Truth Serum

Lying generates unique brain activity that can be measured by functional magnetic resonance imaging (fMRIs), brain scans that could someday morph into a forensic tool far more potent than the flawed polygraph test.

Researchers gave 18 subjects a playing card, then offered them money to lie to a computer about the card while undergoing an fMRI. When subjects lied, the scans revealed increased activity in several regions of the brain, including the anterior cingulate gyrus, which is implicated in conflict monitoring, attention and response inhibition. Head researcher Daniel Langleben, M.D., a professor of psychiatry at the University of Pennsylvania, says this confirms that the brain's "default" response is to tell the truth. "No area of the brain works harder to tell the truth than to lie" says Langleben.

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Forensic experts are hopeful because fMRIs measure complex mental processes, while polygraph tests pick up skin and blood pressure changes that can be misleading. Langleben says the next step to ready brain scans for forensic use is to monitor spontaneous acts of deception. Langleben modeled his study on classical deception research, in which subjects are instructed to lie. The study was presented at the Society for Neuroscience annual meeting.

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