Migraines are a battle of the sexes that women might prefer not winning. Each year, roughly three times more women than men - up to 18 percent of all women - suffer from the debilitating headaches, as tallied by epidemiological surveys in Europe and the U.S.

A new brain-imaging study may explain the divide: The brains of women with migraines appear to be built differently than those of their male counterparts.

To conduct the study, researchers headed by David Borsook, a neurologist and neurobiologist of Boston Children's Hospital and Harvard Medical School, recruited 44 men and women, half of whom were migraine sufferers.

The women who had migraines rated them as being as intense as the men did, but they tended to find them more unpleasant. Borsook says the distinction is analogous to the loudness of fingernails scratching on a chalkboard versus the torment of hearing the sound.

The team then scanned the brains of the volunteers. The researchers gathered two kinds of data sets, one that captured brain shapes and features, and one that measured brain activity. Female migraine sufferers showed slightly thicker gray matter in two regions: one, the posterior insula, is well-known in pain processing; the other, the precuneus, has been recently linked to migraines but is more widely known as a fundamental brain hub that may house a person's consciousness or sense of self.

The other volunteers, including the male migraine sufferers, did not show this thickening. All of the scans were done when people did not have a migraine.

To figure out what those structural changes meant, lead author Nasim Maleki, a medical physicist at Boston Children's Hospital and Harvard Medical School, returned to the MRI scans of only those men and women with episodic migraines. The team compared brain activity while the volunteers experienced pain - in this case, three 15-second bursts of heat to the hand, spaced 30 seconds apart, generated through a small metal cube, akin to touching a too-hot cup of coffee. In women with migraines, "these thicker areas talk to each other and work together to respond to pain" in a pattern not seen in the men, Maleki says.

When Maleki checked for sex differences in well-defined pain networks, most of the structures that responded stronger in women were part of the emotional network. "In men, the pain comes in, and the brain says 'ouch,' " Maleki says. "In women, the brain says 'OUCHHHHH!' " Overall, the results suggest that "it's not just one area that underlies the sex differences in migraines, but a network of areas, a system that leads to the problem or progression," she said.

The findings, published n this month in the journal Brain, reveal a clearly different brain pattern that may explain why so many more women than men have migraines, said neurologist Peter Goadsby of the University of California-San Francisco, who was not involved in the study.

The greater activation of emotional pain-processing regions in women "could correlate with the greater sense of unpleasantness that is experienced by women with migraine," speculated Todd Schwedt, a neurologist at the Mayo Clinic in Phoenix.