Have you ever wondered why you get "brain freeze" when you eat something cold such as ice cream or a milkshake? That sudden pain in your forehead is known in medicine as sphenopalatine ganglioneuralgia, and occurs because the abrupt change in temperature in the tissue at the roof of your mouth causes blood vessels to quickly swell in an effort to warm the area back up.
Image by Andy Reid
About.com's Guide to Chemistry, Anne Marie Helmenstine, Ph.D., explains, "The dilation of the blood vessels triggers pain receptors, which release pain-causing prostaglandins, increase sensitivity to further pain, and produce inflammation while sending signals through the trigeminal nerve to alert the brain to the problem. Because the trigeminal nerve also senses facial pain, the brain interprets the pain signal as coming from the forehead. This is called 'referred pain' since the cause of the pain is in a different location from where you feel it."
Check out this brief video in which Dr. Charlotte Grayson explains the phenomenon and offers a few tips on how to avoid brain freeze. Why Do You Get Brain Freeze?