CEREBRAL REPRESENTATION OF PENILE ERECTION

Abstract

An investigation is being undertaken to learn the cerebral representation of penile erection. This first paper reports the results of systematically exploring and electrically stimulating midline cortical and subcortical structures from the septum to the mammillary bodies. Observations have been made on 19 chronically prepared squirrel monkeys (Saimiri sciureus) and 10 acute preparations. Positive loci for erection are found in parts of three corticosubcortical subdivisions of the limbic system: (i) they coincide with the known anatomical distribution of hippo-campal projections to parts of the septum, anterior and midline thalamus, and hypothalamus; (ii) they are located in respective parts of the anatomical system comprising the mammillary bodies, mam-millothalamic tract, anterior thalamus and cingulate gyrus; (iii) still other loci are found in the gyrus rectus, medial part of the medial dorsal nucleus and regions of their known connections. The inferior thalamic peduncle which contains projections from the medial dorsal nucleus is strongly positive. The medial septopreoptic region and medial part of medial dorsal nucleus appear to be nodal points for erection. Positive loci are followed along the course of the peri-ventricular fiber system and of the medial forebrain bundle. The latter appears to be the major descending pathway. Electroencephalographic findings suggest that the hippocampus modifies the excitability of structures involved in penile erection. Data are given pertaining to frequency-amperage curves and optimum parameters of stimulation. A number of autonomic and somatic manifestations elicited in conjunction with penile erection are described. The findings on localization are discussed from the standpoint of evolutionary changes within the three aforementioned corticosubcortical subdivisions of the limbic system that possibly reflect differences in the role of olfactory and visual influences in sexual behavior.