How are transient experiences converted into long-lasting memories? How do experiences modify behaviors? How do similar experiences elicit drastically different behavioral responses in the healthy and disease states? The key to answering these important questions is to understand how sensory information is processed and stored in the brain. My research aims to address these questions at the molecular and cellular level, by exploring the mechanisms by which experiences are coupled to synaptic modifications of neural circuits that lead to long-term behavioral changes. This is made possible by combining a very wide range of experimental techniques: generating molecular tools to genetically identify the ensembles of neurons in the brain that are activated by a specific sensory and behavioral experience, detecting the learning-induced synaptic changes on the ensemble neurons, dissecting the molecular pathways responsible for the synaptic modulation, and understanding how the ensemble neurons contribute to the neural computations underlying learning and memory. My talk will focus on the progress we have made in understanding the mechanisms underlying contextual memory formation in the hippocampus.