Noise and complexity in three-dimensional excitable media

We investigate the effects of external noise on pattern formation in a thre e-dimensional, pulse coupled excitable medium. It is found that for weak to moderate coupling between the cells, simple scroll waves evolve into compl ex patterns. The increase of the lengths of vortex lines quantifies the inc reasing complexity of the patterns. Noise nucleates patterns in the bulk of the medium via the formation of small vortex rings that subsequently expan d for weak to moderate coupling.