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Psychopaths may give themselves away by how quickly and easily they can lie.

Scientists say they show less activity in the brain when processing emotions, suggesting they find it easier to suppress the truth and be deceitful.

Psychopathy is often associated with criminals but many people in the general population show psychopathic tendencies. Scientists at Hong Kong University tested 52 students who classified as having either high or low levels of psychopathy, which is a personality disorder characterised by a lack of empathy or feelings of guilt.

They were shown photographs of familiar and unfamiliar faces and asked whether they knew the person in the picture. When asked to lie, both sets of people took longer to respond. But after they were given instructions from researchers on how to respond, the psychopathic volunteers became much quicker at lying.

The participants underwent brain scans during testing and those with psychopathic tendencies, after being taught how to lie, were less detectable. Lying requires a lot of work in the brain, in repressing the truth, while manipulating working memory to come up with a lie.

The study suggests psychopaths, who are better at cognitive processing but worse at emotional processing, do not have to work so hard to resolve a moral conflict.

© Daily Mail