[Dynamics of the Gamma-Responses Power at 8-second Interval between Facial and Trigger Stimuli Depending on the Success of the Job.]

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.

[Influence Additional Cognitive Tasks on EEG Beta Rhythm Parameters during Forming and Testing Set to Perception of the Facial Expression].

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 of gamma responses to facial expression at eight second interval between the target and trigger stimuli].

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 changes during cognitive set to emotional facial expression with supplemented long-time interval between a warning and a target stimulus].

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.

[Additional memory load causes changes in induced EEG beta-rhythm in experiments with a visual set formed to facial expression].

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.

[Dynamics of the gamma-band power of induced EEG responses to facial stimuli with increased visual working 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.

[Baseline gamma activity EEG and induced responses to facial stimuli of the visual cognitive set].

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.

[Wavelet transformation of event-related cortical activity during formation of visual set to emotional face image].

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.

Dynamics of EEG power spectra at 1-60 Hz during the prestimulus periods at different stages of a cognitive set to a facial expression.

Power spectra of cortical potentials at frequencies of 1-60 Hz were assessed in subjects in the state of resting with the eyes open, after listening to instructions, and during the prestimulus periods at the stages of forming and testing a cognitive set to a facial expression. Comparative assessment of power spectra in five frequency ranges (2-7, 8-13, 14-20, 21-40, and 41-60 Hz) showed significant decreases in the power of potentials in the 1-20 Hz frequency band in most subjects, along with a parallel increase in power in the 21-60 Hz band in all states, as compared with the resting state. Interregional differences in power were maximal in the 2-7 and 41-60 Hz bands and minimal in the 14-20 Hz band. In terms of power dynamics in the states being compared, intergroup differences were seen only at the test stage. Thus, a larger proportion of subjects with the plastic type of set had greater power in the gamma frequency range than was the case in subjects with the rigid type of set.

Evoked synchronization/desynchronization of cortical electrical activity in response to facial stimuli during formation of a set to an emotionally negative expression.

Evoked EEG theta and alpha rhythm synchronization/desynchronization responses to facial stimuli were studied in healthy subjects (n = 35) in an experiment involving formation of a set to an emotionally negative facial expression. The magnitude of the evoked theta activity synchronization response in the group of subjects with the plastic type of set was greater and the latent period was shorter than in the group with the rigid type of set. These differences were particularly clear in the temporal and parietal-occipital areas. A sufficiently high level of the phasic theta potentials synchronization response, reflecting the level of activity of the corticohippocampal feedback system during the perception of facial stimuli, was required for rapid substitution of the set to facial expressions. In subjects with plastic sets, the evoked low-frequency alpha potentials response was apparent as synchronization, while that in subjects of the "rigid" group consisted of desynchronization. These results were interpreted in terms of the concept of Klimesch (2007) that the evoked alpha potentials synchronization response is a measure of inhibition in cognitive activity. The alpha potentials synchronization response reflects the process of inhibitory control, which plays an important coordinating role in organizing the plastic properties of the set in relation to its inhibition when it ceases to correspond to new stimuli. The involvement of the tonic and phasic forms of cortical activation, mediated by the corticohippocampal and frontothalamic brain systems, in the functional organization of the cognitive set to an emotionally negative facial expression is discussed.

[Interhemispheric relations of the EEG power of cortical potentials in the band of 1-60 Hz during formation and testing of cognitive set to facial expression].

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.

[Dynamics of the EEG spectral power in the frequency band of 1-60 Hz in prestimulus periods at different stages of the cognitive set to facial expression].

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.

[Estimation of the validity of variational characteristics of pre- and poststimulus EEG by the chi-square test].

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.

[Event-related synchronization/desynchronization of cortical theta- and alpha-electrical activity and cognitive set to emotionally negative face expression].

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 gamma frequencies during formation of a cognitive set to facial expressions.

The power spectra of baseline (prestimulus) EEG recordings from various parts of the cortex in the band 1-60 Hz were studied in adult subjects during the stage of formation of a cognitive set to facial expressions. Individual variability in the power spectra of the baseline EEG, particularly in the gamma range (41-60 Hz) made it impossible to average spectra from different subjects. This is the first study demonstrating that the EEG at 41-60 Hz was more informative during the prestimulus period than recordings at 1-20 Hz and 21-40 Hz. High levels of gamma-frequency power were found to be dominant in the frontal areas of the right hemisphere in groups of subjects with plastic sets; the group of subjects with a rigid set showed dominance of gamma-frequency power in the posterior temporal and occipital areas of the left hemisphere.

[Prestimulus EEG gamma frequencies during formation of a cognitive set to facial expression].

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.

Regional characteristics of electrical responses (in the band 1-225 Hz) in the cerebral cortex to conditioned stimuli in operant conditioning.

Power spectra of short-term (less than 1 sec) electrical responses to conditioned stimuli were studied over the frequency range 1-225 Hz in dogs during food-related operant conditioning. These spectra demonstrated regional characteristics in terms of energy levels and frequency composition. Responses were more marked in the visual and parietal areas of the left hemisphere. Power in responses to a differential stimulus were significantly lower than with responses to positive stimuli, mainly because of the high-frequency range (80-225 Hz); energy levels in these two situations were similar during prestimulus intervals. The frequency composition of responses was defined by a series of discrete frequencies in the gamma (30-80 Hz) and high-frequency ranges.

Electrographic correlates of adequate and erroneous responses evoked by conditioned signals of different functional signs during operant learning in dogs.

Power spectra over the frequency range 1-225 Hz in short-term (less than 1 sec) EEG reactions arising in different areas of the cerebral cortex in response to presentation of differential signals were investigated in dogs during operant feeding behavior in conditions of both adequate and erroneous responses. The energy levels of these reactions decreased several-fold as compared with responses to positive signals, mainly because of frequencies in the high-frequency range (90-225 Hz), where power was greater than not only the traditional range of 1-30 Hz, but also the gamma range of 30-80 Hz. The frequency composition of EEG reactions in adequate responses was determined by a series of discrete frequency subgroups belonging predominantly to the high-frequency band. In erroneous reactions, the discrete structure of the corresponding EEG reactions was lost.

[Regional features of electrical reactions (in the frequency band of 1-225 Hz) in the cerebral cortex to conditioned stimuli in the course of instrumental conditioning].

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.

Electrographic correlates of "internal states" evoked by positive conditioned stimuli during operant training in dogs.

Experiments were performed to address the energy characteristics (power spectra) of short-term (less than 1 sec) EEG reactions arising in different areas of the neocortex in response to positive conditioned stimuli presented in conditions of selective attention. These EEG reactions directly preceded the motor reactions, which consisted of a strong blow with the paw on a feeder pedal to obtain reinforcement. The energy levels of EEG reactions were 1.5-3 times greater than pre-stimulus levels. The frequency structures of the corresponding EEG reactions were divided into discrete frequency subgroups, including the traditional (1-30 Hz) and the gamma ranges (30-80 Hz) as well as higher-frequency components (80-200 Hz). In some cases, the greater proportionate increases in power occurred in the high-frequency band.