  In nature, excitable reaction-diffusion systems found in diverse settings (e.g. chemical reactions, metal rust, yeast, amoeba, heart, brain) generate geometrically similar macroscopic waves(1,2). For the heart and brain, the spatiotemporal patterns formed by these excitation waves separate healthy from diseased states(1-3). Current electrical and pharmacological therapies for bioelectric disorders often lack the necessary spatiotemporal precision needed to control these patterns. Optical methodologies have the potential to overcome these limitations, but have only been demonstrated in simple systems, e.g. the Belousov-Zhabotinsky (BZ) chemical reaction4. Here we combine novel dye-free optical imaging with optogenetic actuation for dynamic control of cardiac excitation waves. We leverage patterned light to optically control emergent macroscopic properties of cardiac tissue: wave direction, wave speed, and spiral wave chirality. This all-optical approach offers a fundamentally new experimental platform for the study and control of pattern formation in complex biological excitable systems. 
Optical control of waves in a cardiac excitable medium