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Biomedical subjects

V N Dumenko

Publications and source records attributed to V N Dumenko.

At least 37 records · Page 2Linked to original sources
PubMedDate not supplied

Dynamics of high-frequency (up to 200 Hz) components of brain electrical activity during learning reflect the functional mosaicism of the neocortex.

This study was undertaken with the aim of identifying frequency bands with correlated changes in the spectral power amplitudes of brain electrical activity, including high-frequency components (the 1-200 Hz band) in four dogs, using one-dimensional analysis. Factor and cluster analysis of the spectral densities of various parts of the cortex and the olfactory bulb were carried out. The ratios of factors in different parts of the brain, both in terms of the proportions of the total dispersity and in terms of weightings, provided data on regional and individual differences in electrical activity. During learning (development of a motor habit consisting of pressing a feeder pedal), the factor organization of electrical activity became more, complex, particularly in the high-frequency part of the spectrum (40-170 Hz). The changes consisted of the appearance of narrower frequency sub-bands, each of which was present at high weighting (0.7-0.9) for one of the factors. The use of high-frequency components allowed functional mosaicism of the neocortex to be detected.

Animals↗
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Assessment of the high-frequency components of brain electrical activity using inhomogeneity indexes.

Inhomogeneity indexes were developed, and were found to be quite reliable indicators of the presence of short-term high-frequency bursts in the electrical activity of the dog brain, and were also sensitive discriminators of quasi-homogeneous fragments in terms of the level of "general activation." Studies demonstrated that the values of these coefficients reflect the individual features of animal brain electrical activity, as well as its dynamics during the development of conditioned operant feeding reflexes. At the same time, these indexes did not reveal any regional variations. Using the construction of an inhomogeneity spectrum as an example, an approach to identifying similar numerical characteristics, also based on traditional harmonic analysis (Fourier transformation), is discussed.

Animals↗
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Bursts of high-frequency synchronized electrical activity in the dog neocortex during food-related operant conditioning.

Bursts of high-frequency (HF, 80-90 Hz, 70-80 microV) oscillations in the electrical activity (EA, 1-200 Hz) of the dog neocortex were studied during operant conditioning. These bursts of HF oscillations appeared in the EA of interstimulus intervals at the generalization stage on a background of dominant oscillations of lower frequency and amplitude (10-40 microV). Use of a new strategy for primary analysis of EA production (specifically, a coefficient of inhomogeneity) allowed amplitude-frequency inhomogeneity of the EA to be estimated, with isolation of bursts of HF oscillations. Use of an original nonharmonic analysis, consisting of expansion of EA waves into a system of half-waves which were used to construct distribution maps, revealed the regional properties of bursts of HF oscillations. The results of these investigations supplement previous data obtained using other methodological approaches (Fourier transformation and spectral density factor analysis). The properties of bursts of HF oscillations observed here provide evidence for the differential involvement of cortical areas (even close-lying areas separated by distances of 3-5 mm) in the spatial-temporal organization of potentials typical of this conditioning paradigm.

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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.

Acoustic Stimulation↗
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[The mosaic structure of the high-frequency range of neocortical electrical activity in dogs].

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.

Acoustic Stimulation↗
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[Selective attention in dogs from energy characteristics of neocortical potentials in the 1-220 Hz band].

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.

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[Study of selective attention in dogs by coherent-phase characteristics of cortical potentials in the broad frequency band 1-220 Hz].

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.

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[Formation of linear relations of potentials in the dog neocortex in a dynamic stereotype].

During elaboration of a stereotype system of defensive conditioned reflexes in dogs (Pavlov dynamic stereotype), a correlation spectral analysis was made of electrical activity in the neocortex. With a stable dynamic stereotype, substantial changes of background electrical activity were observed in the interstimuli periods, manifested in a significant growth of linear relations of cortical potentials at certain frequencies. This was expressed in separation from the wide-band random process (involving background activity before the formation of the dynamic stereotype) of definite, relatively narrow ranges of frequencies which formed the high coherence of the processes. No such changes of electrical activity were observed in conditioning without a stereotype; this points to special mechanisms of the dynamic stereotype, which differ from those of ordinary conditioned reflexes.

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[Functional significance of high-frequency components of brain electrical activity in the processes of gestalt formation].

A review. Current views of the so-called binding problem, which considers hypothetical mechanisms of perception of sensory stimuli and formation of their corresponding Gestalts (internal images) are discussed. The mechanism of intensification of synchronized reactions of cortical electrical activity in the gamma band frequency (30-80 Hz) is the basis of the most popular point of view of "binding". The article considers the evidence for the functional significance of the high-frequency components exceeding the gamma-range (to 200 Hz) obtained by the author, the origin of these oscillations, and conditions of their focal derivation. The problem of "binding" and stages of instrumental conditioning (a stimulus, perception of the stimulus, and its transformation into a signal) as well as significance of the context in learning and formation of tonic states ensuring the realization of phasic reactions is discussed. Forms of "binding" at the final stage of conditioning (selective attention) are considered. The question is posed as to whether "binding" is exhausted only by the mechanisms of synchronization of activities of large neuronal populations and only in the frequencies of the gamma range.

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[A computer analysis of EEG intersignal reactions during the the acquisition of conditioned motor-food reflexes in dogs].

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.

Action Potentials↗
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[Electrographical correlates of adequate and erroneous responses caused by conditioned signals of different functional sign during instrumental conditioning in dogs].

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.

Animals↗
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[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.

Animals↗
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[A new method of breaking down the electroencephalogram into a system of oscillations that allows for the analysis of EEG phenomena of different durations].

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.

Algorithms↗
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[The significance of the high-frequency components in the cortical potentials of dogs in a study of learning mechanisms].

Electrical activity was studied of five different regions of dogs neocortex in inter-stimuli periods in the process of learning of motor habit of pressing the feeder pedal. Epidural electrodes were used. The processing was performed by means of correlation-spectral analysis in a wide band of 1-256 Hz. Values of cross-correlation coefficients, spectra of power, coherence and phase shifts were obtained. In the process of the habit consolidation the high frequencies power increased significantly (within the limits from 60 to 150-170 osc/sec), as well as the part of high coherence (over 0.75), falling on these limits, with low phase shifts. Relatively slow-wave oscillations (1-20 osc/sec) underwent changes of considerably lesser degree. A greater locality of high frequencies (in comparison with the traditional range of 1-20 Hz) was shown. The question of the nature of high frequency EEG components is discussed.

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[Spectral-correlative characteristics of the EEG reactions preceding conditioned reflex motor reactions in dogs].

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).

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[High-frequency components of cortical potentials and their phase-coherent characteristics during the acquisition of motor-food conditioned reflexes in dogs].

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.

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