References and Notes

tion of positive and negative spatiotemporal feedback that is able to accurately direct wave propagation. The control methods presented here also represent potential tools for investigating spa-tiotemporal dynamical systems. Our study has demonstrated that there is a direct pro-portionality between wave trajectory curva-ture and the excitability gradient for a given wave size (24). Control methods also provide a means for probing underlying mechanisms, as demonstrated in studies of homogeneous chemical systems (25, 26). Such techniques are closely related to the relaxation methods developed by Eigen and co-workers (27) for probing chemical kinetics. Spatiotemporal behavior is pervasive in living systems, and control methods offer a promising direction for probing their underlying mechanisms