Noise-induced spiral dynamics in excitable media

We report the existence of complex spiral dynamics induced by external nois e in a simple two-dimensional model of excitable media! with local dynamics of the FitzHugh-Nagumo type. Different dynamical regimes can be observed, depending on the value of the activator diffusion, including complex states resembling deterministic spiral turbulence, and spiral meandering. The com plex dynamical behavior is seen to be driven by spiral breakup. The complex ity of these noise-induced states can be characterized by the number and si ze distribution of coherent space-time clusters. In particular, the turbule nt-like regime is characterized by a cluster-size distribution that display s power law scaling.