Bioelectrical changes of the heart cycle induced by stimulation of diencephalic regions

The production of alterations in cardiac function by stimulation of diencephalic regions has been reported in the past. These alterations have been considered indicative of the existence of central regulatory mechanisms acting upon the contraction of the heart muscle. The principal purpose of the present study was to clarify further some aspects of this functional relationship. The experiments were carried out in cats under the action of a curarizing agent. Electrodes were stereotaxically oriented to stimulate, in a point-to-point exploration, the ventral structures of the diencephalon. Diencephalic influences upon the heart cycle are revealed by the analysis of the electrocardiogram under stimulation of hypothalamic and subthalamic areas. Changes in rhythm, as well as changes in the configuration of the electrocardiographic wave components, are obtained by stimulation at a number of locations. Effects of sympathetic activation, such as tachycardia and increase in the amplitudes of the QRS complex and the T wave, are much more commonly and consistently seen than those resulting from activation of the parasympathetic system. A zone is delimited from which influences on the heart are most readily exerted. This zone covers most of the lateral and posterior hypothalamus, the zona incerta, and the tegmental fields of Forel. Excitation of these areas frequently results in the activation of abnormal foci of impulse formation in the myocardium.