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Degree of manifestation and synchronization of rhythmic alpha-range components in various cortical areas was studied in healthy adult subjects in conditions of controlled computer experiment by spectral-correlation method of EEG analysis during directed attention previous to discrimination of tactile, auditory and visual stimuli. The obtained results show that in preparation for discrimination of heteromodal stimuli, specific reconstructions take place of alpha-range electrical activity determined by signal modality. These changes are expressed in a local increase of the degree of synchronization of alpha oscillations in those projection and associative brain areas which are connected with the analysis of the given stimuli. Functional significance of these reconstructions is seen in the fact that they are significantly more expressed at correct recognition. A hypothesis is suggested about participation of the alpha-range in neurophysiological mechanisms of directed attention.

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In an automatized experiment, with a computer on line, amplitude-temporal parameters of evoked potentials (EPs) to purposive and non-purposive stimuli (digits), were analyzed in normal and mental retarded children. At unilateral stimuli presentation to the left or right visual half-fields EPs were recorded simultaneously in projection, TPO, parietal and central areas of the left and right hemispheres. It has been shown that in normal children, differential involvement of projection and associative structures in the analysis of sensory information takes place in both hemispheres. The amplitudes of most EP components in the range of 100-400 ms to the purposive stimuli are higher than to the non-purposive ones. Considerable similarity of EPs developing in response to ipsi- and contralateral stimulations of visual fields ("direct" and "transmitted" EP) is observed. In mental retarded children significant changes are revealed in intra- and interhemisphere organization of the process of perception of purposive and non-purposive stimuli. In the right hemisphere structures there are no differential EP reactions to the two types of stimuli. Significant, in comparison with the norm, prolongation of the latencies of most EP components is noted, especially in the structures of the left hemisphere, to the purposive stimuli. In the process of perception, changes are seen of the integration of functions of both hemispheres. The totality of disturbances of systemic brain organization at perceptive activity in mental retarded children may reflect neurophysiological mechanisms of mental deficiency.

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Visual EPs of the occipital, parieto-temporal-occipital, parietal and central areas of the left and right hemispheres in response to unilaterally presented stimuli (figures) were analyzed in normal and developmentally backward children. In tasks of detection and recognition of the signal, developmentally backward children manifested a lowered reactivity of associative cerebral structures, especially of the left hemisphere, during perceptive activity, and a changed, in comparison with normal, interhemispheric interaction in processing of sensory information. It is suggested that properties of brain system organization during perceptive activity reflect to a certain extent neurophysiological mechanisms of disturbance of cognitive processes in developmentally backward children.

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Synchronized activity of alpha frequency recorded from a number of dog brain formations in the initial stages of postischaemic (postresuscitation) restoration was studied. Using the methods of destruction and elimination it was shown that the amygdaloid nuclei were the main source of such activity. Analysis of the general and particular coherence functions at the frequencies of alpha-like activity has shown that subcortical formations (thalamus, nucleus caudatus) become secondarily active sources of the generation of the bursts and of their generalization in the brain. Investigations and available literature lay the basis for the hypothesis that the activity observed in experiments and the activity described during postresuscitation alpha-pattern coma in humans have similar mechanisms of development and are, probably, identical.

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Proceedings from the analysis of known experimental data on theta-rhythm (fusiform activity) a determinate model of its generator is proposed. It is based on the mechanism of beats frequencies. The model consists of 2 united identical moduli generating harmonic (rhythmical) oscillations alpha-rhythms of approximating frequencies v1 and v2 = v1 + delta v. The working regime of the generator is determined by the trigger pulse frequency. The proposed quantitative relationships between theta-rhythm parameters--T, n and frequencies of constituent oscillations v and delta v are checked up by analysing oscillograms of barbiturate activity in EEG of dogs. The results obtained are in favour of determinate rather than stochastic mechanism of theta-rhythm.

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The role played by the amygdaloid nucleus, caudate nucleus, thalamus and brain cortex in propagation throughout the brain of generalized limbic alpha-like activity recorded on the EEG in the early postresuscitation period was studied in experiments on dogs resuscitated after a 13-15-minute circulatory arrest. Destruction or pharmacological inhibition of both amygdaloid nuclei resulted in disappearance of alpha-like activity from all the test structures. Coherent analysis showed that the caudate nucleus and thalamus, in particular, take an active part in propagation of alpha-like waves of biopotentials from the amygdaloid nucleus to other brain structures.

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