Mapping facial expressions in mice as an indicator of pain

In a collaboration between UBC and McGill researchers, a study was very recently published in Nature Methods which looks to quantify pain based on facial expressions in mice. The study has since been popularly named the “Mouse Grimace Study” in popular media, such as the local Vancouver Sun and online at Science Daily.

I can’t seem to get access to the full journal article at the moment, but from what I’ve read, the study investigators injected mice with solutions containing varying levels of irritant. They suggest that the pain level is somewhat similar to a headache. I’m a bit skeptical at that assertion – how can you claim to cause a headache in a mouse, when your study is trying to measure pain response in the first place?

I would guess that the injections are actually more similar in discomfort level to a human receiving a vaccination. As most people probably have observed, some vaccinations are more painful than others, depending on the salinity and contents. (Side note – received a new vaccination of MMR a few months ago at the insistence of my employer… MMR = liquid pain)

After injecting the mice, the authors used some fancy imaging to record things like, ear position, whisker twitches and eye movement. The results of these images are compiled into a scale based on the pain intensity of the injected solution. So, theoretically, the “mouse grimace scale” could be used to determine how much pain a mouse is in.

It’s important to note that the authors are looking at mild pain stimuli, not moderate (eg. fight wound, superficial surgery, etc.) or high (eg. invasive surgery, broken limb, etc.) levels of pain.

Granted, I haven’t read the entire paper yet, but as someone who’s worked with animals, I’m a little skeptical about measuring mouse facial expressions as a response to mild pain stimuli. Ear twitches could be in response to sound, perhaps at a frequency the authors do not detect. Blinking could be a result dryness in the eyes after being whisked out of a cage and then dropped back in, perhaps too quickly.

It should be interesting to read the actual article. Can’t trust popular media any more than you can trust scientists! I’m heading out to the university in a bit, so perhaps I’ll be able to download a copy there.

[Photo by Dale Tidy]