Scientists have uncovered a trio of genes tied to migraine headaches, including one in which the link is exclusive to women

Some invent a headache while others claim they are too tired.

But scientists believe there may be a medical reason why women give their husbands excuses for not wanting to make love.

They have discovered that the brains of females with a low libido behave completely differently to those with healthy sex drives.

Those with a low libido do not have the same rush of blood to certain brain cells during moments of passion, which could explain why they don’t enjoy it.

The US scientists compared the brains of 19 women diagnosed with a form of low libido known as hypoactive sexual desire disorder with the brains of seven women with a normal sex drive.

The team, from Wayne State University in Detroit, asked them to watch erotic films and then a blank screen while they examined their brains using MRI scans.

Their study, which is being presented today at the American Society for Reproductive Medicine’s annual conference in Denver, Colorado, found that during the sex scenes, the women with a normal sex drive had an increased flow of blood to parts of their brain.

But those with low libido did not have any increase in blood flow.

Some doctors claim that low libido is a complaint invented by drugs firms to cash in on female versions of Viagra.

But Dr Michael Diamond, who carried out the latest research, said: Being able to identify physiological changes, to me provides significant evidence that it’s a true disorder as opposed to a societal construct. - Daily Mail