Nakashima et al. (2015)

Nakashima, S. F.(中嶋智史), Ukezono, M(請園正敏), Nishida, H., Sudo, R.(須藤竜之介) , Takano, Y. (2015).
Receiving of emotional signal of pain from conspecifics in laboratory rats.
Royal Society Open Science.
doi: 10.1098/rsos.140381
Though recent studies have shown that rodents express emotions with their face, whether emotional expression in rodents has a communicative function between conspecifics is still unclear. Here, we demonstrate the ability of visual recognition of emotional expressions in laboratory rats. We found that Long-Evans rats avoid images of pain expressions of conspecifics but not those of neutral expressions. The results indicate that rats use visual emotional signals from conspecifics to adjust their behaviour in an environment to avoid a potentially dangerous place. Therefore, emotional expression in rodents, rather than just a mere ‘expression’ of emotional states, might have a communicative function.