Creating stable memories is critical for survival. An animal relies on past learning to navigate its environment, avoid dangerous situations, and find needed resources. Because the environment is dynamic, stable memories must be updated with new information to enable responses to changing threats (a specific danger) and rewards (such as food and water).The brain circuits involved in memory and learning require both stability and flexibility. Using in vivo calcium imaging, immediate-early gene tagging, and chemogenetics, we demonstrate how the dynamic activity of neural ensembles supports the “tug of war” between memory stability and flexibility in a mouse model.