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Patrick Guilfoile: How men mess things up

In science, one of the keys to successful experiments is to be able to control a single variable.

For example, a common method of studying pain is to inject an irritating compound into the lower leg of a mouse. (While this type of experiment may seem unpleasant, it is one of the few ways we have to test out new ways for treating pain in humans and other creatures.)

Their response (time spent licking their feet, or the intensity of grimacing) is compared to mice that have had harmless saline injected into their leg.

The single variable is (apparently) the type of compound injected in the leg.

Yet in spite of efforts to control experimental variables, researchers sometimes noticed anomalies in the pain responses.

Sometimes, mice seemed not be feeling much pain, even when they had been injected with an irritant.

Researchers at McGill University in Montreal, Canada noticed these puzzling results, and initially verified that the injection fluid had been correctly mixed.

Once that was established, they next decided to explore whether the presence or absence of a scientist in the room was an unanticipated variable in these experiments.

In their initial experiment, researchers injected an irritant into the lower leg of mice, and measured their pain response.

Whether or not a scientist was present in the room after the injection was the variable.

The puzzling result was that sometimes the presence of a person in the room made a difference, and sometimes it didn’t.

After some additional analysis, the researchers found something startling.

If no one was in the room, or if a woman was in the room, the mouse manifested a similar pain response.

However, if a man was in the room, the mice demonstrated significantly less evidence of pain.

Further experiments showed that the response to males was at least partially driven by smell.

Simply putting an odiferous T-shirt from a man in the room was enough for the mice to show a reduced pain response.

Yet it wasn’t just a matter of mice pretending not to feel pain.

The presence of a male, or male scent, induced a stress response, which actually led the mice to feel less pain. (The level of stress was determined based on the amount of stress-induced chemicals in the blood, and on an increase in rectal temperature in the mice.)

This research provided a clear illustration of the importance of properly controlling variables in scientific experiments — otherwise, scientists may mistakenly associate a particular cause (for example, the use of pain medication) with an effect (a reduction in pain), when in reality, the presence of a man in the room was actually the cause of the pain reduction.

This research also suggests that, instead of reaching for a bottle of aspirin for aches and pains, you might want to simply sniff the underarms of some guy’s smelly T-shirt.

More information is available in:  Nature Methods (2014) doi:10.1038/nmeth.2935   Olfactory exposure to males, including men, causes stress and related analgesia in rodents. Robert Sorge and others

PATRICK GUILFOILE has a doctorate in bacteriology and is the associate vice president at Bemidji State University.