[An analysis of the electrical responses of the neocortex evoked by stimulation of different hypothalamic structures]

Evoked potentials and extracellular spike activity during stimulation of the posterior, lateral, anterior, and ventro-medical hypothalamus were recorded in different areas of the neocortex in unanesthetized cats. Hypothalamo--cortical evoked potentials (HC EP) of maximal amplitude are generated in gyr. sigm. ant. with 0.5--2.5 msec latency. The responses are of positive--negative configuration and often a fast spike--like defiction appears at the positive phase. EP in gyr. suprasylv. med. are initially negative and of 2--6 msec latency. Most effective is stimulation of the posterior and lateral hypothalamus, HC EP in gyr. sigm. ant. following the frequency of stimulation up to 200/sec and being characterized not only by a high "functional lability" or reproducibility but also by the ability of posttetanic potentiation. With the aid of paired stimuli, the early fast component of the EP in the sensorimotor cortex was shown to appear at an interval of approximately 2 msec. HC EP entirely recover 50--150 msec after the conditioning stimulus. The recovery cycle is biphasic and reflect, a biphasic change of the excitability of neurons in gyr. sigm. ant. and suprasylvian associative areas of the cortex. The latency of evoked discharges of some neurons of the sensorimotor cortex during stimulation of the posterior hypothalamus, is 0.8--1.5 msec, which suggests the existence of a monosynaptic pathway for the hypothalamo--cortical discharges. The maximal amount of neurons in deep layers of gyr. sigm. ant. respond during development of the early and the main positive deflections of HC EP.