The spatial organization of biopotentials in the cerebral cortex of 23 subjects who were students at the Faculty of Graphic Arts ("professionals") as well as 39 subjects lacking systematic experience of visual images ("non-professionals") was compared with the aim of identifying EEG correlates of the experience of visual images (image formation) in humans. Changes in measures of the spatial organization of biopotentials (spatial synchronization, spatial disordering, coherence, and spectral power) were analyzed as subjects mentally composed visual images consisting of two simple graphic elements - right angles and oblique lines. The total number of image elements increased in each of four sequential tasks, from a number which could be analyzed at the conscious level (4-7 elements) to a number exceeding analysis at the conscious level (8-16). Intergroup differences, particularly increases in the spatial disordering of biopotentials (non-linear processes), were detected when large numbers of elements were used (tasks 3 and 4). This measure increased more markedly in professionals than in non-professionals. Changes were significant in the anterior areas of the right hemisphere. Spatial synchronization of biopotentials (linear processes) increased in non-professionals in the posterior areas of the right hemisphere. Coherence and spectral power increased in professionals in a larger number of narrow-band EEG frequency subranges than in non-professionals. These data show that experience of visual imagery results in a more complex neurodynamic process during the activity, with non-linear dynamics and a multitude of EEG resonance systems at different frequencies.
The characteristics of the spatial organization of biopotentials in the neocortex during the mental creation of original and standard mental images were studied. Intra-and interhemisphere coherence associations at different EEG frequency ranges were assessed, along with linkages between relative changes in measures of linear (correlation coefficient) and non-linear (multiple entropy) processes between different areas of the neocortex. Creation of original thoughts was found to be associated with a significantly smaller number of associations with decreased coherence in the high-frequency alpha range between distant points than on formation of standard images. On formation of original images, the number of concordantly functioning pairs of cortical areas and the mean level of synchronization between them were greater in terms of linear processes than on formation of standard images, while in terms of non-linear processes, the number was, conversely, smaller. The correlational relationships between changes in different cortical areas for both types of process were only positive on creation of original images, while creation of standard images yielded both positive and negative correlations. These data lead to the conclusion that the spatial organization of biopotentials during the mental creation of original and standard images differs in terms of the cortical distribution of concordant changes in linear and non-linear processes, their levels of linkage, and the nature of interhemisphere interactions. Data on differential interhemisphere interactions in the diagonal and central bilateral profiles suggest the radial representation of visual imagination.
Data were obtained in experiments on nonimmobilized and nonanesthetized rabbits, during the development of an analog of a CR, with recording of the response of the pyramidal tract, suggesting temporal specificity in the manifestations of membrane and synaptic plasticity, the participation of these mechanisms in both representations of the combined stimuli, and primarily unidirectional changes in the degree of their participation in these points of the cortex. It is concluded that temporary membrane plasticity creates conditions through the mechanisms of synchronization and summation for the passage of excitation from the sensory link to the motor output of the new connection. The gradual reorganization of excitatory and inhibitory connections to the output elements of the conditioned reflex act, determined by the mechanisms of synaptic plasticity, determine and strengthen the specialized character of the developed reaction.
The calculation of the coefficient of correlation between changes in the direct (D) and monosynaptic (I) components of the pyramidal tract (PT) response made it possible to establish the presence of a positive linear association between conditioned reflex changes in synaptic efficiency and the shifts in cellular excitability observed at the same time. The coincidence of the maximal strength of this association with the greatest increase in cellular excitability which is dependent on the activation of motivatiogenic structures points to the role of these subcortical structures in the launching of intracellular reactions which leads to the formation of the overall molecular substrate which underlies interaction of membrane and synaptic mechanisms. The preceding of the greatest enhancement of synaptic efficiency by the maximal manifestation of the interaction attests to the contribution of this process to the manifestation of the principal mechanism of the conditioned reflex (CR).
The characteristics of the temporospatial organization of cerebral cortical potentials at different levels of genetically determined emotionality were analyzed by constructing topograms of instantaneous EEG levels in the inbred rat strains MR and MNRA. Two parameters were calculated for each topogram: the total level and the similarity coefficient. Power spectra were calculated for the values and these were found to change in an oscillatory manner. Interstrain differences were found in the correlated changes in total levels and similarity coefficients, in the durations of changes in the total level, which were more marked than those of similarity coefficients, and the nature of interhemisphere asymmetry. In MR rats, the power spectra of both measures showed significant peaks with modes at 2.0, 6.5, and 9.0 Hz. In MNRA rats, peaks in the spectra of these measures both coincided (2.0 Hz) and differed (7.0 Hz in the spectrum of the total level and 3.0, 4.5, and 6.0 Hz in the spectrum of the similarity coefficient). These data suggest different types of functioning of the reticulothalamocortical and hippocampocortical systems in rats of these strains.
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