Blood pressure, pulse, and respiratory changes produced by stimulation of the hippocampus of the monkey.

Cardiovascular and respiratory changes resulting from systematic stimulation of the hippocampal formation of the monkey were recorded. Stimulation of the anterior portion of the hippocampus resulted in a marked depression or cessation of respiratory excursions, but without apparent changes in respiratory rate. Respiratory changes were minimal to absent when posterior regions of the hippocampus were activated. Anterior hippocampal stimulation resulted in an initial depression of blood pressure accompanied by a small drop in pulse rate, followed by a rise in blood pressure which lasted throughout the period of stimulation and then gradually returned to former levels. The duration of the rise in blood pressure following cessation of stimulation was directly correlated with hippocampal activity. Posterior hippocampal stimulation did not show the secondary rise in pressure, only the depression. Marked pulse changes occurred only when the hippocampal gyrus was secondarily activated or stimulated directly. The neuron pathways which mediated these responses fall into two general groups, the fornix system and a hippocampotemporal system or both. A hypothesis that both systems may be concerned in visceral responses is presented.