When a person gets a sudden headache after indulging in cold desserts, such as ice cream, everyone would say it is only "brain freeze" and it will soon pass. Now Harvard scientists have looked deeper and found an explanation, Daily Mail reported.

A team from Harvard Medical School tracked blood flow to the brain as study participants drank ice-cold water to observe developments in the brain from the time of taking in the cold water to the point of swallowing.

The study is meant to pinpoint how "ice cream headaches" or brain freeze begin inside one's body, the findings of which could lead to developments of new treatments for headaches, said researcher Jorge Serrador.

The participants observed their pain started when their anterior cerebral artery (situated somewhere far behind the eyes) opened up and filled the brain with blood. As the artery constricted, the pain also subsided.

Mr Serrador said his theory is that the rush of blood is the brain's defence mechanism against abnormal temperature.

"The brain needs to be working all the time... It's fairly sensitive to temperature, so [the artery] might be moving blood to make sure the brain stays warm," he said.

He noted the opening up of the artery might be raising pressure in the skull, which causes pain. In a sequential defence process, the artery constricts to stop the pressure, hence, the pain subsides after a while.

Findings of the study were presented to the Experimental Biology conference.