A fundamental property of most visual systems is directional sensitivity, in which objects moving one direction are quickly discriminated from objects moving in an opposite direction. The cellular mechanisms for this property are largely unknown. This collaborative research project brings together the skills of a physiologist and an ultrastructural anatomist in a multidisciplinary approach involving electrophysiology, biochemistry, computational neuroscience and electron microscopy. Using the well-studied visual system of crayfish as a model, this project tests a novel hypothesis that the same excitable membrane channel can integrate excitatory and inhibitory effects of two different neurotransmitter compounds. The technical difficulties give the project a high level of risk, but the potentially very high impact of the results, along with the experience and skills of the PIs, make taking the risk worthwhile. Results will be important beyond simply invertebrate vision, to understanding a fundamental property of visual systems, and to clarifying a cellular mechanism of integration important to all neuroscience as well as to cell physiology.