Researchers at Duke University and Princeton University suggested that this function may disengage when people encounter others they consider disgusting, thus "dehumanising" their victims by failing to acknowledge they have thoughts and feelings.
This shortcoming could shed light how a father in Louisiana bludgeoned and beheaded his disabled 7-year-old son last August because he no longer wanted to care for the boy.
It may also help explain how propaganda depicting Tutsi in Rwanda as cockroaches and Hitler's classification of Jews in Nazi Germany as vermin contributed to torture and genocide, the study said.
"When we encounter a person, we usually infer something about their minds. Sometimes, we fail to do this, opening up the possibility that we do not perceive the person as fully human," said lead author Lasana Harris, an assistant professor in Duke University's Department of Psychology and Neuroscience and Centre for Cognitive Neuroscience.
Social neuroscience has shown through MRI studies that people normally activate a network in the brain related to social cognition - thoughts, feelings, empathy, for example - when viewing pictures of others or thinking about their thoughts.
But when participants in this study were asked to consider images of people they considered drug addicts, homeless people, and others they deemed low on the social ladder, parts of this network failed to engage.
The result is what the researchers call "dehumanised perception," or failing to consider someone else's mind.
Such a lack of empathy toward others can also help explain why some members of society are sometimes dehumanised, they said.
The study appears in a recent issue of the Journal of Psychology.