Under the conditions of extracellular recording of action potentials, the influence of proposed neuromediators on the structure of background impulse activity of neurons of various regions of the cerebral cortex was studied. Computer analysis of the statistical parameters of impulse flows revealed the presence of a fundamental difference between the effects of neuromediators of cortical and subcortical origin. It was demonstrated that prolonged application of serotonin and noradrenalin evokes a change in structure of cortical neuron impulse activity more complex than the simple inhibition and excitation characteristic of acetylcholine or GABA. Different types were found of the reaction of neurons to the same monoaminergic stimulus, types whose characteristic feature is the dependence of the end result of the influence on the initial level of excitation in the neuron examined. The fundamental difference between the effects of preparations studied in the visual and sensorimotor regions of the cortex was not discovered. The data obtained are considered from the point of view of the modulating role of the biogenic amines in the regulation of the level of excitation of cerebral cortical neurons.

An analysis of the influence of the posterolateral hypothalamus, which elicits positive reactions in behavioral testing, and of the midbrain raphe nuclei, on the plastic properties of the neurons of the visual cortex, was carried out in acute experimental conditions on diplacin-immobilized rabbits, based on a model of cortical trace processes. The different types of change in the reactivity of cortical cells under the influence of rhythmic sensory stimulation are described. The results of statistical analysis point to a dependence of hypothalamic and serotoninergic influences on the initial reaction of neurons to sensory stimulation. It is demonstrated that the plastic changes in the activity of cortical neurons reveal similar features under the influence both of the "positive" emotiogenic zone of the hypothalamus and of the midbrain raphe nuclei. Similar regularities are observed also in an analysis of the interaction of cortical neurons which were recorded in one microvolume identified by the method of cross-interval histograms.

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