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science. medicine. health.

Liar, Liar, Brain on Fire


The science of deception

Janice Gee

Fall 2005


deception lie brain cortex    “I did not have sexual relations with that woman.” Whether inside the hallowed halls of the United States Congress, or in the office of a high school principal, lie detection reigns paramount in society. From administering sophisticated polygraph tests to simply examining whether or not a person can maintain eye contact, we are constantly searching for methods to determine whether or not a person is lying. Now, there might exist a way to scientifically prove this fact as researchers begin to pinpoint regions of the brain associated with deceitful behavior by using the latest in brain scanning technology.

    Much of this research has focused on a region of the brain known as the prefrontal cortex. According to Daniel Krawczyk, PhD, of the Helen Wills Neuroscience Institute at the University of California, Berkeley, the prefrontal cortex is central to functions such as problem solving, planning, reasoning, and analyzing known facts. These functions, which are often used in deception, are known as cognitive functions. According to Krawczyck, “the prefrontal cortex is thought of as ‘uncommitted cortex,’ because there is not one function that it is supposed to do. It is the executive center of the brain.”

    The prefrontal cortex is also the center for the discretion between moral and immoral decisions. “[It] plays a key role in deception for several reasons. This is an area which processes all kinds of information, emotional or neutral, tags them with reward values, and finally makes decisions based on the information. This is also an important region for rule-retrieving, rule-maintaining, and making moral-judgments. All these are important for deception,” reveals Yaling Yang, a PhD candidate at the University of Southern California.

    Yang believes that prefrontal white matter plays a crucial role in the act of lying. In a recent study, he used structural magnetic resonance imaging technology to examine and compare the brains of pathological liars, antisocial individuals, and normal individuals. He discovered that the brains of pathological liars contain a higher amount of white matter in the prefrontal cortex compared to those of normal individuals, suggesting that an increase in white matter may be related to one’s propensity for lying. “Based on developmental theories, a child starts showing the ability to lie at around age three. This ability quickly develops and peaks approximately at age ten. This is the period of time [during which] the white matter volume in the brain increases dramatically to almost 60 percent in a normal child,” he says. Yang also adds that research demonstrates that a decrease in prefrontal white matter results in a limited ability to lie; he uses autistic children, who cannot tell lies very successfully, to illustrates this finding. Yang indicates that “autistic children only show 10 percent white matter increase between the ages of three to ten. Failure in the development of white matter [may have resulted] in their [lying] impairment.”
 
    In addition revealing details about the structure of the brain, brain scanning technology can also detect increases in neuronal activity within specific regions of the brain when a person is lying. Daniel Langleben, PhD, of the University of Pennsylvania, used functional magnetic resonance imaging scans (fMRI) to determine changes in brain activity during the act of lying. According to Dr. Krawczyk, fMRI scans measure the oxygen flow in the regions of the brain that are being examined. He asserts that “fMRI scans are a way of getting very precise information on what parts of the brain are involved in certain functions.”

    In his study, Dr. Langleben discovered an increase in neuronal activity in the both the prefrontal cortex and another cortical region, the anterior cingulate cortex, while an individual was lying. The anterior cingulate cortex, located roughly in the center of the brain, regulates cognitive functions such as reward anticipation and decision-making. According to Dr. Langleben, increased activity in the anterior cingulate cortex and the prefrontal cortex suggests that the brain must work harder to lie. Based on this data, he concluded that the brain naturally wants to express the truth. In his view, lying requires the brain to suppress the truth, think of a lie, and express the lie. He reasons that this “extra work” translates to an increase in brain activity.

    Because of the ability of fMRI scans to produce precise readings of brain activity, many have proposed these scans could possibly replace polygraph tests as the most commonly used lie detecting method. However, Dr. Langleben reminds us that “[an fMRI scan] is not a lie detector. It is simply a more accurate way to measure brain activity than any currently available noninvasive method.” Yang agrees, adding that “with more studies on this particular topic, brain imaging will have practical implications in lie detection. But I believe that using one technique is never reliable enough to draw any conclusion on whether an individual is telling a lie or not.”

    Dr. Krawcyzk also believes that fMRI scans cannot be used as lie detectors just yet. He stresses that lying is such a complex function that it is almost impossible to attribute the act of lying to any specific cortical areas. Therefore, it is difficult to automatically associate the increased activity in a specific region of the brain with lying. “We don’t do things with only one part; there are a variety of functions that are performed by the same area,” he states. “It’s just not possible to assign a specific function to every brain area, and therefore anything complicated can start to raise questions on whether it is truly responsible for the behavior.”

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