"A mouse's pain face is exactly the same as the human pain face, at least with respect to those features that they have in common (tightening of the eyes, bulging of the nose and bulging of the cheeks)," and humans and mice use the same muscles to create those signals, Mogil said. Mice also have two expressions that are "mouse-specific" (movement of the whiskers and ears,) he added.
Mogil teamed up with a fellow pain expert, Kenneth Craig of the University of British Columbia in Vancouver, to come up with a "mouse grimace scale" that veterinarians and researchers can use to measure pain in lab mice. That should be useful in the search for pain medications, and it should help ensure humane treatment of laboratory animals.
The pain induced in the mice used in this study "ranges from dipping the tail in hot water to the inflammation of body parts," Mogil said. "If you want to study pain you have to impose some pain, and this is very mild pain."
It was enough, however, for Craig's team to isolate photos of Mogil's mice that showed various levels of pain, and thus create a scale that requires only a little practice to master. It only took an hour of training for participants in the study to accurately determine the level of pain (from none to severe) 75 percent of the time, using the mouse grimace scale. More training, and better videos, boosted that success rate to 97 percent.
Mogil expects attacks from animal-rights activists for inflicting even modest pain on lab mice, but he argues that the study should have "positive implications for pain in laboratory mice," in that researchers will be able to tell just how much pain the mouse is experiencing and treat it accordingly.
What is perhaps most surprising in all of this is that it took so long to come up with a way to document pain just through facial expressions.
There have been some studies of various animals and how they express emotions, mostly fear, because that's easier to create than a feeling of happiness. Mogil described the lack of research as "shocking."
So how did he manage to pull it off, at least for mice and pain?
"I have an advantage over most pain researchers in that I teach at an undergraduate institution, not a medical school, and because of that I have access to very high quality and very free labor" in the form of undergraduates, he said. "This method is quite labor intensive. You have to take video and then you have to isolate still photographs and that takes a long time."
Now, if they can just figure out how to make a mouse smile.