In the basic excitable medium illustrated here, a cell has three states, namely, ready, firing, and recovering; the firing of a cell is stimulated by the firing of adjacent cells. Firing threshold and recovery time are adjustable parameters. Excitable media have long provided models for population dynamics, chemical reactions, brain activity, etc. Similar models may help us harness for useful computing tasks the raw pre-computational capabilities of large arrays of microscopic active elements (quantum dot arrays).