Jan 21, 2015 12:51 PM EST
Most people are able to feel empathy for a friend or loved one who is experiencing physical or emotional pain. But it is often far more difficult to experience this same feeling when it is a stranger. Researchers now believe, however, that one of the major factors that prevent us from empathizing with others is stress.
Perhaps surprisingly, the ability to share another's emotions -- or not -- is equally demonstrated by both mice and people, says Jeffrey Mogil, a neuroscientist at McGill University, whose team studied the link between stress and empathy in experiments on the laboratory animals and human volunteers.
"The really cool thing about this is that you get exactly the same findings in mice and people," Mogil says.
Past studies have shown that both mice and people can both experience empathy for someone else's pain, especially if that individual is familiar. Those same studies have also demonstrated that stress levels rise in both rodents and people when they are in the presence of someone they do not know.
To find a link between stress and empathy, researchers treated male mice with the drug metyrapone, which blocks the stress hormone cortisol, to see how they would respond to pain in other mice.
The treated mice then began reacting to the unfamiliar mice in a manner normally reserved for cagemates showing signs of increased pain behaviors. However, when the scientists stressed the mice, they showed less empathy when their fellow rodents showed signs of pain.
Researchers then tested the empathy in college students, as well, using the "cold pressor" test, in which one subject plunges one hand into ice water for 30 seconds, then rating the pain on a scale of no pain to the worst pain imaginable.
When tested alone, the students ranked the pain about midway on the scale. However, they reported greater discomfort when paired with a friend also taking the same test, and showed more pained facial expressions and often touching their own hands when watching someone else's suffering.
Mogil says that the results are somewhat counterintuitive -- one would expect that being tested across from a friend would reduce the level of pain.
"But it doesn't make it better, it makes it worse," Mogil says. "And the reason for that, we believe, is that your pain is being added onto by the empathy for your friend's pain. This extra bit of pain is actually coming from the contagion from the other person."
In contrast, when the volunteers were paired with strangers, their pain ratings were the same as when tested alone. However, when given the stress-blocking metyrapone, they reported increased pain from the ice water.
"So we think what is preventing people from empathizing with each other on this very basic level is the fact that they're stressed because they find themselves in close quarters with someone they've never met before. So their empathy is unable to present itself."
Tony Buchanan, a neuroscientist at St. Louis University who also studies the effects of stress, says the McGill findings suggest that finding ways to reduce stress could potentially increase interpersonal empathy.
"In Mogil's study, people showed this empathy response to their friends but not to other classmates, who are just like them presumably. They're just like them, but they don't know them," Buchanan says.
"The idea would be: how do we get that empathy between the dyads in this study to extend to people who are your neighbors, to people who live across a border from you, to people who are a different religion?"
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