Control of spiral waves in excitable media

The propagation of spiral-shaped excitation waves is a prominent example of self-organization in nonequilibrium systems. The properties of these waves are studied in a chemical model system--the Belousov-Zhabotinsky (BZ) reaction--and in various biological excitable media such as heart or neuronal tissue. An important aspect lies in finding tools for external control of these waves. A light-sensitive variant of the BZ reaction has proven to be a suitable system for investigating local and global control by means of a time-dependent uniform illumination. A local feedback control, in which short light pulses are applied at instants corresponding to the passage of a wave front through a measuring point, results in a drift of the spiral center along a discrete set of stable circular orbits. In a confined-domain control, where the illumination intensity is taken to be proportional to the average wave activity observed in a circular domain of the reaction layer, the stabilization and destabilization of spiral wave trajectories are demonstrated. The presented methods could be useful for the control of biological excitation waves.