Identifying deception is something humans have attempted to do for centuries. Initial techniques, such as facial expression interpretation, were developed without technology. Later, simple technologies, such as the polygraph, were designed to detect physiological changes consistent with the autonomic arousal that often accompanies the act of lying. More recently, a powerful technique, functional magnetic resonance imaging (fMRI), has gained popularity as a potential lie detector and is sometimes used commercially for this purpose.

fMRI detects changes in blood flow, and because more active brain areas experience enhanced blood flow, fMRI can provide information about neural activity level. Because the technique has been used successfully in neuroscience research focused on mapping functionality, the idea arose that fMRI should be useful in identifying the function of lying. Consistent with this notion, studies have shown that differences in brain activation revealed through fMRI can facilitate the identification of falsehoods. Further, a recent meta-analysis found a high degree of consistency among studies as to the areas of the brain involved in lying. These areas, located largely in the prefrontal cortex, are important for executive functioning.

If we contemplate the cognitive process of lying, the involvement of executive functions is intuitive. Specifically, while voluntarily lying, one must keep track of two sets of circumstances: those consistent with the truth, and those consistent with the lie. This requirement would certainly increase cognitive load and the activation of relevant brain areas. However, individual brain differences can produce inconsistent activity patterns. For example, a recent study showed that when criminals with antisocial personality disorder lied, they lacked the pattern of prefrontal activity that has consistently been observed in healthy volunteers.

Even when considering lying only in those who lack psychiatric illness, detecting lies through fMRI is complicated by several factors. First, whereas lying may necessitate enhanced cognitive processing, such cognitive processing can occur independent of dishonesty. Further, if one intends to lie, the resulting cognitive load is not necessarily eased while that person tells the truth. Accordingly, studies have found that those being dishonest demonstrate more activity in areas of the brain associated with executive functioning both when telling the truth and when lying.

Another complicating factor is that not all lies are equivalent. Though someone committed to telling the truth may be burdened with a smaller cognitive load, liars may be able to make their lies less cognitively laborious so that the activity associated with their dishonesty resembles activity normally associated with honesty. For example, researchers have shown that the patterns of brain activity associated with well rehearsed lies diverge from those associated with spontaneous lies.

As with the commercial use of fMRI in strategic marketing, use of fMRI for lie detection remains controversial and has yet to be deemed admissible in a court of law. Though fMRI is an effective tool for elucidating brain function, much more research is required to determine if this technique will provide a reliable method for revealing dishonesty.

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