A new study has revealed why people often fail to empathise with strangers' pain, if they belong to a different race than their own.
In an imaging study of Chinese and Caucasian people, it was found that the participants' brains respond less strongly to the pain of strangers whose ethnicity is different when compared with strangers of their own race.
"It's one of a string of papers that have come out in the cognitive neuroscience literature that helps us to understand some of the unfortunate ways in which racial group identity can influence our reactions to other people," New Scientist magazine quoted Martha Farah, a cognitive neuroscientist at the University of Pennsylvania in Philadelphia, as saying.
In earlier research, it was shown that the amygdala, a brain area implicated in fear, responds more strongly to pictures of people whose ethnicity is different from the viewer's, but the responses aren't uniform.
Other research has shown that activity in other brain areas can dampen the amygdala.
In order to determine how ethnicity also sways the brain's sense of empathy, Shihui Han and colleagues at Peking University in Beijing conducted their experiments on 17 Chinese and 16 Caucasians volunteers.
All the participants were shown videos of a person being poked in the cheek with a Q-tip cotton bud or a hypodermic syringe, while they had their brains scanned on a functional MRI machine.
The films sparked activity in a region called the anterior cingulate cortex (ACC), which also lights up when people are in pain themselves.
But, for Chinese volunteers, the sight of another Chinese person in pain prompted more of an increase in ACC activity than the pain of a Caucasian person.
Caucasian volunteers from the US, Europe, and Israel also reacted more strongly to sight of another white person in pain.
Farah cautioned that such automatic neural responses did not necessarily translate into behaviour.
"Just because there is this difference in ACC response it doesn't mean that we are inevitably going to behave less empathically toward the other group," she added.
As expected, when the volunteers were asked "how painful do you think the model feels?" or "how unpleasant do you feel when observing the video clip?" Chinese and Caucasians volunteers reported that they felt each other's pain about equally.
The study has been published in the Journal of Neuroscience.