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Functional magnetic resonance imaging ? or fMRI - enables researchers to create maps of the brain in action as it process thoughts, sensations, memories, and motor commands. Since its introduction to experimental medicine ten years ago, fMRI has been successfully used in the prognosis of diseases like Alzheimer's and schizophrenia, and the evaluation of drug treatments. fMRIs have also been used in conjunction with neurosurgery to localize damage. More recently, researchers have claimed that fMRIs have given insight into the cognitive operations behind such complex and subtle behavior such as deception.

Daniel Langleben, a psychiatrist at the University of Pennsylvania, was one of the first scientists to research the technology's applications in deception. His foray into the area was, however, inadvertent. "When I was studying adolescent boys with ADHD, I was intrigued by the observation that these children had difficulty lying. Children with ADHD have impulse control problems, they cannot inhibit their reactions. As a result, the truth that is sitting there in their brains, just bubbles out". From this starting point, Dr. Langleben began to study whether there was a biological difference between truth' and lie', using fMRI. So, how exactly does fMRI project an accurate' representation of a truth' and a lie'?

In an interview, James Loughead, professor of neuropsychology at Penn and one of Langleben's collaborators, elucidated how brain fMRI is performed by placing the head or the entire body in the bore of an MRI scanner, built around a powerful electrical magnet (whose magnetic field is around 105 times stronger than the Earth's). The polarized magnetic field causes the hydrogen nuclei in water in the body to resonate and emit radiofrequency signals that are eventually reconstructed into a three-dimensional image that reflects the relative concentrations of the hydrogen nuclei in the tissues.

"The key quantification that an fMRI gives us is the haemodynamic response- or the Blood Oxygen Dependent Level (BOLD)," Dr. Loughead explained. "When local oxygen demand rises in response to increased electrical activity and metabolism, the BOLD signal changes. The BOLD signal can therefore tell us in which areas of the brain neurons are most active in response to various experiences". As an example, Dr. Loughead points to the BOLD pattern for a finger-tapping task. This simple task can be localized to the primary motor cortex consistently on a single subject basis,there is little or no room for error in this detection.

"Lying is an involuntary action; it's not something you can suppress," Loughead explained. "You need to exercise a system that is in charge of regulating and controlling your behavior when you lie more than when you say the truth". Langleben and Loughead used the Guilty Knowledge Test (GKT) in which subjects were given envelopes with a playing card in it, and they were asked to lie about the identity of the card. Once in the scanner, the subjects were shown a series of pictures of playing cards, including the one they had in their pocket, and they pressed yes' or no' to each card. When it came to the card they were hiding, they would say no'- and this would constitute a lie.

"The basis of the test is a robust human response to salience", says David Seelig, a graduate student in Langleben's lab. "If you were to present suspects with various murder weapons, including the one found at the crime scene, the reaction to salience is something that can be detected by the fMRI, and researchers can see which suspects show an increased brain response to the real weapon".

One safety precaution is that no metal objects can be worn or brought near the fMRI machine during operating hours; there have been disasters where the insuperable magnetic field of the scanner has essentially ripped out a patient's metal replacement, such as a pacemaker or any metal prosthetics.

According to the studies conducted by Langleben and Loughead, the parts of the brain that are most active during deception are the inferior frontal gyrus and the inferior parietal lobe (together they make up the prefrontal parietal network important in detecting salience) and bilateral frontal cortex. The increased blood flow to these areas, as represented by the BOLD patterns, indicated that these areas were working harder in telling a lie' than they were in telling the truth'. Langleben and Loughead have provided the desired cognitive markers that neuroscientists, psychologists, lawmakers and the general public have been looking for ever since the downfall of the polygraph. Their data also, however, raises some important questions- is deception in such an instructive manner (that is, the subject is essentially instructed to lie) really deception? As Seelig explains, the fMRI does not measure two important components of lying- the emotional response and the intention of the liar' to instill false belief in another person. "Telling a story is very different from simply responding to Yes' or No' questions; you have to maintain two realities. This requires the emotional component of deception, controlled by the limbic network." The limbic network includes the purported emotional center of the brain- the amygdala. These aspects, in addition to the cognitive component, give a more accurate representation of deception. Considering this, what are the implications of using an fMRI in legal and security milieu? If it is not a true representation, there is the risk of falsely incriminating someone, either in a situation as dire as court or as routine as job screenings.

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