How does visual sexual arousal work between the eyes, brain, and genitals/gonads?

How does visual sexual arousal work between the eyes, brain, and genitals/gonads?

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When many people look at sexual images, they often can become sexually aroused, including full genital arousal, and feel urges, known more often used as "horny" as slang/urban usage.

How does this process work in males and females? Is it different in males than in females, or is the network the same between the eyes and the brain, down to the genitals as a precursor to masturbation, sex, etc.? Also, what exactly happens in the brain before it tells the genitals to get horny or such? Examples would be in viewing porn, naughty images/pics, etc.

Men and women and girls and boys alike can get full arousal from this. How does the process work?

Sexual arousal is a very complex response, that includes a whole range of physiological changes, firing of lots of neural pathways, increased muscle tension, elevated heart rate with increased blood flow to the skin, primary and secondary sexual organs and a whole lot of hormonal spikes.

Sexual desire is defined as the behavioural drive that motivates individuals to fantasize about or seek out sexual activity. In contrast, sexual arousal is defined as the autonomic physiological processes that prepare the body for sexual activity (Toledano, Pfaus., 2006).

The brain is rightfully regarded as the largest sexual organ, with most of the pleasure arising from the limbic system of the brain (which interestingly enough, is common to all mammals regulating emotion and encouraging the avoidance of painful of aversive stimuli and the repetition of pleasurable experiences).

From a physiological perspective sexual arousal is controlled by the parasympathetic portion of the autonomic nervous system and manifests itself as vasodilation in sexual organs along with several other physiological phenomena including an increase in heart rate. An orgasm and in particular male ejaculation is controlled by the sympathetic portion, this is also accompanied by deactivation of many areas in the brain relating to external stimuli in particular fear, allowing the mind to focus on the task at hand.

Now it is a bit long to go into the details of the sexual response cycle, and hence here is a brief summary:

Neural pathways:

Prior to the physical stimulation, comes sexual desire. Largely mediated by emotion through the limbic system, activation of the amygdala can trigger penile erection, sexual feelings,(Georgiadis and Holstege, 2005) sensations of extreme pleasure (Olds and Milner, 1954), memories of sexual intercourse (Gloor, 1986), as well as ovulation, uterine contractions, and orgasm.

The amygdala is sexually differentiated part of the brain that is known to produce sex specific responses. In short the amygdala has a pathway (amygdalofugal pathway) that connects with the major regions of the brain that regulates sexual feelings. An increased density of enkephalins and opiate receptors can be also found in amydala, which induces extreme feelings of pleasure.


Males more then females, were found to have greater amygdala activation when presented with a sexually pleasing, visual stimuli (Hamann et al., 2004).

Moving on, other areas of the brain implicated in sexual arousal are…

Input travels from the basolateral nuclei of the amygdala along the amygdalofugal pathway to the ventral striatum, made up of the nucleus accumbens, putamen and parts of the caudate nucleus. The nucleus accumbens plays a role in pleasure and reward due to a large large of dopaminergic neurons from the VTA (ventral tegmental area).

The Vagus nerve is known to lead to the Nucleus Tractus Solitarii (NTS) in the Medulla Oblongata. Following this stimulation of the brain via the vagus nerve during orgasm there was a difference in activity between preorgasm and orgasm. Areas of activation during and after orgasm include the hypothalamic paraventricular nucleus (PVN), midbrain central gray, amygdala, hippocampus, anterior cingulate, frontal, parietal, temporal and insular cortices, anterior basal ganglia, and cerebellum (Whipple, 2008). Although this may be the explanation for female orgasms, there is no evidence to suggest that this is the case for males.

Hormonal changes: I am not going to write too much about this as this information is readily accessible in the net. Sexual arousal causes the cerebral cortex to signal the hypothalamus to stimulate the production of testosterone, the production is regulated by a complex chain of events known as the hypothalamic-pituitary-gonadal axis, which ultimately causes the pitutary gland to release luteinizing hormone which signals the testes to produce testosterone and ovaries to produce oestrogen.

You can read more here:

For an in-depth analysis I recommend this book: Greenberg, Jerrold S., Clint E. Bruess, and Sara B. Oswalt. Exploring the dimensions of human sexuality. Jones & Bartlett Publishers, 2014.

This is a good review for endocrinology in sexual arousal: Bancroft, J. "The endocrinology of sexual arousal." Journal of Endocrinology 186.3 (2005): 411-427.

As usual, wikipedia also covers a few models of sexual arousal (Singer, Basson's etc… ) that I have not mentioned here:

Your Guide to the Sexual Response Cycle

The sexual response cycle refers to the sequence of physical and emotional changes that occur as a person becomes sexually aroused and participates in sexually stimulating activities, including intercourse and masturbation. Knowing how your body responds during each phase of the cycle can enhance your relationship and help you pinpoint the cause of any sexual problems.

What Are the Phases of the Sexual Response Cycle?

Sexual Response Cycle

The sexual response cycle has four phases: excitement, plateau, orgasm, and resolution. Both men and women experience these phases, although the timing usually is different. For example, it is unlikely that both partners will reach orgasm at the same time. In addition, the intensity of the response and the time spent in each phase varies from person to person. Understanding these differences may help partners better understand one another's bodies and responses, and enhance the sexual experience.

Phase 1: Excitement

General characteristics of the excitement phase, which can last from a few minutes to several hours, include the following:

  • Muscle tension increases.
  • Heart rate quickens and breathing is accelerated.
  • Skin may become flushed (blotches of redness appear on the chest and back).
  • Nipples become hardened or erect.
  • Blood flow to the genitals increases, resulting in swelling of the woman's clitoris and labia minora (inner lips), and erection of the man's penis.
  • Vaginal lubrication begins.
  • The woman's breasts become fuller and the vaginal walls begin to swell.
  • The man's testicles swell, his scrotum tightens, and he begins secreting a lubricating liquid.

Phase 2: Plateau

General characteristics of the plateau phase, which extends to the brink of orgasm, include the following:

  • The changes begun in phase 1 are intensified.
  • The vagina continues to swell from increased blood flow, and the vaginal walls turn a dark purple.
  • The woman's clitoris becomes highly sensitive (may even be painful to touch) and retracts under the clitoral hood to avoid direct stimulation from the penis.
  • The man's testicles are withdrawn up into the scrotum.
  • Breathing, heart rate, and blood pressure continue to increase. may begin in the feet, face, and hands.
  • Muscle tension increases.

Phase 3: Orgasm

The orgasm is the climax of the sexual response cycle. It is the shortest of the phases and generally lasts only a few seconds. General characteristics of this phase include the following:

  • Involuntary muscle contractions begin.
  • Blood pressure, heart rate, and breathing are at their highest rates, with a rapid intake of oxygen.
  • Muscles in the feet spasm.
  • There is a sudden, forceful release of sexual tension.
  • In women, the muscles of the vagina contract. The uterus also undergoes rhythmic contractions.
  • In men, rhythmic contractions of the muscles at the base of the penis result in the ejaculation of semen.
  • A rash, or "sex flush" may appear over the entire body.


Phase 4: Resolution

During resolution, the body slowly returns to its normal level of functioning, and swelled and erect body parts return to their previous size and color. This phase is marked by a general sense of well-being, enhanced intimacy and, often, fatigue. Some women are capable of a rapid return to the orgasm phase with further sexual stimulation and may experience multiple orgasms. Men need recovery time after orgasm, called a refractory period, during which they cannot reach orgasm again. The duration of the refractory period varies among men and usually lengthens with advancing age.

Discovery Health.
Reviewed by Robert S. Phillips, MD on July 08, 2008
Portions of this page © Cleveland Clinic 2008


Doctoral research
Contemporary Neuroscience: Sex and the Brain

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.”

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There are several informalities, terms and phrases to describe sexual arousal including horny, [1] turned on, randy, steamy, and lustful. [2] Things that precipitate human sexual arousal are called erotic stimuli and colloquially known as turn-ons.

Depending on the situation, a person can be sexually aroused by a variety of factors, both physical and mental. A person may be sexually aroused by another person or by particular aspects of that person, or by a non-human object. The physical stimulation of an erogenous zone or acts of foreplay can result in arousal, especially if it is accompanied with the anticipation of imminent sexual activity. Sexual arousal may be assisted by a romantic setting, music or other soothing situation. The potential stimuli for sexual arousal vary from person to person, and from one time to another, as does the level of arousal.

Stimuli can be classified according to the sense involved: somatosensory (touch), visual, and olfactory (scent). Auditory stimuli are also possible, though they are generally considered secondary in role to the other three. [ citation needed ] Erotic stimuli which can result in sexual arousal can include conversation, reading, films or images, or a smell or setting, any of which can generate erotic thoughts and memories in a person. Given the right context, these may lead to the person desiring physical contact, including kissing, cuddling, and petting of an erogenous zone. This may in turn make the person desire direct sexual stimulation of the breasts, nipples, buttocks and/or genitals, and further sexual activity.

