Well this is the start to the research. From this first article the visceral brain is said to be the oldest part of the human brain.
Mating, like feeding, takes place under a combination of nervous and hormonal control. Much of this control is mediated by parts of the nervous system within the "visceral brain", which is phylogenetically the oldest part of the human brain. It is comprised by a group of structures located in the inferior part of the forebrain and around it, called the hypothalamus, the hypophysis and the limbic system as well as the mesencephalon (the midbrain).
Despite the fact that sexual behavior in humans is controlled and driven by one of the most primitive parts of our brain, at the same time it is strongly influenced and modulated by learned experience, as well as by the social, ethnic and cultural environment; making it an unique blend of the physiological and the psychological spheres. In addition, what is considered "normal" and "abnormal" in human sexual behavior is highly variable across cultures and times; and, as such, it has changed considerably in the Western societies in the last, permissive decades.
It would now be good to continue the research on the visceral part of the brain.