Polygraph tests are notoriously unreliable, yet thousands of employers, attorneys, and law-enforcement officials use them routinely. Could an alternative system using functional magnetic resonance imaging (fMRI), a technology that indirectly measures brain activity, better detect deceit? The U.S. government is certainly interested--it's funding research in the area--and two companies have already sprung up to commercialize this use of fMRI. But a recent scientific symposium concluded that little evidence exists to suggest that fMRI can accurately detect lies under real-life circumstances. Scientists who attended the symposium worried that this new generation of lie detectors will follow the path of the polygraph--a widely used technology with little scientific support and broad potential to do harm.

"As we move forward, we don't want to make the same mistakes as with the polygraph," said Marcus Raichle, a neuroscientist at Washington University Medical School, in St. Louis, and a speaker on the panel, which was sponsored by the American Academy of Arts and Sciences, an independent policy research center in Cambridge, MA. He emphasized that, like the physiological changes monitored during polygraphs, the brain-activity patterns measured during fMRI are not specific to deception, making it challenging to identify a brain pattern that definitively identifies a lie.

"The great danger is that something like fMRI is adopted as a means of lie detection and becomes the standard before it has been scientifically evaluated for this purpose," says Raichle in an e-mail written after the symposium. "The federal government does [approximately] 40,000 polygraphs a year, and I have heard speculation that as much as 10 times that amount may be being used in the private sector. If these numbers are anything like the real circumstance, then to have fMRI take over such an agenda prematurely would be very bad indeed."

The potential to detect lies by peering into the brain has been widely covered by the media in the past year or two, conjuring images of mind-reading chambers adjacent to metal detectors at airport security checkpoints. One company, California-based No Lie MRI, already has its product on the market. It advertises to employers, lawyers, the government, and individuals, claiming a 90 percent accuracy rate in identifying deception. But neuroscientists at the symposium criticized commercialization as premature. "I think there is very little basis for using those machines for [lie] detection, at least for now," says Emilio Bizzi, an MIT neuroscientist and president of the American Academy of Arts and Sciences.

But the intense interest in developing an alternative to the polygraph means that the technology is likely here to stay. Unbiased studies are needed to determine if and when fMRI could reliably detect deceit, scientists on the panel said. "Put this in the backdrop of the tens or hundreds of thousands of polygraph sessions being conducted in government and in the corporate world," says John Gabrieli, a cognitive neuroscientist at MIT.