Search

This work was carried out on the model of cognitive set to facial expression under conditions of high load on working memory by lengthening interval between the facial and triggering stimuli to 8 seconds. The aim of this work was to try to reveal, there is the phenomenon of correspondence between the dynamics of gamma- responses (21-60 Hz) to the facial-stimuli and the real "success" of the job (number of mistakes in performing a task): To do this, we used a different method of estimating the power compared to the wavelet transform, as if it is applied in a previous worksuch a dependending was not revealed. In this paper we analyzed the index of the average amplitude, built in a similar method specific variation to estimate the power of gamma responses (range: gamma1-21-40 and gamma2-41-60 -Hz), which revealed correspondence between patterns of gamma responses and the number of subjects admitted mistakes. The obtained results allow us to consider gamma2-responses to facial stimuli as electrographic correlate of states (the so-called their gamma code) corresponding to the adequacy of real actions of the subject at the test under the same conditions of 8-second interval between the facial and trigger stimuli.

The research of changes of a beta rhythm parameters on condition of working memory loading by extension of a interstimuli interval between the target and triggering stimuli to 16 sec is investigated on 70 healthy adults in two series of experiments with set to a facial expression. In the second series at the middle of this interval for strengthening of the load was entered the additional cognitive task in the form of conditioning stimuli like Go/NoGo--circles of blue or green color. Data analysis of the research was carried out by means of continuous wavelet-transformation on the basis of "mather" complex Morlet-wavelet in the range of 1-35 Hz. Beta rhythm power was characterized by the mean level, maxima of wavelet-transformation coefficient (WLC) and latent periods of maxima. Introduction of additional cognitive task to pause between the target and triggering stimuli led to essential increase in absolute values of the mean level of beta rhythm WLC and relative sizes of maxima of beta rhythm WLC. In the series of experiments without conditioning stimulus subjects with large number of mistakes (from 6 to 40), i.e. rigid set, in comparison with subjects with small number of mistakes (to 5), i.e. plastic set, at the forming stage were characterized by higher values of the mean level of beta rhythm WLC. Introduction of the conditioning stimuli led to smoothing of intergroup distinctions throughout the experiment.

Power EEG gamma-band (21-60 Hz) in the process of forming and testing the cognitive set on the face expression is seen in conditions of the model, which provides a higher load on working memory by lengthening the intervals between the target and trigger stimuli to 8 s. The results are compared with data from previous experiments with increased load in the form of additional cognitive tasks, when there was an increase of gamma responses by "success" of the job subjects. In this study, the responses to set-stimuli were observed significant lower (relative to prestimulus period) in all groups of subjects that were treated as inhibition of gamma activity. Significant differences in the levels of power gamma-band between the groups were identified by comparing the set up steps (forming and testing), and frequency-bands. The second important difference is the absence of differences in the dynamics of power patterns gamma2 (41-60 Hz) between groups of subjects depending on the "success" of the job. We present arguments to substantiate the "paradoxical" results in the conditions of use of the plant model.

Beta-rhythm parameters during cognitive set to emotional facial expression were investigate in 35 healthy adults. Formation of the set was supplemented long-time interval (8 c) between a warning and a target stimulus. Rhythmical component of EEG were revealed using wavelet functions. Maximum and mean levels of wavelet coefficient (WLC) in the beta-rhythm were analyzed. We obtained 3 groups of subjects depend on mistakes of recognition facial expression. Group with correct recognition had high WLC mean level during the experiment, WLC maxima during first second of inter-stimulus interval, large latency of WLC maxima during the stage forming and predominance level WLC maxima in the left hemisphere. Two groups of subjects with mistakes in recognition had low WLC mean, maxima and their latency during set forming. Right hemisphere (WLC maxima) dominated in these groups.

Subjects were divided into two equal groups 35 healthy subjects each. Formation of the visual set to facial emotion recognition was supplemented with two types of additional task: either visuospatial (to find a target stimulus among others) or verbal (to tell a word from a pseudoword). The results of the experiments were compared to those obtained in similar experiments without the memory load. Changes in the EEG beta rhythm during visual set forming and testing were studied. The EEG was analyzed by wavelet transformation. Changes in the mean level, maximum and latency of the maximum of wavelet coefficient were rated at different stages of the experiment. All these characteristics for the beta rhythm were higher in experiments with both types of additional memory load as compared to those without the memory load.