Erotic stimuli may originate from a source unrelated to the object of subsequent sexual interest. For example, many people may find nudity, erotica or pornography sexually arousing. [3] This may generate a general sexual interest that is satisfied by sexual activity. When sexual arousal is achieved by or dependent on the use of objects, it is referred to as sexual fetishism, or in some instances a paraphilia.

There is a common belief that women need more time to achieve arousal. However, recent scientific research has shown that there is no considerable difference for the time men and women require to become fully aroused. Scientists from McGill University Health Centre in Montreal (in Canada) used the method of thermal imaging to record baseline temperature change in genital area to define the time necessary for sexual arousal. Researchers studied the time required for an individual to reach the peak of sexual arousal while watching sexually explicit movies or pictures and came to the conclusion that on average women and men took almost the same time for sexual arousal — around 10 minutes. [4] The time needed for foreplay is strongly individual and varies from one occasion to the next depending on circumstances. [4]

Unlike many other animals, humans do not have a mating season, and both sexes are potentially capable of sexual arousal throughout the year.

Sexual arousal for most people is a positive experience and an aspect of their sexuality, and is often sought. A person can normally control how they will respond to arousal. They will normally know what things or situations are potentially stimulating, and may at their leisure decide to either create or avoid these situations. Similarly, a person's sexual partner will normally also know his or her partner's erotic stimuli and turn-offs. Some people feel embarrassed by sexual arousal and some are sexually inhibited. Some people do not feel aroused on every occasion that they are exposed to erotic stimuli, nor act in a sexual way on every arousal. A person can take an active part in a sexual activity without sexual arousal. These situations are considered normal, but depend on the maturity, age, culture and other factors influencing the person.

However, when a person fails to be aroused in a situation that would normally produce arousal and the lack of arousal is persistent, it may be due to a sexual arousal disorder or hypoactive sexual desire disorder. There are many reasons why a person fails to be aroused, including a mental disorder, such as depression, drug use, or a medical or physical condition. The lack of sexual arousal may be due to a general lack of sexual desire or due to a lack of sexual desire for the current partner. A person may always have had no or low sexual desire or the lack of desire may have been acquired during the person's life. There are also complex philosophical and psychological issues surrounding sexuality. Attitudes towards life, death, childbirth, one's parents, friends, family, contemporary society, the human race in general, and particularly one's place in the world play a substantive role in determining how a person will respond in any given sexual situation.

On the other hand, a person may be hypersexual, which is a desire to engage in sexual activities considered abnormally high in relation to normal development or culture, or suffering from a persistent genital arousal disorder, which is a spontaneous, persistent, and uncontrollable arousal, and the physiological changes associated with arousal.

Physiological responses Edit

Sexual arousal causes various physical responses, most significantly in the sex organs (genital organs). Sexual arousal for a man is usually indicated by the swelling and erection of the penis when blood fills the corpus cavernosum. This is usually the most prominent and reliable sign of sexual arousal in males. In a woman, sexual arousal leads to increased blood flow to the clitoris and vulva, as well as vaginal transudation - the seeping of moisture through the vaginal walls which serves as lubrication.

Female Edit

The beginnings of sexual arousal in a woman's body is usually marked by vaginal lubrication (wetness though this can occur without arousal due to infection or cervical mucus production around ovulation), swelling and engorgement of the external genitals, and internal lengthening and enlargement of the vagina. [5] There have been studies to find the degree of correlation between these physiological responses and the woman's subjective sensation of being sexually aroused: the findings usually are that in some cases there is a high correlation, while in others, it is surprisingly low. [6]

Further stimulation can lead to further vaginal wetness and further engorgement and swelling of the clitoris and the labia, along with increased redness or darkening of the skin in these areas as blood flow increases. Further changes to the internal organs also occur including to the internal shape of the vagina and to the position of the uterus within the pelvis. [5] Other changes include an increase in heart rate as well as in blood pressure, feeling hot and flushed and perhaps experiencing tremors. [7] A sex flush may extend over the chest and upper body.

If sexual stimulation continues, then sexual arousal may peak into orgasm. After orgasm, some women do not want any further stimulation and the sexual arousal quickly dissipates. Suggestions have been published for continuing the sexual excitement and moving from one orgasm into further stimulation and maintaining or regaining a state of sexual arousal that can lead to second and subsequent orgasms. [8] Some women have experienced such multiple orgasms quite spontaneously.

While young women may become sexually aroused quite easily, and reach orgasm relatively quickly with the right stimulation in the right circumstances, there are physical and psychological changes to women's sexual arousal and responses as they age. Older women produce less vaginal lubrication and studies have investigated changes to degrees of satisfaction, frequency of sexual activity, to desire, sexual thoughts and fantasies, sexual arousal, beliefs about and attitudes to sex, pain, and the ability to reach orgasm in women in their 40s and after menopause. Other factors have also been studied including socio-demographic variables, health, psychological variables, partner variables such as their partner's health or sexual problems, and lifestyle variables. It appears that these other factors often have a greater impact on women's sexual functioning than their menopausal status. It is therefore seen as important always to understand the "context of women's lives" when studying their sexuality. [9]

Reduced estrogen levels may be associated with increased vaginal dryness and less clitoral erection when aroused, but are not directly related to other aspects of sexual interest or arousal. In older women, decreased pelvic muscle tone may mean that it takes longer for arousal to lead to orgasm, may diminish the intensity of orgasms, and then cause more rapid resolution. The uterus typically contracts during orgasm and, with advancing age, those contractions may actually become painful. [9]

Male Edit

It is normal to correlate the erection of the penis with male sexual arousal. Physical or psychological stimulation, or both, leads to vasodilation and the increased blood flow engorges the three spongy areas that run along the length of the penis (the two corpora cavernosa and the corpus spongiosum). The penis grows enlarged and firm, the skin of the scrotum is pulled tighter, and the testes are pulled up against the body. [10] However, the relationship between erection and arousal is not one-to-one. After their mid-forties, some men report that they do not always have an erection when they are sexually aroused. [11] Equally, a male erection can occur during sleep (nocturnal penile tumescence) without conscious sexual arousal or due to mechanical stimulation (e.g. rubbing against the bed sheet) alone. A young man — or one with a strong libido — may experience enough sexual arousal for an erection to result from a passing thought, or just the sight of a passerby. Once erect, his penis may gain enough stimulation from contact with the inside of his clothing to maintain and encourage it for some time. [12]

As sexual arousal and stimulation continues, it is likely that the glans or head of the erect penis will swell wider and, as the genitals become further engorged with blood, their color deepens and the testicles can grow up to 50% larger. As the testicles continue to rise, a feeling of warmth may develop around them and the perineum. With further sexual stimulation, their heart rate increases, blood pressure rises and breathing becomes quicker. [10] The increase in blood flow in the genital and other regions may lead to a sex flush in some men. [13]

As sexual stimulation continues, orgasm begins, when the muscles of the pelvic floor, the vas deferens (between the testicles and the prostate), the seminal vesicles and the prostate gland itself may begin to contract in a way that forces sperm and semen into the urethra inside the penis. Once this has started, it is likely that the man will continue to ejaculate and orgasm fully, with or without further stimulation.

Equally, if sexual stimulation stops before orgasm, the physical effects of the stimulation, including the vasocongestion, will subside in a short time. Repeated or prolonged stimulation without orgasm and ejaculation can lead to discomfort in the testes (corresponding to the slang term "blue balls" [14] ).

After orgasm and ejaculation, men usually experience a refractory period characterized by loss of their erection, a subsidence in any sex flush, less interest in sexual activity, and a feeling of relaxation that can be attributed to the neurohormones oxytocin and prolactin. [15] The intensity and duration of the refractory period can be very short in a highly aroused young man in a highly arousing situation, perhaps without even a noticeable loss of erection. It can be as long as a few hours or days in middle-aged and older men. [10]

Psychological responses Edit

Psychological sexual arousal involves appraisal and evaluation of a stimulus, categorization of a stimulus as sexual, and an affective response. [16] The combination of cognitive and physiological states elicits psychological sexual arousal. [16] [17] Some suggest that psychological sexual arousal results from an interaction of cognitive and experiential factors, such as affective state, previous experience, and current social context. [18]

Female Edit

Research suggests that cognitive factors like sexual motivation, perceived gender role expectations, and sexual attitudes play important roles in women's self-reported levels of sexual arousal. [18] In her alternative model of sexual response, Basson [19] [20] suggests that women's need for intimacy prompts them to engage with sexual stimuli, which leads to an experience of sexual desire and psychological sexual arousal. Psychological sexual arousal also has an effect on physiological mechanisms Goldey and van Anders [21] showed that sexual cognitions impact hormone levels in women, such that sexual thoughts result in a rapid increase in testosterone in women who were not using hormonal contraception. In terms of brain activation, researchers have suggested that amygdala responses are not solely determined by level of self-reported sexual arousal Hamann and colleagues [22] found that women self-reported higher sexual arousal than men, but experienced lower levels of amygdala responses.

