Sex and the brain – the chemistry of love

Doctoral research
Contemporary Neuroscience: Sex and the Brain

The chemistry of love

Saybrook Graduate School and Research Center
San Francisco
July 2006

Sex therapists often say, “The biggest sex organ is the brain.” Is this true? And if so, what is meant by it? It takes more than brain chemistry for most humans to be satisfied with relationships and sexual activities. People can block or enhance instinctive and chemical sexual impulses and motivations.

Clients wonder why “chemistry” isn’t enough to keep them interested, or to provide depth and quality to their relations. As we will see, animal instinct is integral to sexual behavior in humans, and we have some understanding of what happens in the brain prior to, during, and after sexual activity. We will also see what we understand about where and how in the brain dwell the more complex emotional and cognitive components that make up the total picture of sex for humans.

Defining “sex” is in itself not a straightforward matter. In a workshop of ten adults whose purpose was to discuss the workings of sex and love, an entire six-hour segment was unexpectedly focused on defining “what is sex?” Seemingly more complex, ambiguous questions such as “what is ‘in-love’?” were handled in minutes, with consensus among the group (Orion, 2002).

In many religions the only acceptable expression of sex means intercourse, and in some cases, only for procreation, and not for pleasure. Many people also define “sex” for themselves as intercourse only, including President Clinton, apparently, whose denials and declarations added to the influence of a generation of adolescents who think that oral sex is not “real sex” since it is not intercourse. Within such a traditional and archaic cultural more, pleasure other than that experienced by the man during ejaculation is at least unnecessary and unimportant, and at worst, sinful. The only acceptable excuse for intercourse in this view is within marriage for the purpose of procreation: a religious dictate, not supported by scientific data.

The dictionary isn’t much help. “Sex” is defined as “…sexual activity, including specifically sexual intercourse…” (Webster’s). Additional Webster definitions refer only to the genital and biological differences between male and female and the origins of such terms in old English. As a verb, Webster’s states that “sex” means to “determine the sex of, as with chickens” or, quite a different interpretation, to “sex someone up – informal: to arouse someone’s sexual interest.” These illustrations represent two poles of biological and social influences on what “sex” means to humans. In exploring neuroscience, sex, and the brain, it is impossible not to call upon other sciences such as psychology, sociology, anthropology, and biology, all of which make clear that “sex” is far more complex and meaningful than even the best educated of the past centuries have known.

Touch and other SENSE-ual explorations are part of sexual activity as many people describe it. The importance of touch is supported by scientific data, which includes how touch influences brain activity. Many individuals don’t feel “in the mood” without first experiencing physical sensations that do not focus on genitals and are not what they consider “sex acts.” Dr. Michelle Weiner-Davis, sex therapist and author of several books on desire and marriage, explains (2003, p.29) that the human sexual response cycle, defined for the first time by Master’s and Johnson in the 1960’s, has recently been questioned by sexologists as a universal process. What has since the ‘60’s been considered standard is the progression of “[spontaneous emotional] desire > [physical] arousal > orgasm > resolution.” Now we know that many people do not consistently feel sexual desire spontaneously as a result of thoughts, emotions, related brain chemistry, or other involuntary stimuli. This at first led to the false conclusion that such individuals have low desire, or no desire for sexual activity. Recent studies have shown that these people do experience sexual desire, but they need deliberate sensual stimulation to initiate arousal first, which leads to chemically supported emotional desire. For these people, the cognitive, emotional, and chemical state of desire follows physical arousal, not the other way around as was originally thought. It has been considered normal for sexual desire to be catalyzed spontaneously by hormones and by chemicals in the brain as an instinctive function. Now it is known that it is also normal when sexual desire is not catalyzed automatically by instinctive drive, and does not always “just happen” to people. In the absence of spontaneous sexual desire, the human sexual response cycle can be initiated by conscious choice and deliberate physical arousal.

This experience can be explained by the chemistry of touch. It is well known among social and sexual scientists that most people report emotional connection as an important part of what makes sex satisfying. Touching is part of a chemical process that lifts mood and helps create emotional connection. Animal studies and babies who have been raised in an environment with minimal touching have taught us that many species fail to learn, love, thrive, and will even die, without the stimulation, comfort, and the chemicals released into the brain and body generated by touch.

