[attach id=537199 size="medium"]Our brain acts as a pleasure centre: many researchers say that sex happens between the ears. Photo: Artwork from Kirsten Woodward, titled Sex on the Brain[/attach]

The core stimuli involved in sex are disgusting. Stimuli such as saliva and sweat are potent contaminants and intrinsically avoided.

By eliciting an overwhelming urge to withdraw from highly disgusting cues, disgust prevents contamination.

So both disgust – to avoid disease and contamination – and sex for pleasure are essential for our survival. They can be considered oppositional forces.

Sexual dysfunction in women mainly takes the form of pain with intercourse (dyspareunia) or an aversion to having anything in the vagina (vaginismus). Research from our lab highlights the potential role of morality or transgression, and disgust in particular, in these penetration-related disorders.

Women with these disorders are characterised by catastrophic pain cognitions (‘my vagina will rapture’, ‘the penis is too large’), strict moral beliefs (‘masturbation is sinful’, ‘anal sex is a perverted activity’), and strong automatic penetration-disgust associations.

Extensions of this work, using techniques to investigate the blood flow in the brains of women, suggest there is significant overlap in the brain regions that respond to pictures of penetration and the regions that respond to disgust cues such as rotten tomatoes.

This is perhaps not surprising given that sexual stimuli such as vaginal fluids and semen are among the strongest disgust elicitors. But despite the disgusting nature of sexual intercourse, people generally still express a good sexual appetite.

Research suggests that this may be because sexual arousal temporarily reduces the disgust-eliciting properties of otherwise disgusting sexual cues.

This makes sense in light of literature indicating that in the ‘heat of the moment’, sex-related risks, such as STDs and pregnancy, become less prominent due to sexual arousal. We would then feel more willing to have sex with people or in circumstances that we would otherwise avoid – if sexual arousal is absent or not sufficient.

Since sexual behaviours imply massive contamination risk, it is sensible that sexual activities such as kissing typically elicit disgust in pre-pubertal children. For most of us, however, disgust towards sexual stimuli subsides and possibly transforms to desire.

Because prolonged contact is a powerful means to reduce disgust, engagement in sexual behaviours can explain why sex-related disgust is hypothesised to decline with increasing age. If such habituation does not occur, sexual disgust may become a chronic symptom; and this disgust could be the disgust that is observed in women with penetration disorders and other sexual problems.

Charmaine Borg is a lecturer and post-doctoral researcher at the Department of Clinical Psychology and Experimental Psychopathology at the University of Groningen (RuG). She has published several articles in the field of emotion research and psychopathology. Her work has featured in many media outlets including Scientific American. Together with Prof. Peter de Jong, she is continuing on her line of research at the same department.

Did you know!

• For the average healthy man there is a staggering 300 million sperm in just a teaspoon of semen.

• That teaspoon contains about seven calories. You burn about 200 calories during 30 minutes of active sex.

• The average amount of time spent kissing for a person in a lifetime is 20,160 minutes. That’s 336 hours, 14 days or two weeks.

• The ancient Egyptians used dried crocodile excrement as a contraceptive. The excrement contains spermicidal properties similar to those used on condoms. One can only wonder how they discovered this.

• Whales are the proud owners of the world’s largest penises. The biggest recorded whale penis was the eight-footer of a killer whale.

For more trivia see: www.um.edu.mt/think

Sound bites

• Male redback spiders are typically eaten after mating with the much larger female. However, male spiders have developed a survival tactic: mating only with females too young to eat them. A study published in the journal Biology Letters has found that some males will avoid becoming a post-coital meal by mating with immature females that are not yet experienced in eating their partners. Researchers conclude that the benefits of immature mating are twofold: not only did it “rarely end in cannibalism”, it also increased male spiders’ chances of successful insemination – and even copulating with a second female as they usually survived their first mating. Though the young females are also not mature enough to conceive immediately, the sperm is stored in their two-sperm storage organs until they reach adulthood, when it fertilises their eggs.

http://www.sciencemag.org/news/2016/09/mating-younger-females-helps-male-spiders-dodge-cannibalism

• Three major genetic studies have been published this week in the same issue of Nature. All three agree that, for the most part, the genomes of contemporary non-African populations show signs of only one expansion of modern humans out of Africa: an event that took place some time after 75,000 years ago.  Two of the studies conclude that, if there were indeed earlier expansions of modern humans out of Africa, they have left little or no genetic trace. The third, however, may have found that ‘trace’. This study, led by Drs Luca Pagani and Toomas Kivisild from the University of Cambridge’s Department of Archaeology and Anthropology, has found a “genetic signature” in present-day Papuans that suggests at least two per cent of their genome originates from an even earlier, and otherwise extinct, dispersal of humans out of Africa.

http://www.cam.ac.uk/research/news/genetic-trace-in-ancient-genomes-suggests-previously-unknown-expansion-out-of-africa