Lying is natural. It’s actually pretty necessary for our survival. Can you imagine always having to tell the truth? “How old do you think I am?” or “Do you like my cooking?” are questions we don’t always want to answer honestly, and so we don’t. While additional inquires are often suspended after our initial slightly falsified response, when further pressed, we may find ourselves a little slow to answer. That’s because lying actually takes a lot of work.

What is lying? The dictionary defines it as not telling the truth. It’s also a bit different from cheating or omitting a piece of information. It’s really about going slightly further and saying something other than the truth, such as “I think you’re eternally young!” or “So original, I would’ve never thought of doing that with anchovies!” It’s actually a dual effort: suppressing the truth and substituting it with something else.

Chances are you’ve seen movies where a superhandsome — usually benevolent — outlaw is captured by some kind of interrogation force and given a polygraph test. Of course, he is probably not asked to provide an opinion on someone’s age or cooking, but he is grilled to give up a crucial piece of information essential for the storyline. The truth of the matter is that polygraph tests are not really all that accurate.

The tests actually measure the stress we experience when lying by reflecting accelerated heart rate, rapid breathing, rising blood pressure, increased sweating, and other symptoms related to anxiety. That’s a problem. Consider the fact that sociopaths — who don’t have the capacity for empathy, guilt, and remorse — and those who learn to inhibit their stress responses can pass a polygraph test with flying colors. That’s because it misses the crucial component of lying, the neurological evidence of the decision to do it. So, then, where does that leave us?

Dr. Daniel Langleben, a psychiatrist at the University of Pennsylvania, asked himself the same question awhile back. He searched the web for answers and, of course, found nothing. He soon realized that fMRIs (functional magnetic resonance imaging) could reveal what has so far remained a mystery. In the journal NeuroImage, he concluded that “a neurophysiological difference between deception and truth” could be detected.

Since then, the science behind fMRI lie detection has quickly and significantly expanded. Because fMRIs enable researchers to map the brain’s networks as they engage in the process of deception, they can be considered fairly accurate lie-detection devices. Wired’s Steve Silberman wrote about his experience in Columbia University’s fMRI Research Center. Joining forces with Joy Hirsch, the head neuroscientist and founder of the facility, Silberman traced the process of how brain mapping actually works by completing several different tasks while inside the scanner.

“The first phase of [the] procedure is a baseline interval that maps the activity of my brain at rest. Then the ‘truth’ phase begins. Prompted by a signal in the mirror, I launch into an internal monologue about the intimate details of my personal life … I focus … on forming the words clearly and calmly in my mind, as if to a telepathic inquisitor … Then, after another signal, I start to lie … I plunge deeper and deeper into confabulation, recalling incidents that never happened while trying to make the events seem utterly plausible.”

There was a clear difference in brain function when Silberman lied and told the truth. Because he internally spoke his dialogue, the area of the cortex devoted to language lit up. Yet there was one stark difference: Scans showed increased activity when he was lying. When he was telling the truth, parts of the brain associated with emotion, conflict, and cognitive control — that is the amygdala, anterior cingulate cortex (ACC), caudate, and thalamus — were inactive, but when he wasn’t, they were on fire.

While the elevated activity in the ACC and its precise function are still somewhat unclear, Silberman noted that the caudate serves a similar function as an editor by assisting the brain in the balancing act of truth telling and fabricating lies. Key staples of fMRI deception mapping occur in the prefrontal cortex, just behind the forehead. Because most paradigms used in studying deception involve an experimenter telling the subjects to try to be deceptive in some way, they are not a real reflection of why some people engage in the behavior. Yet much insight into the neuroscience of lying has been accessed this way.

This article is updated from its initial publication in Brain World Magazine’s Winter 2014 issue.

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