The effect of pre-test verbal instruction on spatial organization of cortical electrical activity

Analysis of coherence of cortical electric activity performed in 30 healthy subjects revealed changes in the spatial organization of cortical electric activity after listening the instruction, i.e., loading the explicit working memory with a sequence of operations of the cognitive task to be solved in the course of the experiment. Comparison of instructions presenting several cognitive tasks showed that greater load of the working memory is associated with higher coherence of cortical activity, especially, in the parietotemporal and occipital areas.     

Dependence of the organization of human brain electrical activity on hemispheric dominance

In healthy subjects, in a state of relative rest, with different individual profiles of asymmetry (20 right-handed and 10 left-handed subjects), a greater conjunction of electrical brain processes (estimated by mean EEG coherence levels) has been found in the dominant hemisphere as compared to the subdominant one, more distinctly expressed in the right-handed subjects. The maximum degree of interhemispheric asymmetry of the EEG coherence is observed in the posterior associative cortical areas. Specific interhemispheric theta-range differences are revealed as compared with other EEG frequency bands. Greater values are obtained of the correlation of the EEG symmetrical hemispheres points in the whole frequency band and in alpha- and beta-ranges in the right-handed subjects than in the left-handed ones.     

Steroids and electrical activity in the brain

Corticosteroid hormones can enter the brain and bind to two receptor subtypes: the high affinity mineralocorticoid receptor (MR) and the glucocorticoid receptor (GR) with approximately 10-fold lower affinity. Under physiological conditions the degree of receptor occupation will range from a predominant MR occupation (at the beginning of the inactive period, under rest) to concurrent activation of MRs and GRs (at the circadian peak and after stress). With in vitro electrophysiological recording techniques we observed that neuronal excitability in the CA1 hippocampal field is under a long-term control of MR- and GR-mediated events. The predominant occupation of MRs is associated with a stable amino acid-carried synaptic transmission; calcium- and potassium-currents are small, as are the responses to biogenic amines. Occupation of GRs in addition to MRs results in a gradual failure of CA1 neurons to respond to repeated stimulation of amino acid-mediated input; ionic conductances and responses to biogenic amines are large. In general, electrical properties recorded when both MRs and GRs are unoccupied (i.e. after adrenalectomy) resemble the responses observed when both receptor types are activated. The corticosterone dependency of electrical properties is thus U-shaped. We conclude that MR occupation may be responsible for the maintenance of information processing in the CA1 field and the stability of the circuit. Additional activation of GRs will initially suppress synaptic activity, but may eventually result in an increased instability and even vulnerability of the neuronal networks.     

The impact of experimental instruction on changes in EEG power during verbal creative thinking in men and women

Features of EEG pattern during verbal creative thinking depending on experimental instruction were studied in men and women. Spectral power density was analyzed in six frequency bands (4-30 Hz). Performance of a creative task produced an increase in the power of theta (4-6 Hz) and beta2 (20-40 Hz) components and decrease in the power of alpha (8-13 Hz) and betal (13-20 Hz). Changes in the alpha and betal bands were observed, predominantly, in the posterior areas, whereas power of the thetal and beta2 bands increased in the anterior areas. Independently of instruction, women demonstrated greater synchronization in the theta1 band than men, whereas in men the desynchronization in the alpha2 band (10-13 Hz) was more pronounced. When the subjects were instructed to create original sentences, a widespread decrease in the EEG power was observed in the band of 8-30 Hz as compared to instruction "to create sentences". Thus, the instruction-related changes in EEG power were not gender-specific. They may reflect neural activity mediating selective attention.     

Brain mechanisms of imagination in solving creative verbal tasks

The brain’s mechanisms of imagination were studied using electroencephalography (EEG) spectral analysis in student actors and student non-actors under three experimental conditions: when they generated coherent stories on the basis of art reproductions (STORY task); listed the details of art reproductions presented (DETAIL task); and performed simple arithmetic calculations while observing a neutral background (COUNT task). Statistical analysis showed that, in α₁ (7.5–10 Hz) and α₂ (10–12.5 Hz) frequency bands, in both groups, execution of the STORY task, in contrast to the DETAIL task, was accompanied by significantly higher spectral power (synchronization) in most of the cortical areas studied; while, the contrasts STORY-COUNT and DETAILS-COUNT, were associated with a decrease in the EEG’s power (desynchronization) in all of the areas studied. Topographic mapping of the EEG’s power showed that, in both groups, maximal differences between the STORY and DETAILS tasks were related to the central parietal area. Maximal differences between the STORY and COUNT tasks, as well as those between the DETAILS and COUNT tasks, were related mainly to the occipital areas. Based on these findings, we consider parietal areas to be stable elements of integrated brain mechanisms underlying verbal creativity in actors and nonactors. Comparing our data with previous studies, we suggest that the parietal areas are involved in the selective inhibition of visual information processing during the involvement of brain structures in the processes of imagination.     

Plasticity in the visual system: role of neurotrophins and electrical activity

We report recent results concerning the action of neurotrophins on the development and plasticity of the visual system of mammals and in particular of their visual cortex. It has been demonstrated that NGF prevents all the effects of monocular deprivation during the critical period. BDNF, that in part also prevents the effects of monocular deprivation, has the interesting additional property of accelerating the development of inhibitory processes. In transgenic mice overexpressing BDNF only in the cortex, the critical period for plasticity initiates a week earlier and presents a precocious closure. Visual acuity also develops much before than in normal animals. These phenomenological observations are paralleled by a precocious increase of inhibitory synapses and inhibitory currents in pyramidal neurons. LTP, tested by stimulation of the white matter, recording in layers 2 and 3 of the visual cortex, presents modifications correlated with the alterations observed in the critical period. Last we report the finding from in vitro and in vivo experiments that MAPkase (Erg 1 and 2) is the molecular chain of events driven both by light and neurotrophins, likely at the bases of the phenomena of plasticity observed during the critical period.     