Psychologist, speaker, and author Joan Borysenko, in a recently aired television lecture explained (2006) that touch both releases growth hormones that restore tissue, and stimulates the release of seratonin, which elevates mood. Dr. Weiner-Davis points out (2003, p. 33) that oxytocin is involved with touching. Oxytocin, she tells clients, is a “bonding hormone” that is involved between mothers and infants, is produced in the breast-feeding process, and is also released at orgasm. Getting these hormones and brain chemicals going therefore helps to “sex someone up” when they do not sex themselves up, automatically.

We know that touching can help spark interest in sexual activity. Neurobiological brain research provides a “touch map” of the brain. A diagram of this map shows that the entire cerebrum is wrapped up by the area of the cortex that registers touch on every part of the body. This wrapping includes the areas registering sensations of the genitalia; “the area given over to the genitals is about as large as the rest of the chest, abdomen, and back put together” (Carter, 1998, p. 75). It makes sense, then, that touching any area of the “map” could spread sensations that lead to genital arousal, and feelings of desire.

That brain chemistry is a major factor in sexual arousal and satisfaction is becoming common knowledge with the advent of erectile enhancing drugs such as “Viagra”, “Levitra”, and “Cialis”. A television commercial for “Cialis” asks the question, “When the time is right, will you be ready?” This 36-hour erectile enhancer, like similar drugs on the market, can enable the sexual functioning of the penis, i.e. physical arousal, but does not enhance the ongoing libido, or create emotional desire. It can be a physical catalyst to relieve the erection caused by the drug, but the brain and body must still allow and support sexual activity for people to report that they have experienced satisfying sex. The ad is asking, when the brain is ready, will the body be able to perform? Erectile enhancers can make sure of it. They do not, however, guarantee sexual satisfaction nor relationship success.

“Viagra”, the first and least sophisticated of this type of drug, is the most compelling physically. One client described it as “a sledgehammer to kill a fly.” Another described it as creating an almost involuntary necessity to fornicate. His genitals were strongly aroused “by surprise, all of a sudden,” which the couple experienced as a deterrent to the natural emotional flow they wanted of being together sexually (Orion, conversation with clients, 2006). Only 50% of men who were prescribed Viagra when it was introduced then reordered it, according to Michael Metz, Ph.D., a sex therapist specializing in men’s erectile issues (2003). The reason for this, he explains, is because sexual relations are more complex for humans than just being about genitals banging together until ejaculation occurs; a pill does not address social, emotional, or relationship issues.

The chemical brain functioning related to sexual activity is integral and core to the larger complex picture. Dopamine, endorphins, oxytocin, vasopressin are “drugs” that the brain and body produce. Unlike “Viagra”, they can cause emotional response where little or none existed before these chemicals were released. They can cause behaviors that may be bewildering in the lives of two lovers who are otherwise incompatible, for example. They don’t enjoy compatibility; they just have “chemistry,” the couple might explain. Why is sex called “making love”? Why does “casual sex” sometimes become much more? What do people want that erectile enhancers can’t deliver?

Helen Fisher, Ph.D., an anthropologist, carried out brain research at Rutgers University in 2002 with 40 people who claimed to be “madly in love.” Half of them were requited, the other half rejected in this emotion. MRI scans revealed that photos of the beloved (but not of friends or acquaintances) created significant activity in the right ventral tegmental area, from which dopamine cells are projected into other parts of the brain. Dr. Fisher explained as one example, “kissing sprays dopamine all over the brain.” In scientific terms this means that dopamine is projected into the posterial dorsal caudate and its tail, both instrumental in the brain’s reward and motivation system. The “highly wired” prefrontal cortex is also in the pathway of the dopamine, but the amygdala, which is associated with fear (and probably therefore caution) is temporarily quieted (McManamy, 2006, p. 1).

Dr. Fisher concludes from her studies that romantic love is part of the motivation and reward system of the brain. The brain links the drive to appropriate emotions in response to how the relationship is going. A person “in love” is constantly monitoring the situation, and the pre-frontal cortex is assembling data, recognizing or developing patterns, and choosing strategies of behavior.

In a lecture in San Francisco in 2004 (Open Heart, Open Mind Symposium, San Francisco) Dr. Fisher discussed the motivation and reward system of love in terms of evolution and survival. She developed a theory as to the reasons for this internal behavior. She considers it a three-step process – and asserts that there are three corresponding parts of love involving different brain systems, which she thinks developed to insure propagation of the species. First, humans scan the environment for suitable partners. Other studies also suggest that smell, thoughts, chemical responses, and visual markers help us choose possible partners from a field of many. Dr. Fisher calls this step lust, the craving for sexual satisfaction, which is driven by estrogen and androgens and motivates us to “get out there” and search for sex partners.