Male Edit

The relationship between sexual desire and arousal in men is complex, with a wide range of factors increasing or decreasing sexual arousal. [23] Physiological responses, such as heart rate, blood pressure, and erection, are often discordant with self-reported subjective perceptions of arousal. [24] This inconsistency suggests that psychological or cognitive aspects also have a strong effect on sexual arousal. The cognitive aspects of sexual arousal in men are not completely known, but the state does involve the appraisal and evaluation of the stimulus, categorization of the stimulus as sexual, and an affective response. [25] Research suggests that cognitive factors, such as sexual motivation, perceived gender role expectations, and sexual attitudes, contribute to sex differences observed in subjective sexual arousal. Specifically, while watching heterosexual erotic videos, men are more influenced by the sex of the actors portrayed in the stimulus, and men may be more likely than women to objectify the actors. [26] [27] There are reported differences in brain activation to sexual stimuli, with men showing higher levels of amygdala and hypothalamic responses than women. This suggests the amygdala plays a critical role in the processing of sexually arousing visual stimuli in men. [22]

Human sexual response cycle Edit

During the late 1950s and early 1960s, William H. Masters and Virginia E. Johnson conducted multiple studies into human sexuality. In 1966, they published Human Sexual Response, detailing four stages of physiological changes in humans during sexual stimulation: excitement, plateau, orgasm, and resolution. [28]

Singer's model of sexual arousal Edit

Barry Singer presented a model of the process of sexual arousal in 1984, in which he conceptualized human sexual response to be composed of three independent but generally sequential components. The first stage, aesthetic response, is an emotional reaction to noticing an attractive face or figure. This emotional reaction produces an increase in attention toward the object of attraction, typically involving head and eye movements toward the attractive object. The second stage, approach response, progresses from the first and involves bodily movements towards the object. The final genital response stage recognizes that with both attention and closer proximity, physical reactions result in genital tumescence. Singer also stated that there is an array of other autonomic responses, but acknowledges that the research literature suggests that the genital response is the most reliable and convenient to measure in males. [29]

Basson's sexual response cycle Edit

In 2000, Rosemary Basson presented an alternative model to the human sexual response cycle that is specific to women’s sexual response. [30] She argues that gender differences in sex drive, sexual motivation, sexual concordance, and capacity for orgasm underlie the need for an alternative model of sexual response. While the human sexual response cycle begins with desire, followed by arousal, orgasm, and finally resolution, Basson's [20] alternative model is circular and begins with women feeling a need for intimacy, which leads her to seek out and be receptive to sexual stimuli women then feel sexual arousal, in addition to sexual desire. The cycle results in an enhanced feeling of intimacy. Basson emphasizes the idea that a lack of spontaneous desire should not be taken as an indication of female sexual dysfunction many women experience sexual arousal and responsive desire simultaneously when they are engaged in sexual activity. [30]

Toates's incentive-motivation model Edit

Frederick Toates presented a model of sexual motivation, arousal, and behavior in 2009 that combines the principles of incentive-motivation theory and hierarchical control of behavior. The basic incentive-motivation model of sex suggests that incentive cues in the environment invade the nervous system, which results in sexual motivation. Positive sexual experiences enhance motivation, while negative experiences reduce it. Motivation and behaviour are organized hierarchically each are controlled by a combination direct (external stimuli) and indirect (internal cognitions) factors. Excitation and inhibition of behavior act at various levels of this hierarchical structure. For instance, an external stimulus may directly excite sexual arousal and motivation below a conscious level of awareness, while an internal cognition can elicit the same effects indirectly, through the conscious representation of a sexual image. In the case of inhibition, sexual behavior can be active or conscious (e.g., choosing not to have sex) or it can be passive or unconscious (e.g., being unable to have sex due to fear). Toates emphasizes the importance considering cognitive representations in addition to external stimuli he suggests that mental representations of incentives are interchangeable with excitatory external stimuli for eliciting sexual arousal and motivation. [31]

Bancroft and Janssen's dual control model Edit

This model created by John Bancroft and Erick Janssen, previously at the Kinsey Institute, explores the individual variability of sexual response. They postulate that this variability depends on the interaction between an individual's sexual excitation system (SES) and sexual inhibition system (SIS). Popularized by Emily Nagoski's self-help book Come as You Are, the SES has been described as the sexual response's 'accelerator' and the SIS as the 'brake'. [32] The SIS/SES questionnaire was developed to assess an individual's SIS and SES levels. A factor analysis of the SIS/SES questionnaire, revealed a single excitation factor and two inhibition factors. These inhibition factors were interpreted as SIS1 (inhibition due to the threat of performance failure) and SIS2 (inhibition due to the threat of performance consequences).

The SIS/SES questionnaire was originally developed for men though it has since proven its statistical validity among women. Despite this, the SESII-W (the Sexual Excitation/Sexual Inhibition Inventory for Women) was created by Graham and associates. [33] Female focus groups found that the context of the emotional relationship between sexual partners was not fully represented in the original SIS/SES questionnaire. A factor analysis of this questionnaire revealed only two factors: sexual excitation (SE) and sexual inhibition (SI). This may point to internal inconsistencies in the SIS/SES questionnaire regarding gender. One lower order factor in the SESII-W labeled Arousal Contingency was particularly relevant this factor explains the easy disruption of sexual arousal.

Regardless of the difference in these two questionnaires, both surveys' scores show normal distribution verifying the hypothesis that there is a normal individual variation in sexual arousal and inhibition. In the original SIS/SES questionnaire, statistically significant gender differences are seen despite considerable overlap in scores between men and women. On average, males score higher on sexual excitation and lower than females on both facets of sexual inhibition. As yet, the differences in scores between genders have not been explained beyond the theoretical level.

The source of individual variability on the sexual excitation and inhibition systems is not known definitively. Even less is known about how these systems develop in individuals. Age of first masturbation has been used as a measure to assess sexual development. Age of masturbatory onset is much more variable in girls than boys, whose tend to be close to puberty. [34] Researchers have not determined whether this gender difference is biological in nature or influenced by sociocultural values. One twin-study has found evidence for the heritability of both factors of SIS, but research suggests that SES variability is down to environmental factors. [35]

The majority of studies investigating sexual functioning use heterosexual participants exclusively, unfortunately limiting the generalizability of the dual control model. To date, one study comparing heterosexual and homosexual males found that homosexual men had similar scores for SIS2, but scored significantly higher for SIS1 and SES. [36] Straight, lesbian, and bisexual women's scores on the SESII-W found that bisexual women scored higher on SES than the other groups and straight women scored higher on the sexual inhibition factor than both the lesbian and bisexual women. [37] More studies need to be done using the dual control model to gain a more broad view of sexual orientation and sexual arousability.

One way to study sexual arousal in women and men is to conduct sexual psychophysiological research in a laboratory setting. This field of research looks at physical sexual responses in addition to mental and emotional experiences of sexual arousal. [38]

Experimental studies Edit

Various hypotheses and theories have been propounded in order to establish the biological bases for sexual arousal in humans. Ivan Tarkhanov showed, in experiments on cutting and artificial emptying of the seminal vesicles, that the latter played the crucial role in the generation of sexual excitement in frogs. Proceeding from these experimental results, Tarkhanov put forward a hypothesis that filling and evacuation of the seminal vesicles were the main biological cause which led to sexual arousal and its disappearance in mammals and humans. [39] Ever since Tarkhanov's findings demonstrated sexual arousal in frogs to result from the state of seminal vesicles, the attempted elucidation of their role in other animals' sexual behaviour has been the object of experimental effort. No generalisation has yet appeared, however. The study performed by Beach & Wilson (University of California, Berkeley) in 1964 discovered that these glands do not participate in the regulation of sexual arousal of male rats in the similar manner. [40] Whether the regularity observed in frogs is applicable to humans remains unknown. Unambiguous experimental evidence for the existence of the Tarkhanov regularity in human sexual behaviour has never been obtained. [41] [42]

Another explanation of sexual arousal is offered by the approach which Kazimierz Imieliński calls the "psychohydraulic model of sexuality." This point of view likens human sexuality to a steam boiler, with biological processes or internal irritants creating sexual tension. If the level of this tension reaches threshold, sexual arousal occurs as the expression of necessity to let off steam. Gary F. Kelly (Clarkson University) describes this model as follows:

