices of the left hemisphere and occipital areas of both hemispheres. This pattern of functional connectivity may reflect an interaction between limbic structures and the frontal cortex in the process of strategy formation.     

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.     

A comparison of the spike train activity of the cortical neurons and of the spatial synchronization of the EEG

In chronic experiments EEG coherence and conjugation of impulse activity were compared of neurones of the visual and sensorimotor areas of rabbits neocortex simultaneously recorded with the same electrodes. Connection was revealed between the presence and properties of conjugated neurones activity and EEG coherence at various frequencies. At correlated neurones activity a greater EEG coherence was observed on frequencies of 3-4,5 Hz than at the independent activity. At the highest level of the EEG coherence the neurones discharged with less delay of one after the other in pairs, and in their synchronization a common source participated more often than at the lowest level of the EEG coherence.     

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.     

Spectral correlation analysis of the potentials of the neocortex and certain subcortical structures during low-frequency electrical stimulation of nonspecific thalamic nuclei]

The spectral-correlation analysis of biopotentials in the cortex and some other brain structures (the anteroventral thalamic nucleus, dorsal hippocampus, lateral geniculate body, mid-brain reticular formation), in chronic experiments on alert rabbits, revealed that during electrical stimulation of thalamic mid-line nuclei within the ranges of 1-3, 4-7 and 8-10 c/s, there occured a rearrangement of the EEG frequencies; a dominant, narrow-band peak at the stimulation frequency, appeared. The coherence of the biopotentials of different cortical areas, of the cortex and subcortical formations increased during the stimulation at the frequency of the stimulation, reaching maximum values between the potentials of the visual and sensorimotor cortical areas.     

Characteristics of EEG reactivity changes during the performance of dual tasks in healthy subjects (voluntary postural control and calculation)

Comprehensive EEG and stabilography investigation with separate and simultaneous performance of motor (voluntary postural control) and cognitive (calculation) tasks has been performed in 20 healthy subjects (22 ± 0.7 years). Specific spatial and frequency reactive changes have been found during motor task performance. These included an increase in coherence in the EEG α band for distant derivation pairs in the right hemisphere, as well as in symmetric parietal-occipital areas in both hemispheres. Cognitive task performance was accompanied by an increase in coherence for the slow bands (δ and θ) with a higher activation in the left hemisphere and frontal cortex areas. In performing the dual task, one could observe activation of spatial and frequency changes including both motor and cognitive tasks. In the dual tasks where both components were performed worse as compared to the control, reactive reorganization of EEG coherence was less pronounced than during the performance of separate tasks. A decrease in the coherence of the α₁ band in the frontal areas appeared as a zone of “conflict of interest” or interference. In dual tasks with better performance of each component as compared to the control, EEG coherence increased in each specific area, as well as in the areas of “conflict of interests.”     

Changes in the cortical electric activity in the course of set formation under conditions of increased loading of the working memory

Stability of the cognitive set to nonsense words in healthy adult subjects was compared in two experimental conditions: (1) subjects had only to recognize pseudowords/words; (2) in each trial after the pseudoword/word recognition, subjects had to press a button in response to a visual probe stimulus and only after this action to pronounce a recognized pseudoword/word. It was shown that complication of the cognitive performance in the second condition did not affect the set rigidity. However, the pattern of the cortical electric activity substantially changed: the EEG power in the theta frequency range and coherence function, in particular, interhemispheric, in the frontal cortical areas were higher in the second condition. The increase in coherence function in the frontal areas was most pronounced in the theta and alphal ranges. It was suggested that increase in activity of the frontal regions of the brain cortex facilitates shifts of visual sets under increasing load of the working memory.     

Functional Brain Asymmetry and Individual Differences in Hand Preference in Early Ontogeny

This work was aimed at studying the brain mechanisms of hand preference in 10- to 11-month-old infants. According to the results of neuropsychological investigations, the preference for the right hand in children of this age (at the populational level) primarily arises in actions that demand involvement of the functions of planning and motor control of reaching (functions of the motor control of reaching: FMCR) for an object. The stage of development of the FMCR in each child was scored on the Diamond scale. Total numbers of movements performed by the right and left hands and a coefficient of the manual asymmetry (AC) were calculated. On the basis of quartile analysis of the AC distribution, groups of right-handers, left-handers, and ambidextrals were formed. The EEG was recorded in the state of visual focused attention, and the spectral absolute amplitude density (AAD) of the sensorimotor rhythm and other infant EEG rhythms in the frequency band was analyzed. In order to estimate the statistical correlation of manual asymmetry, gender, and stage of development of the FMCR with functional asymmetry of the AAD of the -band rhythms in different cortical derivations, analysis of variance with factors of repeated measurements and analysis of multiple regression were used. The main results showed that 10- to 11-month-old children with different types of manual asymmetry differed in interhemispheric asymmetry of the visual attention-related EEG -band rhythms (including asymmetry of the sensorimotor rhythm). The maximum differences were observed in the lateral frontal and posterotemporal areas of the brain cortex. The leftward amplitude asymmetry was characteristic of right-handers; in left-handers and ambidextrals, the EEG amplitude was distributed over the brain hemispheres in a more symmetric way. The correlation between the brain and manual asymmetries was stronger in boys than in girls. There was a strict linear correlation between the degree of manual asymmetry and interhemispheric asymmetry of the EEG sensorimotor rhythm in the precentral and lateral frontal brain areas. On the whole, the close correlation of the manual asymmetry with functional asymmetry of the EEG sensorimotor rhythm suggests that it is determined by the formation of the brain FMCR lateralization.     

Relations of the EEG local and spatialtemporal spectral characteristics changes under hypoxia in humans

Spatial temporal and local EEG characteristics were studied in healthy subjects during inhalation of hypoxic oxygen-nitrogen gas mixture with 8 % content of oxygen. Analysis of spectra power density, coherence, phase shift, similarity of dominant frequencies in the EEGs of different derivations was performed separately for the EEG epochs with and without visually detected patterns of spatial synchrony of the EEG. Apart from this, a fact of dominance of the frequency in the EEG spectra of corresponding derivation was taken into account when estimating spectral parameters. Results of the study showed that, in general, under hypoxia, the EEG coherence in alpha- and delta-frequency range decreases as compared to the background level, in beta-range growth of this parameter is observed, in theta-range ambiguous changes occur: in the epochs with patterns of spatial synchrony--growth, in other epochs--lowering. Under hypoxia, also occurs growth of frontal and temporal EEGs' phase shift (corresponding to EEGs other derivations) in delta- and theta-range. In beta-range, on the contrary, average level of the phase shift decreases. It was revealed that taking into account the fact of dominance of frequency in the local EEG spectra is necessary for correct interpretation of the EEG spatial and temporal parameter analysis' results. A mathematical model of interaction between processes with different frequency characteristics is suggested, which explains some facts obtained in the study.     

Interhemispheric relationships of electrical activity in the blinking dominant in rabbits

The study of intercentral and interhemispheric relations of the electrical activity of the cerebral cortex during formation and functioning of winking dominant, by the method of spectral-correlation analysis, has shown that the dominant focus is characterized by an increase of spectrum power in the range of delta-frequencies and a raise of coherence level of potentials in the same range that leads to the appearance of interhemispheric asymmetry according to these parameters. Appearance of the dominant state in the opposite hemisphere is accompanied by a reconstruction of the electrical activity characteristic of dominant focus.