She posits that in step two, we narrow the field when touching and kissing cause initial arousal and connection, which she calls attraction, or romantic or passionate love (see above regarding the kissing-dopamine influence). This part of the process is characterized by euphoria when things are going well (but when going badly, people can experience mood swings, obsessive thinking and behaviors, and intense craving for the other person). High and low states of being in love are driven by high dopamine and norepenephrine levels, or low seratonin. Dr. Fisher accounts for this second step as a means to focus our attention on one person long enough for further attachment to take place. It’s when we carry the passionate behavior through to orgasm that resulting chemical reactions serve to bond the partners: they “fall in love” and are compelled to repeat the behavior in order to maintain their bond long enough for offspring to survive.

This becomes the third phase, which Dr. Fisher calls attachment. Attachment is characterized by a sense of calm, peace, and stability, a state which can be created by the chemical and hormonal influences of oxytocin and vasopressin, both results of orgasm, among other things. It is estimated that this process, which she considers an evolutionary one, assures that the team of parents will stick together long enough to provide nurture and protection for offspring. Contrary to our “Cinderella” ideal of happily ever after, the naturally induced attachment state often lasts only an average of two to three years.

This may explain the phenomenon that most people report of being “hot” in the beginning of the relationship, but anywhere from a few months to a few years later, “the honeymoon is over.” Dr Fisher noted that images of the brains of people who had been in love the longest were beginning to show signs of “the satiation response,” indicating that their drive for sexual, passionate satisfaction with that particular partner is waning. She believes this is a protection against “sexual exhaustion,” (McManamy, 2006, p.2). She noted, however, that attachment can remain or grow even when passionate love fades, because high levels of oxytocin and vasopressin present with attachment feelings can interfere with the rush of dopamine to the pathways of hot romantic love. This may explain why deliberately choosing activities and behaviors to stimulate the two passion neurotransmitters – a common prescription for low-sex marriages – may keep long term attached partners more sexually active.

Dr. Fisher also cautions us that these systems work together in the brain and body, so she advises, “Don’t copulate with people you don’t want to fall in love with, because you might do just that” (ibid, p. 1). She reiterates that testosterone can jumpstart the two love neurotransmitters and orgasm can create or support attachment hormones. This data provides answers to the questions of why the general public uses the term “making love,” and why unsuitable partners may attach themselves to one another with strong and possibly detrimental emotional and behavioral outcomes.

Dr. Fisher suggests that this three step process could indicate that “millions of years ago” humans may have had multiple partners, which also assured the greater probability of the survival of a particular set of male genes (2004).

Divorce statistics, among other data, show that a majority of humans still have multiple partners. Data from Dr. Fisher’s research and statistics from several fields support the idea that humans are not designed for lifelong and fundamentally monogamous relationships, and that we need to survive long term in groups rather than as isolated couples. Her thesis that all this human chemistry exists to propagate the species and ensure species survival does not explain same sex attraction and sexual activity that is common in many species in addition to humans. Reward-seeking functions are themselves basis for repeating activities that result in physical pleasure, as is simple common sense – if it feels good, do it. Her theory does not explain the observation that dozens of species repeatedly engage in a variety of sexual behaviors that result in orgasm and apparent affection, but do not involve mating for the purpose of impregnation.

At a 2004 conference of the Society for the Scientific Study of Sexuality, Joan Roughgarden, Ph.D., discussed findings published in her recent book Evolution’s Rainbow. Her book and lecture outline her social biological research that identified sixty species (adding to thirty already documented) which display behaviors contrary to proscribed “moral” beliefs of several human societies. Included in the study were apes, our closest animal relatives, who engaged on a regular basis in sex for pleasure, including with same sex partners. A significant number of species contained a member who could be described as transgendered – with physical parts and roles in the community of both sexes. Contrary to human behavior in some cultures of treating such individuals as outcasts, the transgendered members of other species are valued because they serve vital purposes in the group as peacemakers, matchmakers, or problem solvers.

Dr. Roughgarden (2004) points out that in evolutionary terms, behaviors, diseases, or abnormalities that are determined a threat to survival of the species occur less than one percent of the time before being wiped out in a few generations – or the species does not survive. Homosexual and sexual pleasuring behaviors are commonplace among the numerous species studied – and, despite moral indignation, also among humans – and therefore cannot be classified as sicknesses or abnormalities.

