Optogenetics, or genetically engineering neurons to respond to light, is an important technique for studying how neurons work. However, manipulating individual synapses (gaps between neurons), where signaling transmission occurs, has been challenging until now. Researchers at National Institute of Physiological Sciences, Japan, have now generated a light-activated signaling protein that can help study signaling-related physiological changes in single neurons--a breakthrough that will be valuable for neuroscience.