Spiral waves, which travel along expanding circular paths, are a feature of many physical, biological, and chemical systems. Some of their most dramatic manifestations are in the human body. For example, spiral waves can occur on the tongue in migratory glossitis, a condition in which the papillae—the bumps that cover the upper part of the tongue and house the taste buds—are missing due to inflammation of the mucous membrane, and the patterns of smooth patches can propagate as spirals. They also occur in the cortex of the brain, where they can lead to epilepsy.
The most dangerous spiral waves occur in the heart (see the Physics Today articles by Leon Glass, August 1996, page 40, and Alain Karma and Robert Gilmour, March 2007, page 51). There, spiral waves of electrical activity (see figure 1) can induce tachycardia, an anomalously high resting heart rate, as the spiral propagation...
