Front propagation and pattern formation in anisotropic bistable media

The effects of diffusion anisotropy on pattern formation in bistable media are studied using a FitzHugh-Nagumo reaction-diffusion model. A relation be tween the normal velocity of a front and its curvature is derived and used to identify distinct spatiotemporal patterns induced by the diffusion aniso tropy. In a wide parameter range anisotropy is found to have an ordering ef fect: initial patterns evolve into stationary or breathing periodic stripes parallel to one of the principal axes. In a different parameter range, ani sotropy is found to induce spatiotemporal chaos confined to one space dimen sion, a state we term "stratified chaos."