Jeffrey Mogil’s students suspected there was something fishy going on with their experiments. They were injecting an irritant into the feet of mice to test their pain response, but the rodents didn’t seem to feel anything. “We thought there was something wrong with the injection,” says Mogil, a neuroscientist at McGill University in Montreal, Canada. The real culprit was far more surprising: The mice that didn’t feel pain had been handled by male students. Mogil’s group discovered that this gender distinction alone was enough to throw off their whole experiment—and likely influences the work of other researchers as well.
“This is very important work with wide-ranging implications,” says M. Catherine Bushnell, a neuroscientist and the scientific director of the Division of Intramural Research at the National Center for Complementary and Alternative Medicine (NCCAM) in Bethesda, Maryland, who was not involved in the study. “Many people doing research have never thought of this.”
Mogil has studied pain for 25 years. He’s long suspected that lab animals respond differently to the sensation when researchers are present. In 2007, his lab observed that mice spend less time licking a painful injection—a sign that they’re hurting—when a person is nearby, even if that “person” is a cardboard cutout of Paris Hilton. Other scientists began to wonder if their own data were biased by the same effect. “There were whisperings at meetings that this was confounding research results,” Mogil says.
So he decided to take a closer look. In the new study, Mogil told the researchers in his lab to inject an inflammatory agent into the foot of a rat or mouse and then take a seat nearby and read a book. A video camera trained on the rodent’s face assessed the animal’s pain level, based on a 0- to 2-point “grimace scale” developed by the team. The results were mixed. Sometimes the animals showed pain when an experimenter was present, and sometimes they seemed just fine. So, on a hunch, Mogil and colleagues recrunched the data, this time controlling for whether a male or a female experimenter was present. “We were stunned by the results,” he says. The rodents showed significantly fewer signs of pain (an average of a 36% lower score on the grimace scale) when a male researcher was in the room than when a female researcher—or no researcher at all—was there.
Read more at: http://news.sciencemag.org/brain-behavior/2014/04/male-scent-may-compromise-biomedical-research