The honest truth: fMRI beats polygraph in detecting lies

For some people, lying can be extremely difficult to do, while others let it slip right off the tip of their tongue. New data suggests truth can be found when using fMRI to scan people’s brains, to a degree of accuracy better than a traditional polygraph test.

Studies showed the ability for fMRI to detect someone lying with up to 90 percent accuracy, where as a polygraph ranges from chance to 100 percent, varying from different studies. In work published in the Journal of Clinical Psychiatry, researchers in the Perelman School of Medicine at the University of Pennsylvania found that when a lie is told, experts can see on fMRI scans that the area of the brain linked to decision making lights up.

The study’s lead author, Daniel D. Langleben, MD, and colleagues were the first to study these two modalities with participants in a blinded experiment. The data adds further clarity to this technology, lending scientific data when looking at fMRI data for criminal legal proceedings. 

Twenty-eight participants were given the Concealed Information Test, also known as the Guilty Knowledge Test, while hooked to a polygraph or lying inside an MRI scanner. Each of the participants took both tests in different order, hours apart and were instructed to answer “no” to questions about numbers, making one of the six answers a lie.

The results showed polygraph experts incorrectly identified the lie. When reversing the scenario, neither the fMRI or polygraph experts were perfect; however, data suggests fMRI experts were 24 percent more likely to identify the lie.

Although the study was not designed to test both modalities in sequence, researchers made another observation when comparing accuracy of both devices. Both fMRI and polygraph were 100 percent correct in 17 of 28 cases when agreeing on what the concealed number was.

Researchers are not certain that fMRI will take precedence in court rulings, but the ability to spot a lie is enough reason for further investigation.