Rats exchange information about danger in a reciprocal fashion, and this information transfer is at least partially mediated by a brain region called the anterior cingulate cortex, according to a study published December 5 in the open-access journal PLOS Biology by Christian Keysers of the Netherlands Institute for Neuroscience and the University of Amsterdam, and colleagues.

The ability to anticipate threats and deploy defensive responses appropriately is key to survival. Rodents have evolved mechanisms to use the response of conspecifics to more selectively deploy defensive behavior in anticipation of danger. Until now, social transmission of freezing -- a behavioral manifestation of fear in rodents -- was conceived of as a one-way phenomenon in which an observer perceives the fear of another. In the new study, Keysers and colleagues systematically quantified the transfer of information between rats in the context of danger, and how this information transfer is affected by deactivation of the anterior cingulate cortex -- a brain region that contains emotional mirror neurons in rodents. Unlike more traditional methods that focus on one direction of information flow at a time, the methods the researchers introduced allowed them to capture social influences in both directions in the same paradigm. The paradigm they developed in the lab involves a shock-experienced observer rat interacting through a perforated transparent divider with another rat receiving footshocks.

The results suggest that rats exchange information about danger in both directions; how the observer reacts to the other rat's distress also influences how the rat receiving footshocks responds to the danger. This is true to a similar extent across highly familiar and entirely unfamiliar rats, but is stronger in animals pre-exposed to shocks. The effect of pre-exposure suggests that information transfer about danger is not entirely inborn; instead, part of the information transfer depends on some form of learning, similar to cross-species transfer of danger information via eavesdropping. Moreover, deactivating the anterior cingulate of observers reduces freezing in the observers and in the rats receiving the shocks. Taken together, the findings suggest that coupling of freezing across rats could enhance the efficient detection of danger in a group, similar to cross-species eavesdropping.

"What we observed, was striking," said Christian Keysers. "Without the region that humans use to empathize, the rats were no longer sensitive to the distress of a fellow rat. Our sensitivity to the emotions of others is thus perhaps more similar to that of the rat than many may have thought."

They go on to say, "What our data suggest, is that an observer shares the emotions of others because it enables the observer to prepare for danger. It's not about helping the victim, but about avoiding to become a victim yourself."