Abstract
To survive predation, animals must be able to detect and appropriately respond to predator threats in their environment. Such defensive behaviors are thought to utilize hard-wired neural circuits for threat detection, sensorimotor integration, and execution of ethologically-relevant behaviors. Despite being hard-wired, defensive behaviors (i.e. fear responses) are not fixed, but rather show remarkable flexibility, suggesting that extrinsic factors such as threat history, environmental contexts, and physiological state may alter innate defensive behavioral responses. The goal of the present study was to examine how extrinsic and intrinsic factors influence innate defensive behaviors in response to visual threats. In the absence of a protective shelter, our results indicate that mice showed robust freezing behavior following both looming (proximal) and sweeping (distal) threats, with increased behavioral vigor in response to looming stimuli, which represent a higher threat imminence. Repeated presentation of looming or sweeping stimuli at short inter-trial intervals resulted in robust habituation of freezing, which was accelerated at longer inter-trial intervals, regardless of contextual cues. Finally, prior stress history such as acute foot shock further disrupted innate freezing habituation, resulting in a delayed habituation phenotype, consistent with a heightened fear state. Together, our results indicate that extrinsic factors such as threat history, environmental familiarity, and stressors have robust and diverse effects on defensive behaviors, highlighting the behavioral flexibility in how mice respond to predator threats.