Neuroscientists have devoted great efforts to answer the basic questions about eating, drinking, breathing and moving; they have also been striving to understand how we perceive, think, sleep and remember.

But what about sex? Taboos in many cultures, moral censorship and the immaturity of the social, psychological and physiological sciences in these fields have impeded for a long time research concerning human sexual behaviour. It was only with the pioneering studies of sexologists Havellock Ellis and Alfred Kinsey, in the first half of this century, and later, of physiologists William Masters and Virginia Johnson, that an objective study of human sexual response began to be unraveled.

Today, we find many studies concerning the embryological, genetic and biological aspects of the reproductive apparatus, such as the spermatozoa and ova, fertilization, development and birth, as well as the anatomy of the genital tracts in both sexes. We also find a lot of information about the anthropological, social and cultural aspects of sexual behavior. However, the literature describes very few studies on the physiology of the human sexuality and how the brain organizes the sexual behavior.

The human sexuality is closely related to reproductive behavior in terms of propagation and the survival of the species as well their neural and physiological mechanisms. However, sexuality not always results in reproduction because it is a motivated behavior. The success in completing the sexual act depends on local excitation and psychic stimulus.

Other behaviors are also motivated, such as the feeding behavior. However, the difference between the sexual motivation and these primary drives is emphasized when satiation is considered. When a hungry or thirsty animal ingests a sufficient quantity of food or water, the restoration of the energy or fluid balance of the organism returns it to a state of homeostatic balance. Sexual activity depletes the organism's energy stores; the sex drive is satiated only when fatigue and exaustion override it and it recurs when the body has replenished its energy stores. Additional important differences arise because sexual motivation is largely elicited by environmental cues, whereas hunger and thirst reflect internal changes which stimulate interoceptors.

Sexual behavior, arousal, and motivation occur only in special environmental situations which provide particular types of sensory stimulation. No amount of stimulation will arouse sexual motivation and behavior unless the organism is physically ready to mate. This physiological readiness to respond selectively to sexual stimuli is provided by hormonal changes which affect neural as non-neural mechanisms throughout the body.

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.

Physiological Basis of Coitus

Swelling and Lubrication's Process in Woman The Erection's Process in Man Phases of Excitation Female Orgasm Pills for Orgasm in Woman Male Orgasm

Neural Basis of Coitus

Role of Hormones in Human Sexuality Nervous System and Its Involvement with Sexual Behavior How the Nervous System Works During Sexual Intercourse ?

Author: Dr. Silvia Helena Cardoso, PhD. Psychobiologist, master and doctor in Sciences by the University of São Paulo and post doctoral fellowship by the University of California, Los Angeles. Invited Professor and Associate Researcher of the Center for Biomedical Informatics, State University of Campinas (Unicamp), Brazil.
Correspondence