Women with a low sex drive could now have a scientific explanation for their lack of desire after experts found their brains behave differently.
Those with a low libido have different patterns of brain activity to women with a healthy sex drive, according to a new study.
Experts asked women to watch a series of videos, including erotic scenes, and measured their brain's response using MRI scans.
Certain areas of the brain that normally light up when processing information about sex failed to do so in women with low libido.
Researcher Dr Michael Diamond, from Wayne State University in Detroit, said the findings offered "significant evidence" that persistent low sex drive - known as hypoactive sexual desire disorder (HSDD) - is a genuine physiological disorder and not made up.
There has long been controversy over whether HSDD is a real medical condition or a variation of normal human behaviour.
He said: "Us being able to identify physiological changes, to me provides significant evidence that it's a true disorder as opposed to a societal construct.
"The study provides a physical basis suggesting that it is a true physiological disorder."
The research, which is being presented at the American Society for Reproductive Medicine (ASRM) conference in Denver, involved 19 pre-menopausal women with clinically-diagnosed HSDD and seven women with normal sexual function.
The women were asked to watch television for half an hour, during which time a blank blue screen, everyday programmes and erotic videos were alternated every minute. Brain scans showed differences in how the women's brains interpreted the sexual stimulus.