Proceed with caution: dynamics of novelty-directed risk assessment behavior in mice*

Mice encountering a novel object initially display a distinctive set of behaviors that have been described as "risk assessment," including slow extensions of their snout toward the object followed by rapid retractions. These behaviors have also been observed in mouse models of anxiety, such as during elevated plus maze tasks, and are proposed to reflect a conflict between exploration and risk avoidance. However, a simple conflict does not explain the asymmetry in the speeds of approach and retreat: why do mice spend more time approaching the object than retreating from it, when spending less time near the object overall could reduce their exposure to risk? Analyzing the snout trajectories of mice exploring a novel object, we test the hypothesis that these behaviors reflect an internal evidence accumulation process, in which mice integrate a subjective "risk" while approaching and retreat when the cumulative "risk" crosses a threshold. We ask whether 1) a feed-forward model can predict retreat timings from preceding trajectories of approach, and 2) including feedback from risk to snout velocity explains the asymmetrical dynamics of "risk assessment".