Gil Bub McGill University | Department of Physiology Title: Optical Control of Excitation Waves in A Biological Excitable Medium Abstract: Macroscopic excitation waves are found in a diverse range of settings including chemical reactions and the heart and brain. In the case of living biological tissue, the spatiotemporal patterns formed by these excitation waves are different in healthy and diseased states. Current electrical and pharmacological methods for wave modulation lack the spatiotemporal precision needed to control these patterns. Optical methods have the potential to overcome these limitations, but until recently have only been demonstrated in simple systems. Here I discuss results using a new dye-free optical imaging modality with optogenetic actuation to achieve dynamic control of cardiac excitation waves. Illumination with patterned light is demonstrated to optically control the direction, speed, and spiral chirality of such waves in cardiac tissue. This all-optical approach offers a new experimental platform for the study and control of pattern formation in complex biological excitable systems.