While social and biological science support the natural predisposition of some humans to be bi-sexual and homosexual, human societies are such that more “proof” is needed to combat prejudice. In recent decades technological advances in brain neuroscience have produced data to help answer the question, “Is there a ‘gay brain’?” In the text Mapping the Mind (1998) Rita Carter outlines research publicized in 1991 revealing that the brains of a group of homosexual men who had died from AIDS were structurally different from brains of heterosexual men. A significant part of the hypothalamus that triggers typical animal male behavior was much smaller in the homosexual group and also resembled the corresponding brain area in women. A subsequent study supported the theory of brain differences; the corpus collosum in gay men was discovered to be bigger than in heterosexuals. Three years later research done by molecular biologist Dean Hamer of the National Institute of Health in Washington D.C., suggested that a specific matrilineal gene influenced sexual orientation in men (p. 71). While more information can clearly be useful to create irrefutable conclusions, these landmark studies provide strong evidence that there are specific biological roots to homosexuality – evidence that has long existed in studies of history, anthropology, and social sciences.

So when people say, “…if the chemistry between us is right,” or “the chemistry just wasn’t there…” Helen Fisher’s interpretation might be that one individual doesn’t “see” the other as a potentially good childbearing mate. Other studies also support the theory that humans are attracted to one another because they set off mutual brain chemistry and are perceived biologically as the mate most likely to succeed at carrying forth the gene pool. One such recent study in the United Kingdom was aired on the Discovery Channel (2006). Men and women were individually asked to “design” with computer images the ideal person of the opposite sex to whom they would be attracted. While there was certainly variation in features including hip and breast size, this and other studies have shown that a majority of men are attracted to women who have wide hips in proportion to their waist, apparently a figure good for child bearing, and large breasts, purportedly because they are good for nurturing infants. Women are often attracted to taller men with larger torsos and certain features that, it is presumed, indicate strength and resourcefulness, as these men are instinctively perceived as more likely to be adequate protectors and providers for a nursing mother and baby. Other species as well weed out community members who are not strong, agile, and well endowed.

These theories and data make sense, when we are discussing sexual attraction for the purpose of procreation and creating a family unit. Other theories must be additionally employed if we are to provide answers as to why people are attracted to persons of their own sex, why people (and other animals) seek sex purely for pleasure, or why some people make matches that are entirely unsafe or unlikely to succeed in a family partnership situation. Including those discussed in this paper, several schools in social science have theories and data applied to these phenomena; how much and in what ways these questions can be answered by brain science is still subject of study.

Studying sex and the human brain is difficult for reasons besides the obvious issues of privacy and ethics. The most advanced technology for brain imaging requires absolute stillness of the head, which is also covered with electrodes. Or the subject is contained in a “clanging metal cigar tube” (MRI) with a rubber clamp in the mouth (Carter, 1998) – hardly natural circumstances for studying human sexual behavior. Much of “why” and “who” can be surmised and correlated from data compiled by several fields; brain science can provide limited explanation as to “how” basic animal sexual impulses are filtered through more complex thoughts, memories, feelings, and social programming. Indeed our brains have a built-in regulation system that inhibits motivational survival behaviors, or we might constantly eat or have sex. In addition we curb our various appetites by filtering instinctive behaviors through the lobes of the frontal cortex, considered the seat of construction for abstract ideas and what have been termed “morals” in the text Mapping the Mind (p. 74).

According to the author of that text, Rita Carter, neurobiological science maps out sex drive as part of survival motivation based in the hypothalamus (as it is in many animals). Sexologists concur with Carter, however, that human sex drive is not a simple brain process. Carter explains that (p. 72) while human sex drive centers on the hypothalamus, “…like other urges, it radiates out to encompass a wide range of other brain areas in both the limbic [system] and the cortex.” She continues that sex drive and sexual activity are split into various elements, which localize themselves and that “…the clumps of tissue that produce each aspect of sexual feeling and behavior are activated by various neurotransmitters in conjunction with sex hormones.” Theories of other scientists and practitioners are supported by this “map” described by Carter, which also reveals that an “urge-reward-relief” system operates the sex drive as well as other basic urges. “Sexual drive is created by excitatory neurotransmitters; the intense ‘reward’ of orgasm is caused by a massive rush of dopamine; and the feeling of relaxation that follows is due to a hormone called oxytocin” (p. 42).

