Photo: Tetra Images/Corbis; Illustrated By Ly Ngo.
For decades, one of the main methods we've used to learn about the human body — from the brain to metabolism to cancer — is by studying mice. In many ways, they're the perfect test subjects: They're docile, they're inexpensive, and (due to extensive inbreeding) there's comparatively little genetic variance between them, making it possible to conduct a wide variety of experiments without having to worry about results being compromised by large differences in DNA. And, most importantly, their biological and behavioral systems closely resemble our own.
But, we may need to find a new source of scientific knowledge. Researchers at McGill University noticed, during the course of a different experiment, that the mice responded less intensely to pain when humans were present. They decided to do some formal tests to figure out just how people affect mice in a lab environment.
The results, which were published today in the journal Nature Methods, were pretty striking. The researchers injected mice with a pain-inducing chemical, and found that the presence of male researchers caused a 36% decrease in both male and female mouse subjects' outward signs of pain.
Were the mice actually experiencing less pain? Not quite. The researchers suspected the rodents were experiencing stress-induced analgesia, a protective mechanism generated by the body that reduces physical pain during times of elevated anxiety (like that caused by the presence of predators). In order to test if stress was a factor, the team placed T-shirts worn by men into the mice enclosures, this time without causing the mice any physical pain. The mice displayed numerous signs of anxiety, including elevated levels of the stress hormone corticosterone, increased defecation, raised body temperature, and thigmotaxis, or the tendency to hug the wall of the enclosure. Importantly, the presence of women (or their clothing) caused only a very slight stress effect on the mice.
Of course, when you think about the countless studies that based their results on the reactions of mouse subjects, it becomes clear that this finding could potentially be a very, very big deal. As study author Jeff Mogil told The Verge, this phenomenon "may have confounded, to whatever degree, some very large subset of existing research."
So, where does science go from here? Mogil suggests that it might be a bit premature to swear off mouse subjects altogether, especially considering that the stressful effects of male researchers' presence largely faded after 45 minutes. Also, the mice were less anxious when the men were accompanied by at least one woman — yet another good reason to expand female presence in the authorship of scientific studies.
On that note, we think it's pretty funny that no one ever thought to check to see if mice were afraid of men. In a field that's currently dominated by men, that seems like a pretty good question.