Scroll breakup in a three-dimensional excitable medium.

We show that a scroll wave in a homogeneous three-dimensional (3D) excitable medium can spontaneously break up into an irregular spatial pattern. This occurs in a FitzHugh-Nagumo model with modified dynamics of the slow variable (shortened relative refractory period of the excitable medium). The mechanism of the scroll breakup in 3D is similar to the mechanism of the spiral breakup in 2D and is associated with the instability of wave propagation under high frequency forcing. \textcopyright{} 1996 The American Physical Society.