Spreading depression, the most likely cause of migraine aura and pain, propagates at the unique speed of 3 millimeters a minute. The causes for this brain event are beginning to be understood. The fact that the brain of migraineurs is more excitable than normal takes on added importance when one considers a fascinating chemical reaction that can be demonstrated in a Petri dish. The reaction is called a Belousov-Zhabotinsky reaction. When special chemicals are mixed in a dish and made sufficiently excitable at a triggering point, a slowly propagating chemical oscillation is created — much like what can happen when increased brain activity from a triggering event evoke a migraine. As a result, recurrent waves begin to travel from the stimulus point, like waves from the sea coming ashore as shown in the video. Remarkably these waves travel at three millimeters / minute, just like spreading depression. (This video was created with the assistance of Ms. Jane Babiarz from the University of Chicago.)