Your brain mediates everything you sense, feel, think, and do -- and acts as your ultimate 'neuromedia' interface to the world. A challenge for humanity is to understand the brain at a level of abstraction that enables the engineering of its function -- so that it becomes possible to understand the brain in concrete terms, and also to effectively and precisely treat intractable brain disorders. We are inventing new tools for analyzing and engineering brain circuits. For example, we have devised 'optogenetic' tools, which enable the activation and silencing of neural circuit elements with light, to understand their causal contribution to normal and pathological neural computations, as well as to support the discovery and repair of neural circuit targets in a therapeutic context. We are using our inventions to enable systematic approaches to neuroscience, revealing how neural circuits operate to generate behavior, and empowering new therapeutic strategies for neurological and psychiatric disorders.