Glimpses into the nature of human complexity have outdated such issues as nature vs. nurture, biology vs. social influence. The brain clearly has a two-way street with regard to sexual functioning. Humans are always “warmed up and ready for sex” according to Carter, as both the limbic system and the environment are providing sexual impulses and information from two different directions of the brain at all times. “Other species show this degree of interest only when the female is ready to conceive.” Because of this continuous state of readiness, humans have created a complex system of dealing with sex and relationships involving many kinds of brain activity: romantic love, considered in brain science as a high level cognitive activity; visual and physical recognition; emotions; and straightforward body function (p. 74).

This complexity distinguishes humans from the rest of the animal world, as does constant sexual availability. The drawback is that faults occurring anywhere along the line of such a complex system in any part of the brain may result in some type of sexual or other dysfunction. As medical discoveries concerning trauma have shown, damage to certain parts of the brain can result in bazaar or extreme sexual behaviors; these discoveries reveal the seat of impulses or regulations in areas of the brain to include the right frontal cortex and the temporal lobe. Involuntary sexual sensations and movements have resulted from epileptic seizures centering in the junction of the frontal and parietal lobes where lie the sensory and motor cortices.

Kathryn Hall, Ph.D., states (2004), “Sexual desire is…complex and requires our thoughts, our emotions, and our bodies to work in sync” (p. 19). One of the most common complaints presented to sex therapists is traditionally labeled by clinicians as “low desire.” Both women and men can experience a frequent and persistent lack of desire for sex, called “hypoactive sex drive” in the DSMIV. According to Michelle Weiner-Davis (2003) more women experience this – as much as 50% of women, while 20% of men complain of the condition (p. 23). Often couples enter therapy because one partner is far more interested in sex than the other, each misunderstanding the great contrast in the feelings of the spouse.

An unfortunately popular self-help book of the recent decade, Men Are from Mars, Women Are from Venus, by John Gray, purports to outline the contrasts between the sexes with the idea that doing so will be helpful. Dr. Marty Klein, author, sex therapist, and speaker (2004) assures listeners and clients that there are far more similarities between men and women, and suggests that building upon these is an effective strategy for bringing people together (Lecture, San Francisco). Certainly there are noticeable differences between men and women physically; many other variations in characteristics are clearly attributed to socialization.

Are the brains of women significantly different from those of men? According to Carter in Mapping the Mind, there are structural differences that have been documented. An area full of cells that are more sensitive to androgens (male hormones) is larger in men, known as the hypothalamic nucleus (the area found to be dramatically smaller in gay men). Some studies have also found that this area is larger in some women than others and may correlate with smaller breast size, hirsutism, lower voice, and more aggressive behavior, all considered male-typical sexual characteristics. These behaviors and related tendencies have been labeled “male-typical” because they are observed consistently and significantly more in male rather than female humans, and other animals. There are also female-typical sexual characteristics, considered such for the same reason (p. 73).

Another major structural difference between the male and female brain is the connection between the right and left hemispheres. This connection is relatively larger in women than in men, as is a more primitive link between the unconscious areas of the hemispheres, the anterior commissure. Since the “right brain” is known to be more sensitive to emotions and creativity, the observation that women are generally more sensitive than men may have physical cause, as the connection between the hemispheres allows for more and easier passing of information to the left side, which can then process and utilize the emotional and creative information (ibid).

As men and women age, they each tend to lose tissue in different parts of the brain. Women tend to have potentially more memory and spatial problems, and men more personality and emotional changes. Men also tend to lose more of their brain tissue, and to do so at an earlier age.

Women and men use their brains differently as well, imaging studies show (1998, Carter). Women tend to bring both halves of the brain to task when faced with complex mental tasks, whereas men tend to use only the side that they perceive to be suited to the problem. Some describe women as having a broader view of life for this reason, or men as being focused more narrowly, thereby achieving different results than a woman (p. 73). I question to what extent these differences in brain use result from generations of social programming about roles that men and women fulfill – about how men are from Mars, and women are from Venus – why baby boys are dressed in blue and are given footballs, and baby girls are dressed in pink and are given dolls.

Variations between genders in sexual brain functioning do exist and are caused by hormones; these differences can be modified by behavior and environmental factors, according to information in Mapping the Mind. The underlying layout is predetermined in the womb by genes, however, and has associated behaviors distinct and consistent enough to accurately be labeled as male-typical and female-typical, as previously stated. Males are typically hard-wired to be more assertive and take a penetrative role, females to be more contemplative and receptive.

Some women claim to eat more, or reach for “comfort foods” when they are in distress over relationships – or lack thereof. This may have brain chemistry behind it – as female-typical sex behavior is located in the ventromedial nucleus of the hypothalamus, the same nucleus that plays a crucial part in hunger. Conversely, the nucleal area that plays such a role in male-typical sex behavior is associated with aggression.

