The nervous system is an outstanding computing center that controls all the activities of an individual. Many neurons in this complex network transmit information from one to the others at the synapse by releasing neurotransmitters that store in synaptic vesicles. Traditionally, scientists monitor the convey of signals by electrophysiological recording, but over the past decade, optical approaches have becoming feasible to study the neuron activity with even a better spatial resolution. The goal of this project is to develop a novel fluorescent probe that can resolve neuronal activity using genetic amenable optical approaches in the living fly brain. By modifying the so-called GFP reconstitution across synaptic partners (GRASP) technique, we have developed a set of probes to detect functional connectivity of olfactory and visual circuits in the fly brain.