For centuries, the assumption was made that the longing for sexual interaction was innate, and an inner drive model was used to explain it. It has been suggested that this model was much like a metaphor for a steam boiler. Internal sexual “steam” would build up until the pressure became so great that the drive to release it was very strong. This view also assumed that there was some adverse physical consequence of not releasing the pressure. [43] : 95

The "psychohydraulic model of sexuality" has been formulated most definitely in psychoanalysis:

The instinct causes tensions within the central nervous system which spread out over the whole being it is urgent and irresistible in nature and constantly repeats itself. . An erection, for example, is pleasurable and painful at the same time. With an increase of sexual excitation, the tension increases and becomes wholly unpleasurable. This condition becomes so unbearable that the individual is forced to seek release from these tensions and liberation from the painful feelings. . The pain of tension which accompanies the increase in the intensity of the instinctual drives changes, with the discharge, into the pleasure of relaxation. [44] : 55, 56

After a certain time, the same process begins anew. Such an approach assumes sexual arousal to be a spontaneous desire that appears periodically like sensations of hunger and thirst. Drawing a parallel between these sensations and sexual excitation is widely accepted now: "Everyone must experience sexuality in some way to survive. . In this sense sex is a necessity of life, just as air, food, and warmth." [45] : 190 And yet there is no empirical evidence in support of such a parallel, Imieliński says. Sensations of hunger and thirst occur due to certain states of physiological insufficiency. The feeling of hunger results from the lack of glucose, fats and amino acids in blood. The feeling of thirst occurs in response to reduction of the water content of tissues. None of similar states of physiological deficiency responsible for the periodical appearance of sexual arousal has been revealed in human sexuality. [46]

Females Edit

Sexual arousal in women is characterized by vasocongestion of the genital tissues, including internal and external areas (e.g., vaginal walls, clitoris, and labia). There are a variety of methods used to assess genital sexual arousal in women. Vaginal photoplethysmography (VPG) can measure changes in vaginal blood volume or phasic changes in vasocongestion associated with each heartbeat. Clitoral photoplethysmography functions in a similar way to VPG, but measures changes in clitoral blood volume, rather than vaginal vasocongestion. Thermography provides a direct measure of genital sexual arousal by measuring changes in temperature associated with increased blood flow to the external genital tissues. Similarly, labial thermistor clips measure changes in temperature associated with genital engorgement this method directly measures changes in temperature of the labia. More recently, laser doppler imaging (LDI) has been used as a direct measure of genital sexual arousal in women. LDI functions by measuring superficial changes in blood flow in the vulvar tissues.

Males Edit

The most obvious response involved with sexual behaviour in males is penile erection. The use of the volume (or circumference) change during penile erection as a convenient measure of sexual arousal was first developed by Kurt Freund. [47] This measurement of blood flow to the male genitals is known as penile plethysmography. This is commonly measured using a strain gauge, a simple mercury strain gauge encompassed in a ring of rubber. The ring surrounds the penis, but does not constrict or cause discomfort. [48] The measure has been found by some to be a reliable and valid measurement of male arousal. [49] More recently, thermography has been developed to measure the physiological measurements of sexual arousal. Studies have found temperature change specific to the genitals during sexual arousal, which supports the validity of this measure. [50]

Category-specificity refers to a person showing sexual arousal to the categories of people they prefer to have sex with. Sexual arousal studies involving category-specificity look at genital responses (physiological changes), as well as subjective responses (what people report their arousal levels to be). Category-specific sexual arousal is more commonly found amongst men than women. [51] [52] Heterosexual men experience much higher genital and subjective arousal to women than to men. This pattern is reversed for homosexual men. [53]

Studies have found that women have a non-category-specific genital response pattern of sexual arousal, meaning their genital responses are only modestly related to their preferred category. [54] On the other hand, female subjective responses are category-specific, because they typically report their highest level of arousal to their preferred stimulus, although the reported difference in levels of arousal is typically much smaller than those in men. [55] A possible explanation for the non-category specific genital arousal in women, which also accounts for their high individual variation, is the "preparation hypothesis". This hypothesis suggests that, provided there is enough of an increase in vaginal blood flow for vaginal lubrication to occur in a sexual context, the magnitude of arousal need not be consistent. That is, the hypothesis is that vaginal lubrication can take place as a protective mechanism even in a non-preferred sexual situation, such as when sexual activity is non-consensual. [55]

Other researchers argue that since the research is done on people who volunteer to be studied, the observed levels of category specificity may not represent the population, that there may be different cultural expectations of sexual interests being linked to genital arousal that make men with non-category specific genital arousal less likely to appear as test subjects. There researchers also argue that the assumption that men are always sexually interested in what causes genital arousal removes its own falsifiability by explaining all contradictory data away as "denial", making the theory untestable. [56] [57]

Overlapping brain variables and sexual arousal Edit

While there is disagreement among neurologists on whether or not it is possible to categorically distinguish male brains and female brains by measuring many variables in the brain, neurologists agree that all single variables in the brain display more individual variation and overlap between the sexes than differences between the sexes. For instance, men and women alike are capable of classifying sex acts as sexual no matter if they find them appealing or not, making a genital response to unappealing erotic stimuli a single mechanism step. It is therefore argued by neurologists that category specificity of genital response to erotical imagery, being determined by one or a small number of closely linked brain mechanisms and therefore not subject to significant multivariate effects, cannot be subject to such a large sex difference as that apparent in pletysmographic studies. These neurologists cite the existence of significant volunteering bias among men but not women in erotica research, in particular that the overrepresentation of erectile dysfunction yet underrepresentation of sexuality-related shame in volunteers is consistent with the hypothesis that genital response to both sexual relevance and appeal allows for a stronger erectile function than response only to appeal and that a majority of the male population are ashamed of their responses to unappealing stimuli, accounting for the discrepancy between the report from most heterosexual couples that male erection is faster than female lubrication and the appearance on pletysmography volunteers that female lubrication is at least as fast as male erection. They also argue that the appearance of a greater individual variability in female genital response than in male genital response is consistent with a representative female sample and a male sample subject to bias that leaves much of the individual variability unstudied, with a reference to the neurological observation that all brain structures display significant individual variability in both sexes and that no brain structure is variable only in females and not in males. [58] [59]

Sexual arousal results in a combination of physiological and psychological factors, like genital sexual response and subjective experience of sexual arousal. The degree to which genital and subjective sexual response correspond is termed concordance. Research has shown a reliable gender difference in concordance of sexual arousal, such that men have a higher level of concordance between genital and subjective sexual responding than women do. [60] Some researchers argue that this gender difference can be attributed to the type of method used to assess genital responding in women. There may be a difference in women's ability to perceive internal versus external genital engorgement subjectively, as measured by vaginal photoplethysmography (VPG) and thermography respectively. Chivers and colleagues [61] found that men's and women's concordance was more similar when thermography was used as a measure of genital sexual arousal than when VPG was used. However, few studies using thermography have been conducted and further research is required to determine whether the gender difference in concordance is a measurement artifact or a true phenomenon.

Several hormones affect sexual arousal, including testosterone, cortisol, and estradiol. However, the specific roles of these hormones are not clear. [62] Testosterone is the most commonly studied hormone involved with sexuality. It plays a key role in sexual arousal in males, with strong effects on central arousal mechanisms. [62] The connection between testosterone and sexual arousal is more complex in females. Research has found testosterone levels increase as a result of sexual cognitions in females that do not use hormonal contraception. [63] Also, women who participate in polyandrous relationships have higher levels of testosterone. However, it is unclear whether higher levels of testosterone cause increased arousal and in turn multiple partners or whether sexual activity with multiple partners cause the increase in testosterone. [64] Inconsistent study results point to the idea that while testosterone may play a role in the sexuality of some women, its effects can be obscured by the co-existence of psychological or affective factors in others. [62]

While human sexuality is well understood, scientists do not completely grasp how other animals relate sexually. However, current research studies suggest that many animals, like humans, enjoy sexual relations that are not limited to reproduction. Dolphins and bonobos, for example, are both well known to use sex as a "social tool to strengthen and maintain bonds." [65] Ethologists have long documented the exchanges of sex to promote group cohesion in social animals. Cementing social bondage is one of the most prominent theorized selective advantages of group selection theory. Experts in the evolution of sex such as John Maynard Smith advocate for the idea that the exchange of sexual favors helps congeal and localize the assortment of alleles in isolated population and therefore is potentially a very strong force in evolution. Maynard Smith has also written extensively on the "seminal fluid swapping theory" logistic application of the assortment of alleles as a more accurate synthetic depiction of the Hardy–Weinberg principle in cases of severely interbreeding populations.

