One of the great advantages of being a social animal is the capacity to learn from other members of the pack, but to do this requires cue recognition. Rats automatically respond to certain behaviors from peers but need to be primed by their own experiences to recognize other behaviors. Extrapolating to humans is difficult for such complex behavior, but the work may still have relevance to our own interactions.
Rats need no training to interpret another's fight or flight response to danger. However, only more experienced rats sense danger when a cage-mate freezes. Dr Marta Moita and PhD student Andreia Cruz of Portugal's Champalimaud Centre for the Unknown investigated how and why rats become primed to freeze responses. In Current Biology, Moita and Cruz report that only rats that have experienced what they call “auto-conditioning” react to other rats freezing. This always involves the rats experiencing both pain and immobility.
“For instance, animals that experience a mild foot shock [which is a painful event] and then freeze as a result, learn to recognize freezing in other group members as a threat. But when we prevented the subsequent freezing response by removing the rat from the experimental box immediately after the foot shock, the learning didn't happen," Cruz said in a statement. "We were a bit surprised by the results, because it turns out that the learning mechanism is quite strict.”
Previously, Moita and Cruz showed rats' trigger is others' stillness. Having learned freezing is a response to harm, rats can extrapolate to dangerous situations, and they have enough empathy to recognize the same thing in others.
“When a rat freezes, it stops moving. Which effectively means that it stops generating sound," Moita explained. "We found that this transition from sound to silence can become a social cue by which rats recognize that another group member is freezing."
An auto-conditioned rat recognizes the sudden cessation of sound as a sign another rat senses danger, while a naive rat will not. In PLOS Biology, Moita reports the brain region known as the auditory thalamus identifies this sudden loss of sound. When activity in this area is blocked, rats lose the ability to detect freezing around them.
Sound is perhaps the most common way for animals to alert members of their species to threats. Apparently, rats have re-purposed the mechanism of hearing danger alarms to respond instead to sudden silence.