For years, one universal scientific phenomenon has baffled scientists and lovers of ice cold sodas and slushies. Why do we get a raging headache when we drink a cold beverage way too fast?

Now science has found the answer.

Scientists from the Harvard Medical School finally discovered the cause of this strange and supremely painful phenomenon, commonly called "brain freeze." They conducted a study by giving ice cold water to 13 volunteers and had them drink the water through a straw while aiming it directly at the roof of their mouths. They were told to raise their hands when their heads started to ache.

Researchers monitored the volunteers' blood flow through their brains with an ultrasound. They found that increased blood flow through the anterior cerebral artery, located in the middle of the brain behind the eyes, caused it to swell up suddenly as the temperature dropped. This causes the pain we know as "brain freeze."

The scientists described this act as a "defensive mechanism" for the brain. Since the temperature drops and the brain requires warmth to work, this widening of the artery provides a way to move the coldness along quicker and return the artery to its normal temperature. So the next time you get a blindly headache after downing a milkshake, know that's just your brain's way of protecting itself.

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