The effect of sexual response is thought to be a plastic positive reinforcement behavior modifier associated with the Baldwin effect. The display of secondary sex characteristics in humans such as a penis-like enlarged clitoris in females during arousal and gynecomastia in males are thought to have once been objects of mate selection in human evolution because of the persistence of the phenomenon of these features invoking sexual arousal for potential mates in cross-cultural studies. [66] A dramatic example of this is the high rates of secondary sex characteristic dimorphism in some Southeast Asia human populations. [67] Similar evolutionary stimuli may also have resulted in novel structures such as the pseudo-penis of the female spotted hyena. [68]

Psychological aspects

Physiology sets only very broad limits on human sexuality most of the enormous variation found among humans must be attributed to the psychological factors of learning and conditioning.

The human infant is born simply with the ability to respond sexually to tactile stimulation. It is only later and gradually that the individual learns or is conditioned to respond to other stimuli, to develop a sexual attraction to males or females or both, to interpret some stimuli as sexual and others as nonsexual, and to control in some measure his or her sexual response. In other words, the general and diffuse sexuality of the infant becomes increasingly elaborated, differentiated, and specific.

The early years of life are, therefore, of paramount importance in the development of what ultimately becomes adult sexual orientation. There appears to be a reasonably fixed sequence of development. Before age five, children develop a sense of gender identity, think of themselves as boys or girls, and begin to relate to others differently according to their gender. Through experience children learn what behaviour is rewarded and what is punished and what sorts of behaviour are expected of them. Parents, peers, and society in general teach and condition children about sex not so much by direct informational statements and admonitions as by indirect and often unconscious communication. Children soon learn, for example, that they can touch any part of their body or someone else’s body except the anal–genital region. Children rubbing their genitals find that this quickly attracts adult attention and admonishment or that adults will divert them from this activity. It becomes clear that there is something peculiar and taboo about this area of the body. This “genital taboo” is reinforced by the great concern over children’s excretory behaviour: bladder and bowel control is praised loss of control is met by disappointment, chiding, and expressions of disgust. Obviously, the anal–genital area is not only a taboo area but a very important one as well. It is almost inevitable that the genitalia become associated with anxiety and shame. It is noteworthy that this attitude finds expression in the language of Western civilizations, as in “privates” (something to be kept hidden) and the German word for the genitals, Scham (“shame”).

While all children in Western civilizations experience this antisexual teaching and conditioning, a few have, in addition, atypical sexual experiences, such as witnessing or hearing sexual intercourse or having sexual contact with an older person. The effects of such atypical experiences depend upon how children interpret them and upon the reaction of adults if the experience comes to their attention. Seeing parental coitus is harmless if children interpret it as playful wrestling but harmful if they consider it as hostile, assaultive behaviour. Similarly, an experience with an adult may seem merely a curious and pointless game, or it may be a hideous trauma leaving lifelong psychic scars. In many cases the reaction of parents and society determines the child’s interpretation of the event. What would have been a trivial and soon-forgotten act becomes traumatic if the mother cries, the father rages, and the police interrogate the child.

Some atypical developments occur through association during the formative years. A child may associate clothing, especially underclothing, stockings, and shoes with gender and sex and thereby establish the basis for later fetishism or transvestism. Others, having been spanked or otherwise punished for self-masturbation or childhood sex play, form an association between punishment, pain, and sex that could escalate later into sadism or masochism. It is not known why some children form such associations whereas others with apparently similar experience do not.

About the age that children enter puberty, parents and society, who more often than not refuse to recognize that children have sexual responses and capabilities, finally face the inescapable reality and consequently begin inculcating children with their attitudes and standards regarding sex. This campaign by adults is almost wholly negative: the child is told what not to do. While dating may be encouraged, no form of sexual activity is advocated or held up as model behaviour. The message usually is: “Be popular [i.e., sexually attractive] but abstain from sexual activity.” This antisexualism is particularly intense regarding young females and is reinforced by reference to pregnancy, sexually transmitted diseases, and, most importantly, social disgrace. To this list religious families add the concept of the sinfulness of premarital sexual expression. With young males the double standard of morality still prevails. The youth receives a double message: “Don’t do it, but we expect that you will.” No such loophole in the prohibitions is offered young girls. Meanwhile, the young male’s peer group is exerting a prosexual influence, and his social status is enhanced by his sexual exploits or by exaggerated reports thereof.

As a result of this double standard of sexual morality, the relationship between young males and females often becomes a ritualized contest, the male attempting to escalate the sexual activity and the female resisting his efforts. Instead of mutuality and respect, one often has a struggle in which the female is viewed as a reluctant sexual object to be exploited, and the male is viewed as a seducer and aggressor who must succeed in order to maintain his self-image and his status with his peers. This sort of pathological relationship causes a lasting attitude on the part of females: men are not to be trusted they are interested only in sex a girl dare not smile or be friendly lest males interpret it as a sign of sexual availability, and so forth. Such an aura of suspicion, hostility, and anxiety is scarcely conducive to the development of warm, trusting relationships between males and females. Fortunately, love or infatuation usually overcomes this negativism with regard to particular males, but the average female still maintains a defensive and skeptical attitude toward men.

Western society is replete with attitudes that impede the development of a healthy attitude toward sex. The free abandon so necessary to a full sexual relationship is, in the eyes of many, an unseemly loss of self-control, and self-control is something one is urged to maintain from infancy onward. Panting, sweating, and involuntary vocalization are incompatible with the image of dignity. Worse yet is any substance once it has left the body: it immediately becomes unclean. The male and female genital fluids are generally regarded with disgust—they are not only excretions but sexual excretions. Here again, societal concern over excretion is involved, for sexual organs are also urinary passages and are in close proximity to the “dirtiest” of all places—the anus. Lastly, many individuals in society regard menstrual fluid with disgust and abstain from sexual intercourse during the four to six days of flow. This attitude is formalized in Judaism, in which menstruating females are specifically labelled as ritually unclean.

In view of all these factors working against a healthy, rational attitude toward sex and in view of the inevitable disappointments, exploitations, and rejections that are involved in human relationships, one might wonder how anyone could reach adulthood without being seriously maladjusted. The sexual impulse, however, is sufficiently strong and persistent and repeated sexual activity gradually erodes the inhibitions and any sense of guilt or shame. Further, all humans have a deep need to be esteemed, wanted, and loved. Sexual activity with another is seen as proof that one is attractive, desired, valued, and possibly loved—a proof very necessary to self-esteem and happiness. Hence, even among the very inhibited or those with weak sex drive, there is this powerful motivation to engage in sociosexual activity.

Most persons ultimately achieve at least a tolerable sexual adjustment. Some unfortunates, nevertheless, remain permanently handicapped, and very few completely escape the effects of society’s antisexual conditioning. While certain inhibitions and restraints are socially and psychologically useful—such as deferring gratification until circumstances are appropriate and modifying activity out of regard for the feelings of others—most people labour under an additional burden of useless and deleterious attitudes and restrictions.

The term bisexual describes the disposition to be attracted to both sexes. The presence of bisexuality is higher among females. (LeVay, Simon and Janice Baldwin. Human Sexuality. p 166-180. MA: Sinauer Associates, Inc., Third Edition, 2009.)

A bisexual individual has the potential to be sexually/romantically attracted to more than one sex, but not necessarily at the same time or to the same degree. (Baumgardner, Jennifer. Look Both Ways—Bisexual Politics. p 41-60. NY: Farrar, Straus and Giroux. 2008.)

Bisexual men are often married and engage in casual sex with other males for variety. Bisexual women seek long-term relationships with members of either gender and are more likely to alternate partners. (Wilson, Glenn. The Great Sex Divide. p 86-87. England: Peter Owen Publishers, 1989.)


The most commonly asked question about pedophilia is how frequently it occurs. Obtaining reliable incidence numbers of pedophilia as a preference disorder is difficult as individuals are typically unwilling to admit pedophilic preferences, particularly when offenses have been committed. The prevalence of pedophilia in the general population is not known. The prevalence of a true pedophilic sexual preference is approximately 1%, but when general fantasies are investigated, that prevalence can reach up to 5% among men in the general population.

Some studies suggest that the prevalence of pedophilia may be between 3%-5% in the general population (as reviewed by Seto, 2009). In penile plethysmography, studies of men with sexual offense histories against children, these prevalences can jump from 30% for men with one offense to 61% for men with three or more sexual offenses against children (Blanchard, 2010 Seto, 2009). The most well-known objective method of measuring pedophilic interest is penile plethysmography (PPG) or phallometry. This method measures genital sexual arousal through sexual stimuli and is based on the relative change in penile response. Sexual preference can be determined as the relative change in penile response to various classes of sexual stimuli (according to Tanner scales), such as prepubescent, pubescent, or adult female or male targets. [6]

Less is known about the prevalence of pedophilia in women, but there are case reports of women with strong sexual fantasies and urges towards children. Frequently, the abuse against a child is carried out in collaboration with a male partner or victims are seen as surrogates to replace less than desirable relationships. The 2009 Plymouth child abuse case was a child abuse and pedophile ring involving at least five adults from different parts of England who all met on Facebook. The case centered on photographs taken of up to 64 children aged two to five years old by Vanessa George, a nursery (pre-school) worker in Plymouth. It highlighted the issue of child molestation by women, as all but one of the members of the ring were female. The case prompted an increased recognition of the problem of female pedophiles, sex offenders, and the scale of their offending, with one estimate suggesting that at least 10% of sex offenders are female.

