We are interested in the mechanistic basis for cognitive processes, focusing on the function of hippocampal circuits in learning and memory. To this end, we are developing and applying cutting-edge technology to record and control brain activity using light. This all-optical technology is based on a combination of protein engineering and state-of-the-art microscopes and it allows us to record and manipulate the fine details of neuronal electrical activity at single-cell resolution, in a non-invasive manner. We use this all-optical electrophysiology approach for detailed mechanistic studies of the function and plasticity of hippocampal circuits during various behavioral tasks.