We know someone is in pain just by looking at their face. Winced eyes, grimacing smile. We recognize it immediately. But can we see pain in nonhuman faces?
Well, recent research published in the journal Nature Methods shows that mice show the facial expressions of pain just like humans do.
Scientists injected mice with inflammatory drugs, which led to pain similar to a headache or a swollen finger. Then they videotaped the mice and had the video images analyzed by expert facial-expression decoders. The researchers scored five distinct mouse pain expressions. Eyes close and squint, nose bulges, cheeks bulge and mice also pull back their little round ears and move their whiskers. All of this led to the creation of a "mouse grimace scale".
It's a bit surprising that this is the first study of facial expressions of pain in nonhumans. Prior to this, scientists detected pain in mice from reflex reactions, like heat to the tail makes the tail flick.
Next up is to see whether this scale can translate to other mammals. Pain research depends on mouse studies, so having a method to measure a mouse's pain will help researchers understand chronic and spontaneous pain in humans.
This research also opens up the possibility of studying mouse social behavior, like to see if mice respond to the facial cues of other mice. Won't that be interesting—to see if or how a mouse consoles another mouse in pain?