  In bistable systems, the stability of front structures often influences the
dynamics of extended patterns. We show how the combined effect of an
instability to curvature modulations and proximity to a pitchfork front
bifurcation leads to spontaneous nucleation of spiral waves along the front.
This effect is demonstrated by direct simulations of a FitzHugh-Nagumo (FHN)
model and by simulations of order parameter equations for the front velocity
and curvature. Spontaneous spiral-wave nucleation often results in a state of
spatio-temporal disorder involving repeated events of spiral wave nucleation,
domain spliting and spiral wave annihilation.