The dynamics of power of short-term (0.8 s) induced responses to facial stimuli (wavelet transform in the 15-60 Hz band) were assessed in the study of the visual cognitive set under conditions of different loads on working memory in two groups of subjects. Subjects of the first group had to react only to facial stimuli (n = 29), whereas the second group solved an additional task loading the working memory (they had to find a target stimulus in a matrix of letters, n = 35). We estimated wavelet spectra in the occipital, temporal, central and frontal areas of both hemispheres. In both groups of subjects with the plastic form of set, the power level in the gamma2 band (41-60 Hz) was significantly higher than in subject with the rigid form. In group A at the set-testing stage, the largest increase in the gamma2 band was related to the central areas of the left hemisphere. In more complex situation (group ), the increase in power in the gamma2 and gamma1 (21-40 Hz) bands was observed in the occipital and temporal areas of both hemispheres. At the same time, the EEG power of the central areas in these gamma bands was significantly lower. In the frontal areas there were no significant differences in the dynamics of power between the subjects of both groups.

Power spectra of cortical potentials of baseline activity during interstimuli intervals (4 s; Fourier transform in the frequency band of 1-60 Hz) and short-term (0.8 s) induced responses to facial stimuli (wavelet transform in the 15-60 Hz band) were assessed in the study of the visual cognitive set to facial expression. Significant differences between groups of subjects with different set rigidity were observed only at the set-testing stage. Estimation of the short-term (0.8 s) induced responses of the wavelet spectra in the group with plastic set revealed an increase in the power (in comparison with the power of background activity) of the gamma2 band (41-60 Hz) in the left hemisphere of the temporal, central and occipital areas, whereas in the group with rigid set these power spectra decreased. At the same time the power in the gamma1 band (21-40 Hz) was significantly lower (at the same level with the rigid form), indicating a discrete nature and functional selectivity in the gamma frequency band.

A cognitive set to emotional facial expression was formed in 35 young adults. Rhythmical components of the event-related activity within short time intervals were revealed using wavelet functions. Maximum and mean levels of wavelet coefficient (WLC) were analyzed in the alpha-and theta-bands. In subjects with the rigid cognitive set, the WLC maxima in the alpha-band were higher than that in subjects with the plastic set. The mean level of the theta-oscillations in subjects without set manifestations (plastic set) was higher than in subjects who displayed erroneous responses (rigid set). At different stages of the experiment, different values of the maximum and mean levels were observed in the studied frequency bands. We think that set formation (and extinction) is associated in different groups of subjects with different cortico-subcortical relations at different stages of the set.

Interhemispheric relations of the EEG power in the 1-60 frequency band were studied at the stages of formation and testing of the cognitive set to facial expression. Different topographic asymmetry patterns were revealed in subjects with different set plasticity. In subjects without behavioral actualization (n = 11) of the set at the stage of set formation, EEG power in the gamma band (21-40 and 41-60 Hz) prevailed in the frontal areas of the right hemisphere, whereas the power of electrical oscillations in the bands of 2-7 and 8-13 Hz was higher also in the frontal areas but of the left hemisphere. At the stage of set testing, this basic topographical asymmetry pattern persisted. Formation of the set in subjects with pronounced actualization (n = 18) was characterized by another topographical asymmetry pattern: a significant excess of the power of gamma oscillations was observed in the posterotemporal and occipital areas of the left hemisphere, whereas the power of oscillations in the bands 2-7, 8-13, and 14-20 Hz was higher also in the posterior areas but of the right hemisphere. No asymmetry in the EEG power was observed in these subjects at the stage of set testing.

Power spectra of cortical potentials in the frequency band of 1-60 Hz were estimated in 29 healthy subjects in the states of rest with the open eyes, after listening to instruction, and in prestimulus periods at the stages of forming and testing of the visual cognitive set to facial expression. Comparative assessment of the power spectra in five frequency bands 2-7, 8-13, 14-20, 21-40 and 41-60 Hz revealed a significant decrease in the power for the frequencies of 1-20 Hz and its parallel increase in the band of 21-60 Hz in all the states under study as compared to the state of rest. At all the set stages, interregional differences in the EEG power were the highest in the bands of 1-20 and 41-60 Hz and the lowest in the band of 14-20 Hz. Significant differences between the "plastic" and "rigid" groups in the power dynamics were observed only at the set-testing stage. Thus, in subjects with the plastic set, the power of the gamma-frequency band was more frequently higher than in subjects with the rigid set.

Theoretical analysis of variational characteristics was performed and their practical validity was proved as applied to electroencephalogram. These characteristics are remarkable for both simplicity of computer calculation and the fact that they reflect the most essential features of an EEG curve with a highest possible compression.

