SCIENTISTS have discovered a circuit in our brain that lets us predict when someone is about to lie to us. Humans have the ability to imagine what others are thinking and learn from their social habits - giving them clues as to when something is amiss. The findings could also help explain why some people become paranoid. Scientists from Oxford University scanned volunteers' brains while they chose one to two boxes to win points. The participants were sent advice on which box to choose from a second player who was sometimes dishonest. When the volunteers suspected they were being lied to, activity levels in the dorsomedial prefrontal cortex (DPFC), an area near the front of the brain, rose dramatically. If a volunteer thought the player was telling the truth the brain activity remained low. If their suspicions were proved wrong, the brain activity changed, suggesting the volunteers needed to rethink their opinion of the second player. The activity was predicting how trustworthy the advice would be, then reacting to the results of that prediction. Failures of this system could explain why those with schizophrenia are often paranoid. Research team leader Matthew Rushworth, of Oxford University, said: 'We are trying to find a specific circuit of the brain that performs social learning. His work was presented at a Cell Press Lablinks conference in London earlier this month.DM Chris Frith, of University College London, who was no t involved in the research, said: 'People with schizophrenia show false prediction errors which leads them to think their predictions are wrong. This leads to distrust and paranoia.' Matthew Rushworth is mapping the circuit of the brain he has discovered using an MRI scan which tracks the movement of water through the brain. A so-called 'theory of mind' is what lets us gauge how other people might be reacting or feeling and then helps them make decisions based on that information. Scientists believe that people with some forms of autism, particularly Aspergers' Syndrome may be missing this inbuilt 'theory of mind'. DM