The researchers studied the phenomenon known as “emotional contagion of pain,” a key component of empathy which has to do with our ability to experience the pain of strangers.
Previous research by the same team has shown that both mice and humans have this ability, particularly when the person in pain is somebody they know. That research also showed that stress levels rose in mice and humans when they were around strangers, inspiring the researchers to investigate a potential link between stress and empathy.
In the first part of the experiment, the researchers gave mice metyrapone, a stress hormone blocker, which caused the mice to react to strangers in pain the same as they responded to cagemates in pain — thereby suggesting a boost in empathy. Another test found that when the mice were put under stress, they showed less empathy towards their cagemates.