Radio Lab delves into the mystery:
Yang and her colleagues put all 49 people, both the liars and the non-liars, into a magnetic resonant imaging scanner and took pictures of their prefrontal cortex. They chose to focus on this area of the brain because previous studies had shown that the prefrontal cortex plays a role in both lying and in antisocial behaviors.
If you could look into this part of the brain, which sits right behind your forehead, you would see two kinds of matter: gray and white. Gray matter is the groups of brain cells that process information. Most neuroscience studies focus on gray matter. But nearly half the brain is composed of connective tissues that carry electrical signals from one group of neurons to another. This is white matter. Roughly, gray matter is where the processing happens, and white matter connects different parts of the brain, helping us to bring different ideas together.
The liars in Yang’s study had on average 22 percent to 26 percent more white matter in their prefrontal cortex than both the normal and antisocial controls. Yang speculates that the increase in white matter means that people who lie repeatedly and compulsively are better at making connections between thoughts that aren’t connected in reality — like, say, “me” and “fighter pilot.”
Interesting stuff. As a culture, we draw this big distinction between lies we tell to other people and lies we tell to ourselves (aka self-delusions). The brain, however, is the ultimate category buster. I wonder if it also distinguishes between these different kinds of dishonesty. For instance, the prefrontal cortex is also responsible whenever the brain deceives itself. People who benefit from the placebo effect, or think expensive wine tastes better than cheap wine (even when it’s actually the same wine), or are convinced that discounted energy drinks are less effective, are also liars: the only difference is that their prefrontal cortex is deluding the rest of the brain, and not some other brain.
I’d like to see a study that compared self-deception and the deception of others. Would there be a big difference? I’d expect there to be some extra cingulate activity when we lie to others, since the cingulate seems to be responsible for monitoring our social reputation. But the source of the lie itself – the promethean prefrontal cortex – just might stay the same.