Distress of mice induces approach behavior but has an aversive property for conspecifics

In the first experiment, approach/avoidance behavior of mice to a restrained cage mate was examined. The mice explored the restrained mates but they did not stay longer at the restrained mates in comparison to free moving mates. Conditioned Place Preference (CPP) training in the presence of a restrained mate did not result in preference or aversion to the compartment associated with the restrained mates. A second experiment used formalin injection to a hind paw of a cage mate, instead of restraint. Mice stayed longer at the cage mate injected with the formalin in comparison to intact mates. However, CPP with formalin-injected mates caused conditioned aversion to the compartment associated with the formalin-injected mate. Thus, distress in mice induced short-term approach behavior in conspecifics but also had an aversive property.

► Cognition of distress of conspecifics gives important information to others, because it can be signal of their own danger.
► Therefore, distress of others may cause explanatory or curiosity behavior in conspecifics.
► Other aspect of the distress of others should be aversive one.
► Several studies demonstrated such aversion of conspecific distress.
► The present experiments separate the two aspects experimentally and the results contribute to understanding of evolutionary origin of human emotion.