Sexual desire on a brain scan

Researchers have found a link between sexual desire in women and the activation of certain brain regions.

Previous studies of factors affecting sexual performance have largely focused on men, and on the physiology of the body rather than the brain. But the brain, rather than peripheral organs, may play the key role in female sexual dysfunction, the researchers write.

More than 40 percent of women ages 18-59 are estimated to experience sexual dysfunction, with lack of sexual interest — hypoactive sexual desire disorder, or HSDD — being the most commonly reported complaint.

How the study was conducted
The researchers compared brain-activation patterns of women who have HSDD with those who don't. Sixteen women diagnosed with HSDD, along with 20 normal control subjects, took part in the study. All subjects identified themselves as heterosexual.

The women were shown erotic video segments interspersed among footage of female sporting events. These segments were separated by intervening tranquil sequences of such subjects as flowers, mountains or ocean waves to bring the women's brains to a resting state between more-active segments.

Their brain activity was monitored by functional magnetic-resonance imaging, which allows the activity of different brain regions to be assessed in real time. The women also reported their subjective levels of sexual arousal throughout the viewing.

Meanwhile, the researchers also collected objective measurements of the women's level of genital arousal.

Notable differences
Activity patterns throughout most of the brain were more or less identical among the HSDD and normal groups, but with a few notable exceptions. There was a bigger jump in relative activity in three brain areas of HSDD women — the medial frontal gyrus, right inferior frontal gyrus and bilateral putamen — compared with the control subjects when shown the erotic clips.

In another brain area — the bilateral entorhinal cortex — the opposite effect occurred.

This finding establishes specific locations in the brain where activity in women with HSDD is altered in comparison with women not reporting this problem, the researchers wrote.

Tied to attention
Two of the brain areas where the HSDD women had increased activity (the medial frontal gyrus and right inferior frontal gyrus) have been previously associated with, respectively, heightened attention to one's own and others' mental states, and suppression of one's emotional response.

The research suggests that increased attention to one's own responses to erotic stimuli plays some part in the sexual dysfunction.

The researchers speculated that the increased activation in the entorhinal cortex observed in the control subjects may correlate with an improved ability among women with no sexual dysfunction, compared with HSDD women, to lay down emotional memories related to sexual events.

They emphasised however, that correlation is not cause and effect. "The study could be showing how paying too much attention causes inhibition of sexual desire — or how the lack of desire in a sexually charged situation causes heightened self-consciousness," they explained.

"The results of this study provide yet another valuable tool for understanding the complexity of female sexual function as it relates to desire," said co-author Dr Leah Millheiser, clinical assistant professor of obstetrics and gynaecology and director of the Female Sexual Medicine Program at Stanford Hospital & Clinics. "The next step is to translate this information into the clinical realm, specifically as it relates to cognitive and pharmacotherapeutic approaches."

The study was published in the journal Neuroscience. - (EurekAlert, March 2009)