What's the difference between you and a serial killer?

British scientists have investigated the way psychopaths' brain stand apart from other 'normal' people's brain and found less activity in brain areas involved in assessing the emotion of facial expressions.

In particular, psychopaths are far less responsive to faces that emote fear, partly explaining psychopathic behavior.

Criminal psychopaths are people with aggressive and anti-social personalities who lack emotional empathy but they have a normal appearance, being able to deceive very well people around them, unlike psychotic criminals, with their erratic behavior.

Psychopaths can commit hideous crimes, such as rape or murder, without showing signs of remorse or guilt.

Researchers believed that with psychopathic disturbed ones lack empathy because they have defects in processing facial and vocal expressions of distress, such as fear and sadness, in others.

The researchers scanned brain activity in 6 psychopaths and 9 normal people while presenting them pictures of faces showing different emotions.

Both groups had increased brain activity in response to happy faces compared with neutral faces, but this increase was slighter among the psychopaths.

By contrast, when processing fearful faces, the healthy volunteers increased brain activity while the psychopaths decreased brain activity.

Thus, while psychopaths can process happiness, the same does not happen in case of fear.

"These results suggest that the neural pathways for processing facial expressions of happiness are functionally intact in people with psychopathic disorder, although less responsive."

"In contrast, fear is processed in a very different way."

The incapacity to recognize and emotionally respond to facial and other signals of distress may unleash psychopaths' failure to block behavior that causes distress in others and their lack of emotional empathy.

"If people with psychopathy can't process the emotion of fear and that is mirrored in terms of their brain activity, as this study suggests, that will help us understand the cognitive deficits."

"But it is still a long way to finding out what to do about that. We are a long way from knowing how to treat psychopathy." said Dr Nicola Gray, from Cardiff University's School of Psychology.