Neurological and psychiatric disorders afflict over one billion people worldwide, presenting annual costs exceeding $1 trillion. What are the principles of controlling neural circuits, in order to improve their functions and overcome intractable neurological and psychiatric disorders? We have invented cell-type-specific optical neural control technologies, and with them we are seeking to parse out the methods with which to fix activity in aberrant neural circuits, correcting the computational dynamics within, in order to discover new principles of treating neural disease.