So, male behavior is associated with hardiness of drive. Female sex hormones direct the type of sexual behavior displayed, but they do not have much influence on the strength of the sex drive. No wonder then that a greater number of women complain of “lesser desire” nor that some develop desire when certain types of sensual experiences help them do so. Overall the sex drives in men and women are controlled by the actions of testosterone and adrenaline. It is clear that “sex drive” is brought about and sexual behavior is influenced by the interaction of many brain areas, chemicals, and functions. The brain is the largest sex organ, when we understand sexual satisfaction as an integrated experience of brain/body chemistry, consciously chosen behaviors, and social influences on our actions, thoughts, and feelings about sex.

Supporting this conclusion is the most recent study of women and sex, which arrived in book form at my door as I was completing this paper. The Heart and Soul of Sex, by Gina Ogden, Ph.D., contains the results of brain scan studies (p. 124) that show twelve active areas of the brain during sexual activity and orgasm. One of these is the temporal lobe, which is important in hearing, and also attributed to activity relating to spiritual experiences or religious ecstasy. Reports by women in the study confirm that the kind of sexual experience that humans seek is much more than a genital experience. Ogden states: “[this study also showed] that women’s vaginal-cervical stimulation and orgasm activated multiple regions of the brain – and activated them simultaneously…these laboratory findings represent a major breakthrough in sex research. They provide the first truly objective data to support the idea that response to physical stimulation invokes much more than physical sensation – it may also invoke thoughts, fears, joy, surprise, memories, dreams, pain, pain relief, religious ecstasy, discernment, and anticipation of reward and punishment. Moreover, it shows that all of these occur whether or not we’re consciously aware that all of them are happening.”

As a conclusion to this paper on sex and the brain, Ogden’s data shows how the brain is the biggest sex organ, and why “sex” is much more than intercourse for humans. Fisher’s research may correlate with evolutionary instinct for propagation and survival of the species; other brain research shows that humans clearly have many brain, mind, and body processes involved with sexuality beyond the drive to procreate. I submit that individuals who complain of “low” desire, are actually suffering from lack of awareness and utilization of the entire spectrum of possible experience that this recent research shows we are hardwired to attain. This data may be a catalyst for understanding how more people can learn to connect with what some of the women in the Ogden study call “sacred sex.”

REFERENCES

Borysenko, Joan, 2006. Inner Peace for Busy People. Lecture, aired 7-10 -06: LIME T.V.

Carter, Rita, 1998. Mapping the Mind. London: University of California Press with Weidenfeld & Nicolson.

Discovery Channel, 2006. Real Sex.

Fisher, Helen, 2004. Lecture: Why we love. San Francisco: Open Mind, Open Heart Sexuality Symposium.

Hall, Kathryn, 2004. Reclaiming your sexual self. Hoboken, NJ: John Wiley & Sons, Inc.

Klein, Marty, 2004. Everyone’s from Earth, lecture. San Francisco: Open Mind, Open Heart Sexuality Symposium.

McManamy, John, 2004. The brain in love and lust: article, http//www.mcmanweb.com/love_lust.htm. Dowloaded 7/13/2006.

Metz, Michael, 2003. Coping with premature ejaculation. Lecture, San Anotnio, TX: Annual Conference of the Society of the Scientific Study of Sexuality.

Ogden, Gina, 2006. The Heart and Soul of Sex. Boston: Trumpeter Books.

Orion, Rhea, 2002. People’s experience of sex, Peer Day workshop. Montpelier, Vermont: Union Institute & University.

Roughgarden, Joan, 2004. Evolution’s Rainbow. Berkeley & Los Angeles, California: University of California Press.

Roughgarden, Joan, 2004. Darwin & Gender Diversity. Plenary presentation, San Francisco: Western Regional Conference of the Society for the Scientific Study of Sexuality.

Weiner-Davis, Michelle, 2003. The Sex Starved Marriage. New York: Simon & Schuster.

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One thought on “Sex and the brain – the chemistry of love

  1. The Brain chemistry is the major factor in sexual arousal and it is completed by the following manner.(1) Appearance of the opposit sex(2) Aroma of the body. When a man seeing his partner, the brain makes some video picture about the parts of the body and structure, that influences for sex, and Aroma (fragrance) of the body penetrates to the brain, it also makes some chemical reaction on the brain for tendency of sexual action. I think Eye and Nose are the mediaters to coax the Brain for sexual desire.

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