Organizing centers in a cellular excitable medium

Excitable media provide much of the subject-matter of physiology, especially of electrophysiology. We simulate excitability in a cubical three-dimensional grid of discrete cells. Topologically distinct organizing centers for self-sustaining rhythmic activity (at period 4) arise from suitable initial conditions. Two are shown: the scroll ring and the linked pair of twisted scroll rings. The first has already been observed in a chemically excitable reagent and possibly in heart muscle; the second, and others of a predicted “periodic table of organizing centers”, remain to be observed outside computers.