Looming stimuli reliably drive innate, but not learned, defensive responses in rats

Abstract

AbstractThe ability to respond innately to stimuli such as food, water, and threat is crucial for survival as it guarantees the ability to feed, drink, and avoid danger without prior experience. These natural, unconditioned, stimuli can also drive associative learning, such that cues consistently paired with an unconditioned stimulus come to elicit a response. Threat conditioning, an extensively studied form of associative learning, typically uses painful electric shocks that mimics injury as unconditioned stimuli. Whether injury or pain is required for learning, or the threat of injury suffices, remains elusive. An approaching predator produces looming shadows and sounds. Visual looming stimuli elicit strong innate defensive responses such as escape and freezing. Here we ask whether these stimuli can also drive learned freezing or escape responses to a conditioned stimulus. We found that pairing a neutral tone with a looming stimulus failed to drive learned defensive responses, either freezing or escape, in contrast with the robust learned responses when the loom was replaced by shock. The dissociation between the capacity to drive an innate defensive response and to drive threat learning reveals new boundaries for learned defensive responses which will impact our understanding of learning processes and defensive strategies both at the mechanistic and ethological levels.