Currently, there is no reliable estimate of pedophilia in women and the question remains whether pedophilia, as currently defined, even exists in women [7] .The true number of female child molesters may be underrepresented by available estimates, for reasons including a “societal tendency to dismiss the negative impact of sexual relationships between young boys and adult women, as well as women’s greater access to very young children who cannot report their abuse,” among other explanations (e.g., Vanessa George who worked with children under the age of 5).

T he reason that there is very little known about the prevalence of pedophilia at this time may be because of the severely negative stigma associated with having p edophilia , and therefore , many people with pedophilia only rarely seek help from a mental health professional. Also, abnormal psychology has studied egosyntonic and egodystonic concepts in some detail. Egosyntonic refers to the behaviors, values, and feelings that are in harmony with or acceptable to the needs and goals of the ego, or consistent with one’s ideal self-image. Egodystonic (or ego alien ) is the opposite, referring to thoughts and behaviors (dreams, compulsions, desires, etc.) that are in conflict, or dissonant, with the needs and goals of the ego, or, further, in conflict with a person’s ideal self-image. Many mental disorders, including pedophilic disorder, are egosyntonic, which makes their treatment difficult as the patients may not perceive anything wrong and view their perceptions and behavior as reasonable and appropriate. This corresponds to the general concept in psychiatry of poor insight.

Ego-dystonic sexual orientation includes people who acknowledge that they have a sexual preference for prepubertal children, but wish to change it due to the associated psychological or behavioral problems (or both).


Let us return to our initial questions: Are the results of functional neuroimaging experiments consistent with the Freudian model of sexual drives? Can modern studies help psychoanalysis to reformulate certain aspects of this model? In spite of the above-mentioned limitations, functional neuroimaging studies of SA have thrown a new light on the four fundamental characteristics of sexual drives by identifying their potential neural correlates. The neurophenomenological model based on these studies includes: (i) brain areas involved in assessing visual targets as congruent, or not, with the objects of sexual drives (ii) brain areas related to the motor factor of drives and to their aims, the aims being understood here as specific action patterns (iii) neural structures that may contribute to the source of sexual drives and (iv) neural correlates of emotions involved in SA, in particular pleasure and tension. In addition, functional neuroimaging sudies demonstrate the neural correlates of the autonomic and neuroendocrine aspects of SA. Finally, neuroimaging studies have begun to identify the neural correlates of three barriers to the inappropriate expression of drives: moral feelings, temporary or enduring devaluation of sexual targets and refraining from sexual acts once SA has occurred.

The main difference emerging between the functional neuroimaging perspective and the Freudian theory relates to the source of drives. At least in adult subjects, the process of excitation occurring in a peripheral organ does not seem to be an indispensable part of the determinants of SA. It is rather the central processing of sensory stimuli that gives them their sexually arousing and sexually pleasurable character. Thus, as predicted by Freud, biology, here represented by functional neuroimaging studies, may have thrown some light on “the most obscure part of the psychoanalytic theory of drives” and begun to return some answers to the questions psychoanalysis has put to it (Freud, 1920).


Simulator Sickness

Table 1 shows the means and SDs for the SSQ Total score as a function of Group, Condition, and Time point. In order to explore if the experimental conditions enhanced simulator sickness symptoms, the SSQ was applied before and after each experimental condition. The linear mixed model for the Total score of the SSQ revealed neither a significant main effect nor a significant interaction (see Table 2). Thus, wearing a HMD did not resulted in enhanced simulator sickness symptoms.

Sense of presence

Table 3 shows means and SDs of the IPQ sub-scales as a function of subject Group and Condition. Table 4 shows the results of the linear mixed models. The linear mixed model for the General item (“sense of being there”) only revealed a significant main effect for Condition, F(2,84) = 40.12, p <.001. Post-hoc pairwise comparisons showed in line with hypothesis 1, that the conventional condition resulted in a significantly lower feeling of being there than the immersive condition, t(92.19) = -8.48, p <.001, d = 1.74, or the immersive+ condition, t(92.19) = -10.49, d = 2.19, p <.001. Against hypothesis 1, the immersive+ and the immersive condition did not differ significantly, t(92.19) = -2.01, p = .12, d = .42.

The linear mixed model for the sub-scale Spatial presence, too, only revealed a significant main effect for condition, F(2,86) = 3.63, p = .03. Post-hoc pairwise comparisons showed that the conventional condition resulted in a significantly lower spatial presence than the immersive condition, t(86) = -3.59, p = .002, d = .77, or the immersive+ condition, t(86) = -3.73, p = .001, d = .80. There was no significant difference between the immersive+ and the immersive condition, t(86) = -.14, p = .989, d = .03.

The linear mixed model for the sub-scale Involvement revealed a significant main effect for condition, F(2,86) = 65.17, p <.001, and a significant main effect for Subject group, F(1,81.37) = 5.52, p = .020. Gynephilic subjects experienced higher involvement than androphilic subjects. Post-hoc pairwise comparisons showed that the conventional condition resulted in a significantly lower involvement than the immersive condition, t(86) = -9.85, p <.001, d = 2.12, or the immersive+ condition, t(86) = -12.51, p <.001, d = 2.70. In line with hypothesis 1, the immersive+ results in a significant higher involvement than the immersive condition, t(86) = -2.66, p = .025, d = .57.

The linear mixed model for the sub-scale Experienced Realism revealed only a significant main effect for condition, F(2,86) = 43.64, p <.001. Post-hoc pairwise comparisons showed that the conventional condition resulted in a significantly lower involvement than the immersive condition, t(94.19) = -9.02, p <.001, d = 1.86, or the immersive+ condition, t(94.19) = -10.91, p <.001, d = 2.25. But there was no significant difference between the immersive+ and the immersive condition, t(94.19) = -1.89, p = .148, d = .39.

Realism of virtual characters

Means and SDs for the subjective ratings of the realism of the virtual characters are provided in Table 5. The linear mixed model revealed a significant main effect for Subject group, F(1,43) = 6.10, p = .020, and a significant main effect for Condition, F(2,41.90) = 20.89, p <.001. All other main effects or interactions were not significant (see Table 6). Androphilic subjects rated virtual characters altogether as significantly more realistic than gynephilic subjects. Post-hoc pairwise comparisons further showed, that virtual characters were perceived as significantly more realistic in the immersive+ condition than in the conventional, t(47.10) = -7.19, p <.001, d = 2.10, or in the immersive condition, t(47.05) = -4.08, p <.001, d = 1.19. Also, virtual characters were rated as significantly more realistic in the immersive condition than in the conventional condition, t(47.13) = -4.82, p <.001, d = 1.14.

Sexual Attractiveness of virtual characters

Means and SDs for the subjective ratings of the realism of the virtual characters are provided in Table 5, the results of the linear mixed model in Table 6. The linear mixed model revealed a significant three-factorial Group × Gender of virtual character × Condition interaction, F(2,42.07) = 18.94, p <.001. Fig 3 shows the significant three-factorial Group × Gender × Condition interaction and the results of the post-hoc pairwise comparisons. Post-hoc pairwise comparisons showed for each experimental condition that gynephilic subjects rated female characters as significantly more sexually attractive than male characters, conventional: t(63.94) = -5.89, p <.001, d = 1.47, immersive: t(63.13) = -7.70, p <.001, d = 1.94, immersive+: t(62.78) = -7.70, p <.001, d = 1.94. Androphilic subjects rated male characters as significantly more sexually attractive than female characters in each condition, conventional: t(62.49) = 5.50, p <.001, d = 1.39, immersive: t(61.33) = 5.75, p <.001, d = 1.47, immersive+: t(61.12) = 7.45, p <.001, d = 1.91.

Sexual attractiveness rating comprised a 6-point Likert scale ranging from 0 (not sexually attractive) to 5 (very sexually attractive). Blue lines represent mean sexual attractiveness ratings for female virtual characters, black lines mean sexual attractiveness ratings for male virtual characters. * p <.05, ** p <.01, *** p <.001.

