Sex on the brain: What turns women on, mapped out

It's what women have been telling men for decades: stimulating the vagina is not the same as stimulating the clitoris. Now brain scan data has added weight to their argument.

The precise locations that correspond to the vagina, cervix and female nipples on the brain's sensory cortex have been mapped for the first time, proving that vaginal stimulation activates different brain regions to stimulation of the clitoris. The study also found a direct link between the nipples and the genitals, which may explain why some women can orgasm through nipple stimulation alone. The discoveries could ultimately help women who have suffered nerve damage in childbirth or disease.

The sensory cortex is a strip of brain tissue positioned roughly under where the band between a pair of headphones sits. Across it, neurons linked to different body parts exchange information about the sensory information feeding into them. This is often depicted as the "sensory homunculus", a distorted image of a man stretched across the brain, with his genitals lying next to his feet (click here). The size of the body's parts show how much of the brain is dedicated to processing the sensory information from each body part.

The diagram was first published in 1951 after experiments conducted during brain surgery performed while the patients were conscious: the surgeon electrically stimulated different regions of the patients' brains and the patients reported the parts of their bodies in which they felt sensation as a result. But all the subjects were men. Until recently, the position of female genitalia on the homunculus had only been guessed at.

This changed last year when a team led by Lars Michels at University Children's Hospital in Zurich, Switzerland, used functional magnetic resonance imaging to confirm that the position of the clitoris on the homunculus was in approximately the same position as the penis in men. Barry Komisaruk at Rutgers University in Newark, New Jersey, and his colleagues have now used the same method to map the position of the clitoris, vagina and cervix on the sensory cortex as women stimulated themselves.

There, there and there

"This is hard proof that there is a big difference between stimulating those different regions," says Stuart Brody of the University of the West of Scotland in Paisley, UK, one of the researchers in the study.

Some have argued that women who derive pleasure from vaginal stimulation do so because their clitoris is being indirectly stimulated, but the current findings contradict this. "They support the reports of women that they experience orgasm from various forms of stimulation," says Beverly Whipple, also of Rutgers University, who was not involved in the current study.

It's the nipples, stupid

Komisaruk also checked what happened when women's nipples were stimulated, and was surprised to find that in addition to the chest area of the cortex lighting up, the genital area was also activated. "When I tell my male neuroscientist colleagues about this, they say: 'Wow, that's an exception to the classical homunculus,'" he says. "But when I tell the women they say: 'Well, yeah?'" It may help explain why a lot of women claim that nipple stimulation is erotic, he adds.

The next step is to map what other areas of the brain light up in response to clitoral and vaginal stimulation. Komisaruk would also like to see what happens when the area that supposedly contains the G-spot is stimulated, as women in the current study just stimulated the front wall of the vagina generally.

The findings could also help women who have suffered nerve damage in childbirth or because of diseases like diabetes. Michels has preliminary evidence that stimulating the clitoral nerve can improve symptoms of urinary incontinence, but says a proper understanding of how the nerve maps to the brain is needed to translate this into effective treatment.

Meanwhile, Komisaruk says that nipple stimulation could enhance genital sensation in women with nerve damage. "It could be a supplement for experiencing orgasm," he says.

Journal reference: Journal of Sexual Medicine, DOI: 10.1111/j.1743-6109.2011.02388.x