Analysis of neocortical electrical responses evoked by stimulation of various hypothalamic structures

Evoked potentials (EPs) and extracellular unit activity were recorded in various parts of the neocortex of unanesthetized cats immobilized with succinylcholine. During hippocampal stimulation EPs of maximal amplitude are recorded in the anterior sigmoid gyrus with a latent period (LP) of 0.5-2.5 msec. The first component is a fast positive spike with a duration of about 1.5 msec. In the middle suprasylvian gyrus, hypothalamo-cortical (HC) EPs have a monophasic surface-negative configuration and are recorded after an LP of 2-6 msec. HC EPS in the anterior sigmoid gyrus can bind a rhythm of stimulation of up to 200 pulses/sec and are characterized not only by high functional mobility, but also by the property of posttetanic potentiation. The main positive wave appears to a testing stimulus with an interval of 7-10 msec. Complete recovery of all components of HC EP takes place at an interval of 50-150 msec. In response to the conditioning stimulus a biphasic change in excitability of the neurons is observed in the association areas of the anterior sigmoid and middle suprasylvian gyri of the neocortex. The maximal number of responding neurons in the deep layers of the cortex discharges in the period of development of the initial spike and the main positive wave of the HC EP.