[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.

[The functional role of neocortical gamma activity in the process of interrelations between different areas].

In the context of understanding of the mechanisms of cognitive human accounting functional role in these processes of neocortical gamma activity, the science progress of the 21st century at least three new logically related directions are outstanding to: 1) combination with intracranial recordings by functional magnetic resonance imaging (fMRI) has indicated a closely correlation between the level of power of high gamma-band (90-150 Hz) at corresponding localization and the level of blood oxygenation (responses BOLD; blood oxygenation level dependent), which provides an estimate of the dynamics of power in aspect of metabolic resources; 2) results parallel evaluation of parameters gamma activity (frequency, bandwidth, amplitude) in combination with the size of BOLD responses and the GABA concentration as measured by magnetic resonance spectroscopy, formed the basis of hypothesis about the individual peculiarities (specific features) of the subject (trait); 3) new methods of measuring the phase synchrony of gamma frequencies has created the phenomenon of cross-frequency interaction (cross-frequency coupling, CFC) between phases of gamma oscillations with theta, alpha waves. This phenomenon is considered by some authors as the basis of interrelations of different separated networks, possibly providing approach to understanding of various aspects of defining the mechanisms of cognitive processes.

[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.

[Functional heterogeneity of gamma-band cortical potentials].

A review. The problem of the functional significance of gamma-band EEG in different cognitive paradigms, including the aspect of the gamma-band heterogeneity (different origin and functional significance of "low gamma" and "high gamma").

[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.

[Possibilities of the metric estimation of gamma activity in human EEG].

A review. Studies in the period of 2009-2011 are discussed, in which a new phenomenon in human EEG was found out, i.e., personal (individual) features ofneocortical gamma activity in parameters such as amplitude, frequency and width of the gamma band. This phenomenon was revealed in induced responses to visual stimuli in people under conditions of repeated research (after different time intervals - hours, weeks, months). The findings suggest the necessity of development of the metric system for assessment of this phenomenon and corresponding estimation of personal features of the gamma band and their stability (reliability), which would allow interindividual differences to be revealed.

[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.

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.

[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.

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.

[The phenomenon of spatial synchronization of the brain potentials in a broad frequency band 1-250 Hz].

A review. The article dedicated to the centenary of academician Mikhail Nikolaevich Livanov briefly outlines the history of development of his original concept of the functional significance of the brain potential's spatial synchronization phenomenon as a possible way of studying systemic organization of the brain electrical activity. The new parameter of "space" introduced into neurophysiology by M. N. Livanov made it possible to research the earlier unknown aspect of the brain activity. Livanov's ideas have been developed in many studies of the late decades of the XX century. In the review, much attention is given to specific functional significance of this phenomenon in a broad frequency band 1-250 Hz, especially, during instrumental learning. Energy (power spectra) and coherent-phase characteristics of cortical potentials in traditional (1-30 Hz), gamma-(30-80 Hz) and high-frequency (80-250 Hz) bands are compared. The problem of linear and nonlinear processes in the organization of the brain potentials is mentioned.

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.

[Electrographical correlates of adequate and erroneous responses caused by conditioned signals of different functional sign during instrumental conditioning in dogs]. / Elektrograficheskie korrelyaty adekvatnykh i oshibochnykh otvetov, vyzyvaemykh uslovnymi signalami raznogo funktsional'nogo znaka, pri instrumental'nom obuchenii u sobak.

Power spectral (in the broad frequency band of 1-225 Hz) of short-term (less than 1 s) EEG reactions were studied in dogs in the course of instrumental food conditioning. These reactions appeared in different cortical areas in response to differentiating signals under conditions of both adequate and erroneous responses. The EEG power of such reactions was several times lower as compared to responses to positive signals, mainly, at the expense of the frequencies in the band of 90-225 Hz (the power of which was higher than that of the traditional band of 1-30 Hz and the gamma band of 30-80 Hz). The frequency composition of EEG reactions accompanying adequate responses was defined, mainly, by discrete subgroups of high-frequency components. During erroneous responses, the discrete structure of the corresponding EEG reactions was broken.

Studies of selective attention in dogs using the coherence-phase characteristics of cortical potentials over a wide range of frequencies, 1-220 Hz.

The state of selective attention formed during operant food-related behavior was studied using the coherence-phase characteristics between potentials in several areas of the neocortex at frequencies of 1-220 Hz. Functional groups were identified among the areas compared, which appear to have priority for this state. The temporal relationships between potentials in these groups were established from values for coherence functions at a particular optimum level (0.7) mainly in the band 1-15 Hz and the high-frequency range 40-200 Hz. The phenomenon of synchronicity appeared at phase shifts close to zero, while at significant phase shifts the phenomenon of non-synchronous time relationships with defined spatial directions was seen in the high-frequency range.

Studies of selective attention in dogs using the energy characteristics of neocortical potentials in the frequency range 1-220 Hz.

Experiments were performed in dogs to study the state of selective attention formed during operant food-related training and apparent during interstimulus intervals as a state of tense expectation of the conditioned signal. Electrical activity in various parts of the neocortex, in both hemispheres, was analyzed in the frequency range 1-220 Hz (epidural electrodes) using Fourier transforms. The electrical activity of the motor area of the right hemisphere showed a predominance of high-frequency (40-200 Hz) components, as did the visual and parietal areas of the left hemisphere. The state of selective attention was associated with a different functional mosaic in the organization of neocortical electrical activity.