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Good news for ice-cream lovers: Scientists have solved the mystery of the dreaded gelato-induced brain freeze.

Ice-cream headaches are caused by rapid dilation of a cerebral artery, which floods the brain with blood, causing pain, according to .

The finding debunks the old theory that brain freeze has to do with abrupt temperature changes in the sinuses, .

Researchers at Harvard Medical School pinpointed the source of ice-cream headaches using transcranial Doppler imaging. They looked at cerebral blood flow in patients with acute brain freeze (induced, for the purpose of experiment, with iced water instead of the real stuff) and in a control group drinking tepid water.

Sudden increases in blood flow to the brain cause pain because of the added pressure inside the skull, said the team, who presented their research on Sunday at the Experimental Biology 2012 conference in San Diego.

The mind-numbing pain subsides as soon as the artery constricts – likely to prevent cerebral pressure from reaching the danger zone.

The phenomenon may be part of the brain's defence system, said lead researcher Jorge Serrador, of Harvard Medical School and the War Related Illness and Injury Study Center of the Veterans Affairs New Jersey Health Care System.

Since the brain is sensitive to sudden drops in temperature, dilation of the anterior cerebral artery "might be moving warm blood inside tissue to make sure the brain stays warm," he said in a statement.

The surge of blood could be useful if a person is plunged into an icy lake. But rapid fluctuations in blood flow may also trigger migraines, the researchers said.

Others are skeptical, arguing that migraines are the result of nerve dysfunction.

"Patients [with migraines]experience warning symptoms such as food cravings, frequent yawning, fatigue and neck stiffness a day before the pain, suggesting that migraine is a state of brain dysfunction as opposed to one of vascular [blood flow]dysfunction," Teshamae Monteith, director of the headache program at the University of Miami's Miller School of Medicine,

Drugs that block sudden dilation of cerebral arteries could offer relief for headache sufferers, the Harvard team suggested. But medication would be an extreme treatment for the average dessert lover.

After all, the fleeting agony of brain freeze hasn't deterred generations of chocolate-fudge, French-vanilla or rum-raisin fans.

Are frozen drinks and ice cream worth the pain of brain freeze?