Pathological lying may stem from an unusual imbalance of brain matter, say scientists at the University of Southern California. Working with senior investigators, doctoral student Yaling Yang scanned the brains of 12 self-described pathological liars as well as other volunteers who had no history of deception. Yang was surprised to find that the liars’ brains had 22 percent more white matter in the prefrontal regions that govern decision making and judgment. So-called white matter makes up the wiring among neurons, which are sometimes collectively called gray matter.

Pathological lying can be very complicated. People who do so must present information that appears correct and yet harbors falsehoods. “It may just be easier for them to tell lies,” Yang says, because the excessive white matter creates an abundance of connections among otherwise contradictory, compartmentalized data. Further studies are needed to determine if the fabricators are born with more white matter or develop it as a result of their frequent fibbing.

Other scientists who have done functional MRI scans of people lying in real time also point to excessive activation in the prefrontal lobes and say the patterns of activity can serve as reliable detectors of deception. If so, scanners could one day move from the lab bench to the court bench.