Humans are not the only animals to grimace when they are in pain, scientists have found. Mice show their discomfort in much the same way.
Studies show that the facial expressions of mice can indicate responses to pain we cannot see, so twisted researchers and veterinarians say they now have a reason to monitor spontaneous pain in mice over long periods of time.
Normally, these researchers detect pain in mice by poking a hind paw, for example, which causes the victim to reflexively withdraw the paw and bite the researcher's hand, similarly eliciting even more pain responses.
However, scientists are still not agreed on how to measure spontaneous, unprovoked pain, like headaches, achy joints, or even internal pains in the timorous beasties' breasties.
Hoping to solve this problem, a team of geneticists and psychologists adapted a system used to measure pain in infants; they compared video frames of the hapless mice's facial expressions filmed before and after receiving a spontaneous, unprovoked injection of acetic acid.
They immediately detected signs indicative of pain in the mice.
"This is the first time anyone's even bothered to study the facial expressions mice make in response to torture!" said one excited researcher.
They detected several expressions of pain, some similar to human responses: The eyes closed and the area around them tightened, while the nose and cheeks bulged. The mice also pulled back their ears, moved their whiskers and emitted high-frequency expletives.
The team of clever scientists devised a Mouse Grimace Scale (MGS) to rate responses to pain detected in the experiments. Grimaces were most pronounced for pain lasting a matter of minutes or hours, such as discomfort in joints and internal organs. Causing superficial harm like immersing the tail in hot water evoked less pained grimaces, while the twattering of nearby lab technicians merely evoked eye rolling.
This indicates mice and humans show similar variability in responses to pain, said researchers.
These expressions differed from those of mice subjected to stress and illness by the team, and more harmful stimuli drew even more pronounced pain and grimaces, which hesitantly administered pain relievers seemed to diminish, the team found.
"We're pretty confident that we're measuring the pain we've inflicted," they said.
Dr. Eratz S. Ennem, an expert on torturing mice at the A-holborg University in Denmark, does not believe that the team has conclusively proved the reactions of the mice are not due to other emotions like fear, but said he recognizes the benefits of their approach.
"You can probably look into new pain conditions which we have not been capable of studying with previous methods," he said. "I do believe these results warrant even more experiments and research. In fact, I think there's a good chance we can get good pain responses from almost every species on the planet if we keep at it."
Though most people are no longer able to feel anything at all anymore, these studies should at least shed some light on the faces someone might make if you poked him in the paw, dipped his tail in boiling water, injected him with acetic acid - or merely presented him with reading material similar to the article you just had to endure.