Silence resulting from the cessation of movement signals danger

Abstract

Summary Most of what we know about the neural basis of fear has been unravelled by studies using associative fear learning [1]. However, many animal species are able to use social cues to recognize threats [2,3], a defence mechanism that may be less costly than learning from self-experience. Most studies in the field have focused on species-specific signals, such as alarm calls or pheromones, remaining unclear whether more generic cues can mediate this process. Here we report that rats perceive the cessation of movement-evoked sound as a signal of danger and its resumption as a signal of safety. To study transmission of fear between rats we assessed the behavior of an observer while witnessing a demonstrator cage-mate display fear responses. Having tested a multitude of cues, we found that observer rats respond to an auditory cue which signals the sudden immobility of the demonstrator rat — the cessation of the sound of motion. As freezing is a pervasive fear response in animals [4,5], silence may constitute a truly public cue used by a variety of animals in the ecosystem to detect impeding danger.