The Progressive Era. During the period known as the Progressive Era (1890s to about 1920) the U.S. government became increasingly activist in both domestic and foreign policy.
One possible link between brain freeze and other headaches is local changes in brain blood flow. If further research confirms all these types of headaches are caused by blood flow changes, new drugs that block widening of the blood vessels - called vasodilation - could improve treatment for sufferers.
International Headache Society gives detailed classification of brain freeze. Pain is caused by opening and closing of blood vessels that flow past the throat to the brain, normally when cold food or liquid is consumed quickly. Official name for 'ice-cream headache' is sphenopalatine ganglioneuralgia.