These simple learned associations guide our behavioral response to the environmental stimuli that continually surround us. Associative learning also provides a means whereby stimuli in the environment come to regulate our emotional responses and to strongly bias our decision-making. Thus we seek to define the behavioral and neural mechanisms for the acquisition of reward-based associations. In addition, we are interested in the neural systems that control expression of stimulus-guided behavior after learning. Because associative learning mechanisms contribute to pathological behaviors such as drug and alcohol addiction and overeating, an additional focus of our work is translational. In these studies, we apply our findings on associative learning to understand better how drug- and alcohol-associated stimuli contribute to relapse. To realize our basic and translational goals, we use well-defined animal models of learning and addiction in concert with in vivo electrophysiological measurement and optogenetic manipulation of neuronal populations in specific brain regions and circuits.