Influence of the posterior hypothalamus on the visual cortex in various states of the reticular formation.

It has been demonstrated in chronic experiments on wakeful rabbits that the stimulation of the posterior hypothalamus by a single electrical stimulus leads to the formation in the visual cortex of a short-latency response which exerts a substantial influence on the formation of the reaction to light stimulation. Depending upon the intervals between the hypothalamic and light stimuli, an initial suppression of the response is observed (1-15 msec), a subsequent selective facilitation of its positive component in the presence of the simultaneous suppression of the negative (20-100 msec), and the complete recovery of the response (200-300 msec). Aminazine and amizil do not alter the directionality of the influence of the stimulation of the posterior hypothalamus on the responses of the visual cortex; however, they do significantly attenuate the degree of expressivity and the dynamics of this influence. Experiments involving local foci in the mesencephalic reticular formation (strychnine, KCl) attest to the inhibitory influence of the latter on the activity of the hypothalamocortical input. The role of the phasic mechanism of hypothalamic control in the realization of the perceptual function of the visual cortex is considered.