Versus women with a normal sex drive, premenopausal women who have a lack of interest in sex show distinctive blood flow patterns that activate different parts of the brain.
Researchers at Georgia Regents University recruited 16 female participants to their study. Of these, 6 had a normal sex function and a mean age of 29, while 10 of the women with a mean age of 37 had clear symptoms of "hypoactive sexual desire" - a lack of sexual desire and low sexual arousal.
The study, published in the journal Fertility and Sterility, involved measuring each woman's sexual response to explicit film clips using functional magnetic resonance imaging (MRI) - enabling the researchers to see real-time brain activation in response to a stimulus.
The women who had sexual dysfunction had a higher activation level in the area of the brain called the anterior cingulate gyrus, which triggers emotions including pain, depression and apathy.
The researchers say the brain's amygdala was also activated in the women with sexual dysfunction, a part of the brain central to processing emotion, learning and memory.
Women who had normal sexual function experienced much greater activation in the right thalamus, an area of the brain the researchers say plays a role in sexual arousal by handling sensory and motor stimuli.
The younger women without premenopausal effects on sex drive also experienced activation of the parahippocampal gyrus, the area of the brain that makes and recalls memories, the researchers say. They point out that, interestingly, this area of the brain is usually highly activated in women on hormone therapy after surgical menopause.
Dr. Michael Diamond, chairman of the department of obstetrics and gynecology at the Medical College of Georgia, explains:
"There are site-specific alterations in blood flow in the brains of individuals with hypoactive sexual disorders versus those with normal sexual function.
This tells me there is a physiologic means of assessing hypoactive sexual desire and that as we move forward with therapeutics - whether it's counseling or medications - we can look to see whether changes occur in those regions."
Dr. Diamond says that up to 20% of women may have this type of sexual dysfunction. But while there are plenty of options for men, such as the drug Viagra (sildenafil) for male impotence, there is no treatment given official approval by the US Food and Drug Administration (FDA) for women with hypoactive sexual desire.
Dr. Diamond said that he plans to use these latest results to to assess a larger group of women, and use brain blood flow patterns to assess therapies.