Alpha- and theta-band EEG synchronization/desynchronization, induced by the presentation of emotionally negative stimulus (angry faces), was studied in 35 healthy adults. In subjects with a plastic set induced theta-synchronization was greater, and its latency was shorter, than in subjects with a rigid set. This difference is particularly apparent in temporal and parieto-occipital brain regions. A sufficiently high level of theta-synchronization is essential for a quick set-shifting. This synchronization reflects the activity of cortico-hippocampal feedback system and its participation in the perception of emotional faces. In subjects with a plastic set this process induces alpha-synchronization, and in subjects with a rigid set--desynchronization. W. Klimesh (2007) suggests, that induced alpha-synchronization reflects processes of inhibition in cognitive activity. This inhibition plays an important role in the set-shifting. The role of tonic and phasic forms of cortex activation, produced by cortico-hippocampal and fronto-thalamic systems, in the shifting of a cognitive set to facial face expression is discussed.

Prestimulus EEG power spectra from different cortical areas in frequency band 1-60 Hz were studied at a stage of formation of the cognitive set to facial expression. Diversity of individual power spectra of baseline EEGs, especially in gamma frequency band 41-60 Hz makes averaging individual spectra impossible. The authors pioneered in finding that, in prestimulus periods, EEG frequencies 41-60 Hz were of higher information value than frequencies 1-20 and 21-40 Hz. The highest power of the gamma frequencies was revealed in the frontal areas of the right hemisphere in subjects with a plastic set. In the group with a rigid set, gamma frequencies of high power prevailed in the posterotemporal and occipital areas of the left hemisphere.

Power spectra of short-term (less than 1 s) EEG-reactions (in the frequency band of 1-225 Hz) were studied in dogs in the course of instrumental food conditioning. These reactions were observed in different areas of the cortex in response to positive and differentiated conditioned stimuli. Regional features between the spectra were found both in the power level and frequency structure. The power of the reactions in the visual and parietal areas of the left hemisphere was higher than in the motor areas. Power spectra of reactions to differentiated stimuli were significantly lower than the spectra of reactions to positive stimuli mainly owing to the high-frequency components (80-225 Hz). In these both cases, prestimulus power spectra did not differ. The frequency structure of corresponding EEG-reactions consisted of individual spectral peaks, mainly both gamma (30-80 Hz) and higher-frequency (80-225 Hz) bands.

Energy characteristics (power spectra) of short-term (less than 1 s) EEG-reactions were studied in dogs in the course of instrumental conditioning. These reactions were observed in different areas of the cortex during selective attention in response to positive conditioned stimuli. They immediately preceded strong blow with a paw on the pedal of feeding cup and taking the reward. The EEG power at these moments was 1.5-3 times higher than the baseline EEG power level in a prestimulus period. The high-frequency structure of corresponding EEG reactions comprised discrete individual spectral peaks both in traditional (1-30 Hz) and gamma (30-80 Hz) ranges and higher-frequency components (80-200 Hz) as well. In some cases, the higher-frequency components (80-200 Hz) were most pronounced.

Coherent-phase characteristics of cortical potentials (1-220 Hz) derived from different cortical point of both brain hemispheres of dogs were analyzed in the state of selective attention developed in the course of instrumental food conditioning. Among the compared cortical points, functional groups were found that were probably of priority for the state of selective attention. Values of coherence function between these derivations (an assessment of temporal relations) were at a certain optimal level (about 0.7), predominantly, in the frequency ranges of 1-15 and 40-200 Hz. Under such conditions, if the average phase shifts between the potentials were near zero, phenomenon of potential synchronism was formed. In case of significant phase shifts, phenomenon of asynchronous temporal relations with a certain spatial direction developed.

The state of selective attention was studied in dogs in the course of instrumental conditioning. During interstimuli intervals, this state was manifested in the state of strained waiting for conditioned stimuli. Electrical activity of different areas in both hemispheres was analyzed using the Fast Fourier Transformation. It was shown that in the process of development of selective attention, the high-frequency EEG components (40-200 Hz) in the motor area of the right hemisphere and the visual and parietal areas of the left hemisphere had a predominant significance over the traditional EEG frequencies of 1-30 Hz. The state of selective attention was characterized by another functional mosaic organization of the neocortical potentials.

