The changes in brain activity that accompany orgasm are similar in many respects to those observed during other forms of highly rewarding or pleasurable activity, including the consumption of recreational drugs. Many different parts of the brain are activated during orgasm, among them the nucleus accumbens and the anterior cingulate. As we shall see later, these two brain regions play prominent roles in mediating the experience of pleasure. We know that these areas of the brain are more active during orgasm because doughty volunteers have been willing and able to push back the frontiers of knowledge by masturbating to orgasm inside a functional magnetic resonance imaging (fMRI) machine.3
Orgasm is accompanied by involuntary muscle contractions in the perineum and rectum. Needless to say, scientists have measured these as well. In one study, researchers at the University of Groningen in the Netherlands persuaded twenty-three healthy women to have a measuring instrument inserted into their rectum to record these muscle contractions. The women were then monitored while having real orgasms, produced by clitoral stimulation, and also when faking orgasms. The data revealed that when a woman has a genuine orgasm – as opposed to a fake one – her rectum palpitates at a frequency of between 8 and 13 hertz (cycles per second). Fluctuating rectal pressure in the frequency band 8–13 hertz was an accurate indicator of genuine clitoral orgasm. Faking an orgasm, or masturbating to just short of orgasm, did not generate this signature response.4
Orgasm also triggers the release of the hormone oxytocin, a substance which is perhaps better known for stimulating the flow of milk from the breasts. Oxytocin contributes to the formation of the pair-bond between sexual partners. Some of the clearest evidence for this comes from research on voles. In monogamous prairie voles, an adult male forms a strong pair-bond with one female and helps her care for their offspring. When they first get together, the male and female have sex twenty or more times in a day, which makes them very fond of each other. These animals have high oxytocin levels and large numbers of oxytocin receptors in their brain. If a female’s oxytocin receptors are artificially blocked, she does not pair-bond with a partner. By contrast, a closely related species of vole behaves promiscuously; the males of this species, who mate with many different females, have lower oxytocin levels and fewer oxytocin receptors in their brain. This and other evidence implies that oxytocin plays an important role in pair-bonding, probably by acting on reward centres in the brain.5 One interpretation is that monogamous males become hooked on the pleasure of having sex with their mate. Recent research on humans has shown that spraying oxytocin up someone’s nose makes them more trusting towards other people. We shall return to the subject of trust in the final chapter, in view of its curious relationship with pleasure.
Oxytocin may have some bearing on the anecdotal observation that human drug addicts find it easier to quit their drug habit if they fall in love. Experiments have shown that giving oxytocin to rats or mice reduces their voluntary consumption of heroin and makes them more resistant to becoming tolerant to morphine and alcohol. Oxytocin also alleviates the symptoms of morphine withdrawal and reduces the behavioural effects of cocaine, especially the hyperactivity and stereotyped movements.
Orgasm in human females is usually achieved through direct or indirect stimulation of the clitoris – the only biological structure in the known universe whose sole function is the creation of pleasure. The anatomical structure of the clitoris, as distinct from its much more obvious pleasurable effects, was discovered in the mid-sixteenth century by an Italian professor of anatomy called Matteo Realdo Colombo. His discovery led to him being accused of heresy, blasphemy and Satanism, among other things. A century later, in the more liberated environment of Restoration England, one Jane Sharp felt free to write in her 1671 publication The Midwives Book that the clitoris ‘will stand and fall as the yard [penis] doth and makes women lustful and take delight in copulation’.
The clitoris, for all its awesome pleasure-giving powers, is only part of the story, however. In many women, mechanical stimulation of the vagina or cervix can generate orgasms in the absence of direct clitoral stimulation. This common experience has been confirmed under laboratory conditions in several studies. Many sexologists believe that women are equipped with other anatomical structures that are capable of generating orgasms in their own right. Perhaps the best known of these is the G spot.
According to one version of history, humanity discovered the G spot in 1950. In that year a German gynaecologist called Ernst Gräfenberg published an academic paper in a medical journal, in which he described a ‘distinct erotogenic zone’ on the anterior (front) wall of the vagina. When stimulated, this zone could produce a distinctive type of orgasm. In fact, descriptions of a G-spot-like entity date back much further than the 1950s. References to an erotically sensitive area on the front wall of the vagina can be found in Indian texts dating from the eleventh, thirteenth and sixteenth centuries. These texts also describe how stimulating this zone causes some women to ejaculate a clear liquid. An explicit account of female ejaculation can be found in the work of a seventh-century Indian poet.
Gräfenberg’s research was not of the highest quality; his findings were based on a small sample of women, only some of whom displayed signs of erotic sensitivity in this area. Nonetheless, his observation has been backed up by more solid research. In the early 1980s, sex researchers Beverly Whipple and John D. Perry reported that mechanical stimulation of deep-lying tissue in the front wall of the vagina could induce orgasm. They named this erogenous zone the G spot in honour of Gräfenberg. Their eponymous book became a best-seller, the spot itself became an accepted fact and the rest, as they say, is history. Few writers of sex manuals now doubt the existence of the G spot and an industry has grown around its erotic potential, selling instruction manuals, DVDs and specially shaped G spot vibrators to pleasure-seekers around the world. And yet, the G spot is still not mentioned in most medical textbooks and some scientists are openly sceptical about whether it actually exists. One academic who reviewed the published research likened the G spot to UFOs: much searched for and much discussed, but unverified by objective means. The truth is a little more complex, although still broadly good news.
Evidence from numerous scientific studies leaves little doubt that the front wall of the vagina is erotically sensitive to some degree, and that a majority of women can achieve orgasm with sufficient stimulation of this area, whether manually or during penetrative sex. This was shown, for example, in a laboratory study in which women had the front and back walls of their vagina stimulated. All the women reported that certain areas of their vagina were more erotically sensitive than others, and most of them were able to reach orgasm by stimulating these sensitive zones. Although most women normally achieve orgasm through clitoral stimulation, three out of four women in one study said that vaginal stimulation could also produce orgasm. Most reported that the front wall of their vagina was more sensitive to erotic stimulation than the rear wall. Several other studies reached similar conclusions. That said, there is little solid evidence for the existence of a discrete anatomical structure or erogenous hotspot that corresponds to the ‘G spot’ as it is sometimes portrayed in the popular media.
The fact that the lower front wall of the vagina is to some extent erotically sensitive is unsurprising. Our primate ancestors would presumably have had sex in the rear-entry (‘doggie’) position, which naturally tends to stimulate this part of the vagina. Another possible explanation for at least some ‘G spot orgasms’ is that they are, in fact, indirect clitoral orgasms. Most vaginal orgasms involve at least some indirect stimulation of the clitoris. Rubbing the lower part of the vaginal front wall can have the effect of moving the clitoral hood back and forth across the clitoris, as though the clitoris itself were being massaged. Stimulating the front wall of the vagina can therefore be pleasant and produce orgasms, whether or not that part of the vagina is an erogenous hotspot in its own right. Either way, I see no problem in continuing to call this friendly region the G spot, even if it is neither a spot nor an anatomically distinct organ.
What of the related belief that ‘G spot orgasms’ can bring about
