Have you ever wanted to know whether a mouse is in pain?
Of course you have. And now you can, thanks to Langford et al's paper Coding of facial expressions of pain in the laboratory mouse.
It turns out that mice, just like people, display a distinctive "Ouch!" facial expression when they're suffering acute pain. It consists of narrowing of the eyes, bulging nose and cheeks, ears pulled back, and whiskers either pulled back or forwards.
With the help of a high-definition video camera and a little training, you can reliably and accurately tell how much pain a mouse is feeling. It works for most kinds of mouse pain, although it's not seen in either extremely brief or very long-term pain.
Langford et al tried it out on mice with a certain genetic mutation, which causes severe migraines in humans. These mice displayed the pain face even in the absence of external painful stimuli, showing that they were suffering internally. A migraine drug was able to stop the pain.
Finally, lesions to a part of the brain called the anterior insula stopped mice from expressing their pain. This is exactly what happens in people as well, suggesting that our displays of suffering are an evolutionary ancient mechanism. Of course this kind of study can't prove that animals consciously feel pain in the same way that we do, but I see no reason to doubt it: we feel pain as a result of neural activity, and mammals have exactly the same brain systems.
Langford, D., Bailey, A., Chanda, M., Clarke, S., Drummond, T., Echols, S., Glick, S., Ingrao, J., Klassen-Ross, T., LaCroix-Fralish, M., Matsumiya, L., Sorge, R., Sotocinal, S., Tabaka, J., Wong, D., van den Maagdenberg, A., Ferrari, M., Craig, K., & Mogil, J. (2010). Coding of facial expressions of pain in the laboratory mouse Nature Methods, 7 (6), 447-449 DOI: 10.1038/nmeth.1455