The study was aimed to reveal the subbands of correlated changes in power spectral density of brain electrical activity (EA), including the low-voltage (up to 10 microV) high-frequency (HF) components (40-200 Hz) in dogs during instrumental conditioning by means of factor analysis. The values of the EA spectral density in interstimulus intervals calculated with a resolution of 1 Hz were used for subsequent factor analysis (the standard principle component technique with varimax rotation). Twenty factors could explain about 80% of total variance. The groups of frequencies which were presented by comparatively narrow peaks (2-3 points) of high loads (more than 0.6) of single factors ("stable" factors) were taken into consideration. In the process of conditioning the factor organization of the EA became substantially complicated, the number of the "stable" factors increased. It was originally shown that the high loads of these factors divided the HF band in comparatively narrow frequency subbands, which appear to reflect the functional mosaics in the neocortex.

A notion is introduced about the brain processor as a natural mechanism of brain activity, which is close to the neurocomputer technology. In contrast to the common computer metaphor, this notion can be used as a real basis for explanation of many brain phenomena.

The EEG phenomenon was studied of high-frequency bursts (60-70 Hz, 70-80 mcV) in electrical activity of dog's neocortex (EA, 1-200 Hz) in the process of instrumental conditioning. These bursts of high-frequency oscillations appeared at the generalization state of the conditioned reflex during interstimulus intervals at the background of dominant EA of the lower frequency and voltage (10-40 mcV). Application of the developed by us novel strategy of the primary analysis of EA realizations (in particular, inhomogeneity coefficient) enabled estimation of the amplitude-frequency EA inhomogeneity, namely, high-frequency bursts. The regional peculiarities of the high-frequency bursts were revealed by means of the original technique based on the expansion of EA oscillation into a system of half-waves and construction of distribution maps on the basis of their parameters. The presented data verified our earlier findings obtained using other techniques (FFT analysis and factor analysis). These data testify to differential participation of cortical areas (even those which are close to each other within a distance of 3-5 mm) in the spatio-temporal organization of potentials characteristic for a given learning paradigm.

The qualitative techniques are considered of mathematical description of curve inhomogeneity which adequately reveal non-stationary fragments in EEG samples with a pseudorandom process. The introduced inhomogeneity coefficient turned to be a sufficiently adequate indicator of the presence of short-term high-frequency bursts in the electrical activity of dog's brain and a sensitive index for discrimination of quasihomogeneous fragments by the level of "general activation". It is shown that the values of this coefficient reflect the individual features of the brain electrical activity of the animals and its dynamics in the process of alimentary motor conditioning. At the same time, this index is ineffective in revealing the regional differences. A novel approach is developed for signal inhomogeneity description which is based on the traditional harmonic analysis (Fourier transform).

The study was aimed to reveal frequency ranges of correlated changes of power spectral densities of the brain electrical activity (EA) including the high-frequency components (HFC) in dogs (4 animals) by means of factor analysis technique. Spectral densities of EA in different cortical areas and olfactory bulb were factored. Relationships between the structure of the selected factors both by the parts of the total variance determined by them and their frequency loads suggest the regional and individual EA differences. In the process of learning (elaboration of motor skill of pressing the food-dispenser pedal with a forepaw) the factor organization of the EA became substantially more complicated, mainly, in the HFC-range (40-170 Hz). This was manifested in formation of narrower frequency subbands of the HFC each of which being highly loaded (0.7-0.8) by one of the factors. The evidence obtained by means of the FA was completely verified using original version of cluster analysis.

The work was aimed to reveal the functional significance of separate narrow-frequency bands in the high-frequency range (40-200 Hz) of brain electrical activity of dogs in the process of lever-pressing instrumental conditioning. In order to divide this range into separate bands we applied one of the methods of multivariate statistics, factor analysis (FA) with varimax rotation. Values of function of spectral density in the wide range (1-200 Hz) were factorized. The structure of factors reflected both regional cortical characteristics of electrical activity and individual features. Conditioning induced changes in factor description of brain electrical activity mainly in the high-frequency part of the spectra. A number of new factors appeared which divided high-frequency band of the brain activity into narrower parts with definite functional significance.

EEG reactions to positive and differentiated signals were compared during lever-pressing alimentary conditioning in dogs by means of described by us earlier non-standard forms of EEG analysis in a wide frequency band (1-256 Hz). Findings concerning EEG reactions to positive stimuli, confirmed the earlier obtained data on a high representativeness of the high-frequency components of dog's EEG. EEG reactions to differentiated stimuli were also excitatory. Developed by us techniques allowed us to show some quantitative characteristics of these reactions. Diversity of expression of high-frequency components in different dogs, accompanied by similarity of their effector reactions (absence of movement), was considered as a reflection of individual features of their CNS.