Gynephilic subjects differed in their sexual attractiveness ratings between the experimental conditions only regarding female characters, androphilic subjects ratings differed only regarding male characters. Gynephilic subjects rated female characters in the immersive+ condition, t(45.62) = -7.30, p <.001, d = 2.16, as well as in the immersive condition as more sexually attractive than in the conventional condition, t(46.24) = -5.41, p <.001, d = 1.59. However, there was no significant difference between the immersive+ and the immersive condition, t(50.39) = -2.47, p = .158, d = .70. Androphilic subjects rated male characters in the immersive+ condition, t(44.90) = -5.99, p <.001, d = 1.80, as well as in the immersive condition as more sexually attractive than in the conventional condition, t(43.05) = -3.62, p = .008, d = 1.10. Nevertheless, there was only a borderline significant trend between the immersive+ and the immersive condition, t(43.80) = -2.83, p = .072, d = .86.

Viewing Time

Means and SDs for the viewing time are provided in Table 5, all results of the linear mixed model in Table 6. The linear mixed model revealed a significant three-factorial Group × Gender of virtual character × Condition interaction, F(2,42.03) = 11.16, p <.001. Fig 4 shows the significant three-factorial Group × Gender × Condition interaction and the results of the post-hoc pairwise comparisons. Post-hoc pairwise comparisons showed in line with hypothesis 3, that gynephilic participants looked significantly longer at female than at male characters. This holds true for all three experiments, conventional: t(48.52) = -3.91, p = .002, d = 1.12, immersive: t(50.04) = -4.11, p <.001, d = 1.16, immersive+: t(47.79) = -4.95, p <.001, d = 1.43. Androphilic subjects looked significantly longer at male characters than at female characters in all three experimental conditions, conventional: t(48.74) = 3.94, p = .001, d = 1.13, immersive: t(49.97) = 4.40, p <.001, d = 1.24, immersive+: t(47.83) = 3.40, p = .002, d = .98.

Blue lines represent mean viewing times for female virtual characters, black lines mean viewing times for male virtual characters. * p <.05, ** p <.01, *** p <.001.

For gynephilic subjects post-hoc pairwise comparisons showed, regarding the viewing time for male characters, a significant difference only between the conventional condition and the immersive+ condition, t(46.79) = -3.89, p = .004. Viewing times for female characters differed significantly between the conventional and the immersive+ condition, t(46.71) = -8.59, p <.001, d = 2.51, as well as between the immersive and the immersive+ condition, t(46.82) = -7.91, p <.001, d = 2.31. There was no significant difference between the immersive and the conventional condition, t(45.87) = -.93, p = .936, d = .27. Androphilic subjects showed no significant differences in their viewing times for female characters between the three experimental conditions. However, they looked longer at male characters in the immersive+ condition than in the conventional condition, t(46.93) = -6.52, p <.001, d = 1.90, or in the immersive condition, t(47.07) = -4.30, p = .001, d = 1.25. There was no significant difference between the immersive and the conventional condition, t(46.80) = -.86, p = .948, d = .25.

Turn arounds in the immersive+ condition

In order to analyze to what extend subjects turned around the virtual characters in the immersive+ condition, the sum of degrees subjects turned around each character was analyzed. The linear mixed model revealed a significant Group × Gender interaction, F(1,43.08) = 38.62, p <.001. Post-hoc pairwise comparisons showed that gynephilic subjects turned significantly more often around female characters (M = 344.24, SD = 291.29) than around male characters (M = 141.74, SD = 163.86), t(63.82) = -7.10, p <.001, d = 1.78. Androphilic subjects turned significantly more degrees around male (M = 294.05, SD = 183.64) than female characters (M = 143.22, SD = 144.91), t(62.22) = -6.01, p <.001, d = 1.52.

Sexual orientation index (SOI) and discriminant validity

The Sexual Orientation Index (SOI) was defined as the difference between the viewing time for female characters and the viewing time for male characters. Table 7 shows means and SDs of the sexual orientation index as a function of subject Group and Condition. The linear mixed model revealed a significant Group × Condition interaction, F(2,86) = 17.83, p <.001. Post-hoc pairwise comparisons revealed that the SOI was, in all three experimental conditions, significantly higher in the gynephilic group than in the androphilic group (conventional: t(109.02) = 3.17, p = .002, d = 2.16 immersive: t(109.02) = 3.67, p <.001, d = 1.63 immersive+: t(109.02) = 9.14, p <.001), d = 1.78. Furthermore, the SOI was, in the gynephilic group, higher in the immersive+ condition than in the conventional condition, t(94.19) = 4.26, p <.001, d = .88, or in the immersive condition, t(94.19) = 4.01, p <.001, d = .83. There was no significant difference between the conventional and the immersive condition, t(94.19) = .24, p = .969, d = .05. Androphilic subjects showed a significantly lower SOI in the immersive+ condition than in the conventional condition, t(94.19) = 3.42, p = .003, d = .70, or in the immersive condition, t(94.19) = 3.03, p = .009, d = .62. There was again no difference between the conventional and the immersive condition, t(94.19) = .39, p = .920, d = .08.

In order to test how well the three experiments can distinguish regarding the sexual orientation of the subjects, ROC analyses were performed based on the SOI. ROC analysis revealed an AUC of.952 (95%-CI:.893—1.00) for the conventional condition. Using a cut-off criterion of -100.65 ms, the conventional condition differed between gynephilic and androphilic subjects with a sensitivity of 95% and a specificity of 88%. ROC analysis demonstrated an AUC of.944 (95%-CI:.882—1.0) for the immersive condition, resulting in a sensitivity of 90% and a specificity of 88% (by using a cut-off criterion of -34.93 ms). Finally, ROC analysis revealed an AUC of.962 (95%-CI:.909—1.00) for the immersive+ condition. Using a cut-off criterion of -578.11 ms, the immersive+ condition demonstrated a sensitivity of 90% and a specificity of 96%. From a statistical point of view, the discriminant validity of conventional condition did not differ from the discriminant validity of the immersive condition, Z = -0.19, p = .853, or the immersive+ condition, Z = -.273, p = .783. Also, there was no significant difference between the immersive and the immersive+ condition, Z = .425, p = .671.

The Orgasmic Mind: This Is Your Brain On Sex

By Martin Portner
Scientific American

She did not often have such strong emotions. But she suddenly felt powerless against her passion and the desire to throw herself into the arms of the cousin whom she saw at a family funeral.

“It can only be because of that patch,” said Marianne, a participant in a multinational trial of a testosterone patch designed to treat hypoactive sexual desire disorder, in which a woman is devoid of libido. Testosterone, a hormone ordinarily produced by the ovaries, is linked to female sexual function, and the women in this 2005 study had undergone operations to remove their ovaries.

After 12 weeks of the trial, Marianne had felt her sexual desire return. Touching herself unleashed erotic sensations and vivid sexual fantasies. Eventually she could make love to her husband again and experienced an orgasm for the first time in almost three years.

But that improvement was not because of testosterone, it turned out. Marianne was among the half of the women who had received a placebo patch—with no testosterone in it at all.

Marianne’s experience underlines the complexity of sexual arousal. Far from being a simple issue of hormones, sexual desire and orgasm are subject to various influences on the brain and nervous system, which controls the sex glands and genitals. And many of those influences are environmental.

Recent research, for example, shows that visual stimuli spur sexual stirrings in women, as they do in men. Marianne’s desire may have been invigorated by conversations or thoughts about sex she had as a result of taking part in the trial. Such stimuli may help relieve inhibitions or simply whet a person’s appetite for sex.

Achieving orgasm, brain-imaging studies show, involves more than heightened arousal. It requires a release of inhibitions and control in which the brain’s center of vigilance shuts down in males in females, various areas of the brain involved in controlling thoughts and emotions become silent.

The brain’s pleasure centers tend to light up brightly in the brain scans of both sexes, especially in those of males. The reward system creates an incentive to seek more sexual encounters, with clear benefits for the survival of the species. When the drive for sex dissipates, as it did with Marianne, people can reignite the spark with tactics that target the mind.

Biologists identified sex hormones such as estrogen and testosterone in the 1920s and 1930s, and the first studies of human sexuality appeared in the 1940s. In 1948 biologist Alfred Kinsey of Indiana University introduced his first report on human sexual practices, Sexual Behavior in the Human Male, which was followed, in 1953, by Sexual Behavior in the Human Female.

These highly controversial books opened up a new dialogue about human sexuality. They not only broached topics—such as masturbation, homosexuality and orgasm—that many people considered taboo but also revealed the surprising frequency with which people were coupling and engaging in sexual relations of countless varieties.

Kinsey thus debuted sex as a science, paving the way for others to dig below statistics into the realm of biology. In 1966 gynecologist William Masters and psychologist Virginia Johnson—who originally hailed from Washington University before founding their own research institute in St. Louis—described for the first time the sexual response cycle (how the body responds to sexual stimulation), based on observations of 382 ­women and 312 men undergoing some 10,000 such cycles. The cycle begins with excitation, as blood rushes to the penis in men, and as the clitoris, vulva and vagina enlarge and grow moist in women. Gradually, people reach a plateau, in which they are fully aroused but not yet at orgasm. After reaching orgasm, they enter the resolution phase, in which the tissues return to the preexcitation stage.

