Did you ever get a brain freeze? Scientists have just discovered the cause (well, they get a bit more detailed than just "eating ice cream and drinking cold drinks, duh!"):
The researchers brought on brain freeze in the lab by having 13 healthy volunteers sip ice water through a straw right up against the roof of their mouth. The volunteers raised their hands when they felt the familiar brain freeze come on, and raised them again once it disappeared.
The researchers monitored the blood flow through their brains using an ultrasoundlike process on the skull. They saw that increased blood flow to the brain through a blood vessel called the anterior cerebral artery, which is located in the middle of the brain behind the eyes. This increase in flow and resulting increase in size in this artery brought on the pain associated with brain freeze.
When the artery constricts, reining in the response to this increased flow, the pain disappears. The dilation, then quick constriction, of this blood vessel may be a type of self-defense for the brain, the researchers suggested.