Controlling spatiotemporal chaos in excitable media by local biphasic stimulation

Controlling spatiotemporal chaos in excitable media by applying low-amplitude perturbations {\em locally} is of immediate applicability, e.g., in treating ventricular fibrillation, a fatal disturbance in the normal rhythmic functioning of the heart. We look at a mechanism of control by the local application of a series of biphasic pulses, i.e., involving both positive and negative stimulation. This results in faster recovery of the medium, making it possible to overdrive the chaos by generating waves with frequency higher than that possible with only positive pulses. This provides the simplest and most general understanding of the effectiveness of biphasic stimulation in controlling fibrillation and allows designing optimal waveshapes for controlling spatiotemporal chaos.