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Quantitative characteristics of afferent flows coding information from a number of receptors were obtained by the gliding impulses method. The frequency spectrum of activity in a cutaneous nerve, the relative numbers of active Abeta, Adelta, and C fibers and their distribution by impulse transition frequency during stimulation of the cat's skin with pins and needles were determined. The afferent flow recorded in the nerve during pricking of the skin is characterized by high density, due to the number of excited fibers and the frequency of activity in them. The higher density of the afferent flow during the application of a painful than of a painless stimulus is mainly due to activity in C fibers. Unmyelinated fibers subjected to the action of the same stimulus and of chemically active substances liberated from the cells during tissue injury are excited directly and generate high-frequency spikes which increase the flow density in the nerve. The number of active myelinated fibers and the spike frequency during the action of a painful stimulus are only a little greater than the corresponding characteristics of the afferent discharge during painless stimulation.

High-frequency electrical stimulation of the-posterior hypothalamus applied 10-20 days after the sectioning of the brain stem at the level of the anterior frontal margins of the anterior coliculus results in the preferential activation of the ipsilateral neocortex. When unilateral lesions are placed in the posterior hypothalamus, the predominance of synchronous activity in the ipsilateral neocortex is observed. In the premesencephalic preparations, weak single electrical stimulation of the posterior hypothalamus provokes spindles in the ipsilateral portions of the frontal cortex. At more intensive single stimulation of the posterior hypothalamus there occurs diffuse appearance of spindles in different neocortical areas. Besides the preferential unilateral effect, the influence of the posterior hypothalamus is more prominent in the frontal than in the occipital regions of the cortex. It is suggested that the posterior hypothalamus exerts its influence on the neocortex through the thalamic nuclei.

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