The mere thought of being interrogated—by a parent, boss or significant other—is enough to make one's blood pressure rise and pulse and breathing rates race. But contrary to popular belief, these signs of anxiety are not reliable indicators of a person's honesty. Instead, researchers are looking into the brain to separate liars from truth tellers.

The act of lying or suppressing the truth triggers activities in the brain that send blood to the prefrontal cortex (located just above the eye sockets), which controls several psychological processes, including the one that takes place when a person crafts a new rather than a known response to something. "Lying is an example of this type of executive response, because it involves withholding a truthful response," says Sean Spence, a professor of general adult psychiatry at the University of Sheffield in England. "When you know the answer to a question, the answer is automatic; but to avoid telling me the true answer requires something more."

Spence and colleagues use functional Magnetic Resonance Imaging (fMRI) technology to determine whether someone is fibbing by tracing blood flow to certain areas of the brain, which indicates changes in neuronal activity at the synapses (gaps between the neurons). "If you're using fMRI, the scanner is detecting a change in the magnetic properties in the blood," he says. More specifically, hemoglobin molecules in red blood cells exhibit different magnetic properties depending on the amount of oxygen they contain. The most active brain regions use—and thereby contain—the most oxygen.

An fMRI is a full body scanner—"rather like being in a long cigar box," Spence says. The subject is completely immersed by the machine, which contains microphones, speakers and a keyboard that enable him or her to communicate with researchers. Researchers compare images taken of the subjects at rest with those snapped after they had been asked to respond to a series of questions.

Polygraph, or lie detector, tests are the most well-known method of discerning fact from fiction, but researchers say they are not reliable because they measure anxiety based on a subject's pulse or breathing rate, which can easily be misread. "They're not detecting deception but rather the anxiety of being…[accused of deception]," Spence says. "It's known that psychopaths have a reduced level of anxiety," that would allow them to fool a polygraph. The fMRI, he says, images the actual processes involved in deception.

Spence's research faced its greatest test in June during a demonstration of the technology on an episode of a three-part English reality TV show called Lie Lab, which studied the truthfulness of a man accused of being a terrorist, a woman who claimed to have been abused as a child, and a woman convicted of poisoning a child in her care. Spence and his team used an fMRI to study Susan Hamilton of Edinburgh, Scotland, who in 2003 was convicted of poisoning with salt a girl diagnosed with a terminal metabolic condition. Hamilton, who was in charge of feeding the child via a feeding tube that led directly into her stomach, was arrested after the girl was admitted to the hospital with massive blood sodium levels. The police testified that a syringe full of salt was found in Hamilton's kitchen, but she denies any knowledge of it. The woman was released from prison last year and has continued to search for ways to publicly prove her professed innocence.

2 Comments

1. 1. Ira Kaur 09:33 PM 11/16/07

   What about rehersed answers? For instance if I stole something, yet I have rehersed in my mind a specific senario that I will use as a response if someone enquires about it. Would this possibily cause a false reading from this particular test?

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2. 2. larrygreenemeier 11:16 PM 11/16/07

   Hi Ira,
   
   Based on my research, you would have to have rehearsed that answer thoroughly to be able to bypass your brain's normal processes. I'm not saying it's impossible, but you would have to be able to answer without hesitation. I suppose the vendors and researchers trying to make this work will run into this sooner or later.
   
   Larry

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