Rapid innate defensive responses of mice to looming visual stimuli.

Much of brain science is concerned with understanding the neural circuits that underlie specific behaviors. While the mouse has become a favorite experimental subject, the behaviors of this species are still poorly explored. For example, the mouse retina, like that of other mammals, contains ∼20 different circuits that compute distinct features of the visual scene [1, 2]. By comparison, only a handful of innate visual behaviors are known in this species--the pupil reflex [3], phototaxis [4], the optomotor response [5], and the cliff response [6]--two of which are simple reflexes that require little visual processing. We explored the behavior of mice under a visual display that simulates an approaching object, which causes defensive reactions in some other species [7, 8]. We show that mice respond to this stimulus either by initiating escape within a second or by freezing for an extended period. The probability of these defensive behaviors is strongly dependent on the parameters of the visual stimulus. Directed experiments identify candidate retinal circuits underlying the behavior and lead the way into detailed study of these neural pathways. This response is a new addition to the repertoire of innate defensive behaviors in the mouse that allows the detection and avoidance of aerial predators.