In the 1970s psychiatrist Helen Singer Kaplan of the Human Sexuality Program at Weill Medical College of Cornell University added a critical element to this cycle—desire—based on her experience as a sex therapist. In her three-stage model, desire precedes sexual excitation, which is then followed by orgasm. Because desire is mainly psychological, Kaplan emphasized the importance of the mind in the sexual experience and the destructive forces of anxiety, defensiveness and failure of communication.

In the late 1980s gynecologist Rosemary Basson of the University of British Columbia proposed a more circular sexual cycle, which, despite the term, had been described as a largely linear progression in previous work. Basson suggested that desire might both lead to genital stimulation and be invigorated by it. Countering the idea that orgasm is the pinnacle of the experience, she placed it as a mere spot on the circle, asserting that a person could feel sexually satisfied at any of the stages leading up to an orgasm, which thus does not have to be the ultimate goal of sexual activity.

Given the importance of desire in this cycle, researchers have long wanted to identify its key ingredients. Conventional wisdom casts the male triggers in simplistic sensory terms, with tactile and visual stimuli being particularly enticing.

Men are drawn to visual erotica, explaining the lure of magazines such as Playboy. Meanwhile female desire is supposedly fueled by a richer cognitive and emotional texture. “Women experience desire as a result of the context in which they are inserted—whether they feel comfortable with themselves and the partner, feel safe and perceive a true bond with the partner,” opines urologist Jennifer Berman of the Female Sexual Medicine Center at the University of California, Los Angeles.

Yet sexual imagery devoid of emotional connections can arouse women just as it can men, a 2007 study shows. Psychologist Meredith Chivers of the Center for Addiction and Mental Health in Toronto and her colleagues gauged the degree of sexual arousal in about 100 women and men, both homosexual and heterosexual, while they watched erotic film clips. The clips depicted same-sex intercourse, solitary masturbation or nude exercise—performed by men and women—as well as male-female intercourse and mating between bonobos (close ape relatives of the chimpanzee).

The researchers found that although nude exercise genitally aroused all the onlookers the least and intercourse excited them the most, the type of actor was more important for the men than for the women. Heterosexual women’s level of arousal increased along with the intensity of the sexual activity largely irrespective of who or what was engaged in it. In fact, these women were genitally excited by male and female actors equally and also responded physically to bonobo copulation. (Gay women, however, were more particular they did not react sexually to men masturbating or exercising naked.)

The men, by contrast, were physically titillated mainly by their preferred category of sexual partner—that is, females for straight men and males for gay men—and were not excited by bonobo copulation. The results, the researchers say, suggest that women are not only aroused by a variety of types of sexual imagery but are more flexible than men in their sexual interests and preferences.

When it comes to orgasm, simple sensations as well as higher-level mental processes probably also play a role in both sexes. Although Kinsey characterized orgasm in purely physical terms, psychologist Barry R. Komisaruk of Rutgers University has defined the experience as more multifaceted. In their book The Science of Orgasm (Johns Hopkins University Press, 2006), Komisaruk, endocrinologist Carlos Beyer-Flores of the Tlaxcala Laboratory in Mexico and Rutgers sexologist Beverly Whipple describe orgasm as maximal excitation generated by a gradual summing of responses from the body’s sensory receptors, combined with complex cognitive and emotional forces. Similarly, psychologist Kent Berridge of the University of Michigan at Ann Arbor has described sexual pleasure as a kind of “gloss” that the brain’s emotional hub, the limbic system, applies over the primary sensations.

The relative weights of sensory and emotional influences on orgasm may differ between the sexes, perhaps because of its diverging evolutionary origins. Orgasm in men is directly tied to reproduction through ejaculation, whereas female orgasm has a less obvious evolutionary role. Orgasm in a woman might physically aid in the retention of sperm, or it may play a subtler social function, such as facilitating bonding with her mate. If female orgasm evolved primarily for social reasons, it might elicit more complex thoughts and feelings in women than it does in men.

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But does it? Researchers are trying to crack this riddle by probing changes in brain activity during orgasm in both men and women. Neuroscientist Gert Holstege of the University of Gro­ningen in the Netherlands and his colleagues attempted to solve the male side of the equation by asking the female partners of 11 men to stimulate their partner’s penis until he ejaculated while they scanned his brain using positron-emission tomography (PET). During ejaculation, the researchers saw extraordinary activation of the ventral tegmental area (VTA), a major hub of the brain’s reward circuitry the intensity of this response is comparable to that induced by heroin. “Because ejaculation introduces sperm into the female reproductive tract, it would be critical for reproduction of the species to favor ejaculation as a most rewarding behavior,” the researchers wrote in 2003 in The Journal of Neuroscience.

The scientists also saw heightened activity in brain regions involved in memory-related imagery and in vision itself, perhaps because the volunteers used visual imagery to hasten orgasm. The anterior part of the cerebellum also switched into high gear. The cerebellum has long been labeled the coordinator of motor behaviors but has more recently revealed its role in emotional processing. Thus, the cerebellum could be the seat of the emotional components of orgasm in men, perhaps helping to coordinate those emotions with planned behaviors. The amygdala, the brain’s center of vigilance and sometimes fear, showed a decline in activity at ejaculation, a probable sign of decreasing vigilance during sexual performance.

To find out whether orgasm looks similar in the female brain, Holstege’s team asked the male partners of 12 women to stimulate their partner’s clitoris—the site whose excitation most easily leads to orgasm—until she climaxed, again inside a PET scanner. Not surprisingly, the team reported in 2006, clitoral stimulation by itself led to activation in areas of the brain involved in receiving and perceiving sensory signals from that part of the body and in describing a body sensation—for instance, labeling it “sexual.”

But when a woman reached orgasm, something unexpected happened: much of her brain went silent. Some of the most muted neurons sat in the left lateral orbitofrontal cortex, which may govern self-control over basic desires such as sex. Decreased activity there, the researchers suggest, might correspond to a release of tension and inhibition. The scientists also saw a dip in excitation in the dorsomedial prefrontal cortex, which has an apparent role in moral reasoning and social judgment—a change that may be tied to a suspension of judgment and reflection.

Brain activity fell in the amygdala, too, suggesting a depression of vigilance similar to that seen in men, who generally showed far less deactivation in their brain during orgasm than their female counterparts did. “Fear and anxiety need to be avoided at all costs if a woman wishes to have an orgasm we knew that, but now we can see it happening in the depths of the brain,” Holstege says. He went so far as to declare at the 2005 meeting of the European Society for Human Reproduction and Development: “At the moment of orgasm, women do not have any emotional feelings.”

But that lack of emotion may not apply to all orgasms in women. Komisaruk, Whipple and their colleagues studied the patterns of brain activation that occur during orgasm in five women with spinal cord injuries that left them without sensation in their lower extremities. These women were able to achieve a “deep,” or nonclitoral, orgasm through mechanical stimulation (using a laboratory device) of the vagina and cervix. But contrary to Holstege’s results, Komisaruk’s team found that orgasm was accompanied by a general activation of the limbic system, the brain’s seat of emotion.

Among the activated limbic regions were the amygdala and the hypothalamus, which produces oxytocin, the putative love and bonding hormone whose levels jump fourfold at orgasm. The researchers also found heightened activity in the nucleus accumbens, a critical part of the brain’s reward circuitry that may mediate orgasmic pleasure in women. In addition, they saw unusual activity in the anterior cingulate cortex and the insula, two brain areas that Rutgers anthropologist Helen Fisher has found come to life during the later stages of love relationships. Such activity may connect a female’s sexual pleasure with the emotional bond she feels with her partner.

Disentangling the connections between orgasm, reproduction and love may someday yield better medications and psychotherapies for sexual problems. As Marianne’s case illustrates, the answer is usually not as simple as a hormone boost. Instead her improvement was probably the result of the activation or inactivation of relevant parts of her brain by social triggers she encountered while participating in an experiment whose purpose centered on female sexual arousal. Indeed, many sex therapies revolve around opening the mind to new ways of thinking about sex or about your sexual partner.

Companies are also working on medications that act on the nervous system to stimulate desire. One such experimental compound is a peptide called bremelanotide, which is under development by Palatin Technologies in Cranbury, N.J. It blocks certain receptors in the brain that are involved in regulating basic drives such as eating and sex. In human studies bremelanotide has prompted spontaneous erections in men and boosted sexual arousal and desire in women, but the U.S. Food and Drug Administration has held up its progress out of concern over side effects such as rising blood pressure.

Continued scientific dissection of the experience of orgasm may lead to new pharmaceutical and psychological avenues for enhancing the experience. Yet overanalyzing this moment of intense pleasure might also put a damper on the fun. That is what the science tells us anyway.