Lecture, three hours. Animals face changing threats in nature, and have evolved the ability to dynamically alter behavior to minimize threat exposure and increase the probability of survival. Threats of different modalities and intensities can provoke distinct defensive behaviors, such as freezing or escape. Neural pathways involved in generating and suppressing these behaviors may differ depending on the type of threat, even when considering the same defensive behavior. For example, freezing caused by a fear conditioned tone and by a live predator are controlled by overlapping, but separate circuits. Introduction to the main types of techniques that are covered in the papers that are discussed. These papers demonstrate how and when distinct neural pathways are mobilized to generate the appropriate defensive behavior. Papers cover recent rodent experiments using state-of-the-art methods with high temporal, genetic, and anatomical specificity to investigate the circuits underlying defensive behaviors. May be repeated once for credit. P/NP or letter grading.