The role of the extralogical form of thinking in cognitive activity

The aim of the study was an attempt to record neurophysiological processes connected with the mechanism of subconscious brain activity. Created in the laboratory method of construction of a topographical map of electrical processes interactions in 24 recorded points was applied. The obtained data testify that identification of evident and latent images in "double image pictures" is accompanied by similar relief of topomaps of interactions. Effect of "sudden vision" of latent image in a manner of "insight" is gradually prepared neurophysiologically, but is not realized by the subject and only at the last stage reaches the consciousness and is verbalized.     

Utilization of factor analysis for the evaluation of ontogenetic and functional changes in the electrical activity of the brain

The tendency of the index, amplitude and its dispersion during the year is opposite to the age-dependent tendency of changes in these indices and points to a chronic component of mental fatigue. It is very important that in the second half of the school year the dispersion of the EEG amplitude increases in all sections of the brain and in all frequency ranges: an increase in EEG amplitude dispersion in parallel with an increase in the amplitude itself indicates that the process of synchronization and the ultraliminal inhibition connected with it in different sections of the brain and in various frequency ranges of the EEG is not stagnant or inert but mobile and instable and can therefore be relatively easily removed by special hygienic measures. As an example of the latter we can mention the use of a special regime of exercise (Yu. M. Pratusevich et al., 1975), addition of supplementary factors of nutrition to the diet of the time the children spend in the fresh air engaging in outdoor games (Yu. M. Pratusevich, 1964).     

Cerebral organization of verbal action in stutterers

A comprehensive interdisciplinary study of the cerebral mechanisms of readiness for speech was performed based on a complete neuropsychological examination according to A.R. Luria with qualification and quantification of the detected symptoms and electrophysiological data by an original method of recording and localization of the potentials synchronized with the preparation for speaking. The data on stutterers were compared with those on normal subjects and showed that stuttering is not an isolated (purely peripheral) speech disorder but is a component of a syndrome consisting of specific mnestic, neurodynamic, and motor defects that reflect dysfunction of postfrontal and median structures of the brain (functional blocks I and III according to Luria). Differences between normal and stuttering subjects in the potential related to readiness for speech were associated with the activity of deep median structures (the pons and brainstem), right subcortical nuclei, the right frontal cortex, and the left mediotemporal cortex.Translated from Fiziologiya Cheloveka, Vol. 31, No. 2, 2005, pp. 13–17.Original Russian Text Copyright © 2005 by Vartanov, Glozman, Kiselnikov, Karpova.     

Crossintervalograms for analysis of electrical activity of the brain

A method of construction of crossintervalograms for electroencephalograms is proposed. Particular points or EEG fragments of particular shape are used as time-locked events, and the intervals between these reference points are analyzed. The method is theoretically substantiated. Examples of crossintervalograms constructed for EEG extrema and derivative EEGextrema are given. The information validity of these crossintervalograms is demonstrated and their features are indicated. Comparison crossintervalograms with crosscorrelograms is performed. The possibilities of further development and applications of a method are specified. It is suggested that the method will be useful for investigation of operative interaction of brain subsystems.     

Evoked frequency stabilization in the electrical activity of the cat brain

In this study, our previous results on the important relation between EEG and EPs were extended by experiments with chronically implanted and freely moving cats, which had electrodes at the acoustical cortex, inferior colliculus and reticular formation. During the experiments the frequency stabilization upon sound stimulation was shown in the frequency domain by comparison of the pre-stimulus power spectra and post-stimulus amplitude frequency characteristics. Comparative frequency domain analysis of about 75 EEG-EPograms (sample of spontaneous activities just prior to stimulation and single evoked potentials following the stimulation), which were recorded from all the brain nuclei mentioned above and from each of the 11 cats, was performed as follows: 1) Power spectra of the EEG-records prior to stimulus were evaluated. 2) Instantaneous frequency characteristics of single EPs were obtained by the Fourier transform. 3) Distribution of the amplitude maxima of the EP-frequency characteristics and the distribution of the EEG-spectral peaks were compared by plotting two types of histograms containing relevant spectral peaks before and after the stimulation. In a frequency range between 1–1000 Hz, the frequency distribution of the EP records from RF and IC were accumulated in narrow discrete frequency channels, whereas, the distribution of the spectral peaks of the EEG depicted frequency spread in broad channels. The frequency stabilization of the EP records from GEA, in the alpha frequency range, was also observed. This effect was described by a factor which we called as the Frequency Stabilization Factor. The results presented in this study showed that the frequency stabilization of the brain's electrical activity induced by sensory stimulation displayed a fluctuation leading to frequency stabilization factors between 0.95 and 5.00. The frequency stabilization and relevant power enhancement upon stimulation strongly support our contention that evoked potential results from the frequency stabilization of the spontaneous activity, triggered by stimulation.Supported by Grant No. TAG-345 of the Scientific and Technical Research Council of Turkey     

Recording electrical activity from the brain of behaving octopus

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