A new method of EEG coding (alternative to classical FFT) was worked up. It allowed to compensate for limitations of FFT and to obtain new information on the shape of EEG curve reflecting peculiarities of oscillations of potentials. Proposed technique of EEG coding seems to be adequate for revealing individual and regional features of EEG and their estimation at different stages of instrumental conditioning. Data obtained using this method confirm the reality of high frequency EEG components of small power. In addition, by the method used the intensification of slow wave EEG components was demonstrated in some cortical regions which could not be revealed by FFT.

Background electric activity was studied of different neocortex areas in interstimulus intervals at the stage of generalization during elaboration of motor alimentary conditioned reflexes in dogs. For this stage the appearance is typical of short-term (0.1-0.3 s) packs of high frequencies (above 40 osc./s) significantly exceeding the adjacent initial background by frequency and amplitude (along side with motor interstimulus reactions). The index of specific variation, elaborated by us, allowed to single out this EEG pattern in the initial realizations of the background activity during their input in the computer. With the purpose of further evaluation of the above phenomenon parameters non-standard approaches of computer analyses were used, directed to decomposition of the EEG curve into the system of oscillations and receipt of corresponding amplitudes frequencies distributions (maps). It was shown, the described high frequencies packs were localized on these maps in definite sufficiently compact places.

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.

With the purpose of levelling the restrictions appearing at the EEG correlative-spectral analysis, particularly of short (1-2 sec) realizations, as a result of Fourier transform, a new algorithm is elaborated of decomposition and analysis of bioelectrical activity. The created algorithm of complete EEG reduction to the list of oscillations singled out has been tested by a corresponding program. It provides for the measurement of parameters of concrete characteristics of the curve, and the adequacy of decomposition is ascertained by the exact restoration from the list of oscillations of the initial EEG. The method shows good sensitivity to the revealing of transient EEG phenomena and also regional specificity of the cortical bioelectrical activity.

The work is a logical continuation of previous studies (analysis of the background electrical activity in the band 1-100 Hz in interstimulus intervals in the process of lever pressing alimentary conditioning in dogs) and it is dedicated to correlation-spectral analysis of prestimulus periods and EEG-reactions to conditioned stimuli, previous to conditioned lever pressing. Visually the EEG reactions present discharges of high-frequency (40-100 Hz) synchronized activity preceding for 40-300 ms the beginning of the changes in EMG of the "working" limb. It is shown that EEG reactions are characterized (in comparison with the background activity) by a higher energetic level and a greater expression of the high coherence (I greater than 0.75) and also by greater phase shifts, in counterbalance to the domination of little phase shifts in the background activity. It is assumed that the patterns of EEG reactions may participate in trigger mechanisms either eliciting conditioned motor reactions (to positive conditioned stimuli) or preventing them (to inhibitory conditioned stimuli).

Phase-coherent characteristics of neocortex background electrical activity were studied in a wide frequency range (1-100 Hz) during interstimulus periods in the process of elaboration of motor alimentary conditioned reflexes in dogs. It was shown that the process of learning led to a considerable increase of the part of high (greater than 0.75) and significant (0.5-0.75) coherences, and also of small (0 +/- 15 degrees) and accounted (+/- 16 - +/- 30 degrees) phasic shifts as compared with the state of calm wakefulness. This increase lay mainly in the high-frequency range (40-100 Hz). The analysis of the interregional relations showed that they differed not only by values of phase-coherent characteristics, but also by distributions of the latter. The obtained data testify that the state of activation is manifested both in the rise of frequency of potentials oscillations and in the increase of their synchronization.

The spectra of coherence (Coh) and phasic shifts (PhS) of cortical potentials were studied by correlation-spectral analysis in a wide frequency range (1--100 Hz) in dogs in a state of quiet wakefulness. Estimation was made by parameters: significant Coh (above 0.5), high Coh (above 0.75), considered PhS (not above +/- 30 degrees), small PhS (not above +/- 15 degrees C). The presence is shown of individual features in coherent-phasic characteristics of neocortex potentials. High values of cross-correlation coefficients (Cc) between cortical potentials correspond in Coh spectra to a great part (90--100% peaks) of significant Coh, in which the great part (90--70% peaks) belongs to the high Coh with small PhS (in most cases). A certain correspondence, though expressed weaker, persisted also for lower values of Cc, Coh, and considered PhS. Coherent-phasic relations between potentials of certain cortical areas are characterized by stability in each animal; a tendency to it is manifest in all animals, despite individual differences of the brain electrical activity.