A NEURAL circuit has been identified that allows people to predict whether someone is going to lie to them. The finding could help to explain why some people become paranoid.

Humans have “theory of mind” – the ability to imagine what others are thinking and learn from their social habits. “We’re trying to find a specific circuit that performs social learning,” says Matthew Rushworth at the University of Oxford, who presented his work at a Cell Press LabLinks conference in London on 3 December.

Rushworth’s team scanned volunteers’ brains while they chose one of two boxes to win points. They 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 rose in the dorsomedial prefrontal cortex (DPFC), an area near the front of the brain. If the volunteer thought the player was telling the truth the activity remained low. If their suspicions were proved wrong, the activity changed “suggesting the volunteers needed to rethink their opinion of the second player”, says Rushworth. In effect, the activity was predicting how trustworthy the advice would be, then reacting to the results of that prediction (Nature, vol 456, p 245).

In effect, the brain activity predicted how trustworthy the incoming advice was going to be


Failures of this system could explain why those with schizophrenia are often paranoid, says Chris Frith of University College London, who was not involved in the study. “People with schizophrenia show false prediction errors: they keep thinking their predictions are wrong,” he says. This leads to distrust and paranoia.

Rushworth is now mapping the circuit using diffusion-weighted MRI, which tracks the movement of water through the brain, to find out which areas the DPFC is linked to. This might ultimately allow the design of targeted treatments for paranoia.