Can A Brain Scan Tell If You’re Lying?


Publish Date:
December 3, 2017
  • Keeffe, Patrick
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Searching for the truth is the very definition of what happens in criminal court.

Forensic science has long assisted in that quest.

However, other scientific tools — polygraphs, brain scans, and functional magnetic resonance imaging (fMRI) — remain largely inadmissible as evidence of guilt or innocence.

Henry T. Greely, JD, a professor of law at Stanford University in California and director of the Stanford Center for Law and the Biosciences, said any single study “needs to be viewed skeptically, no matter how good the investigator.”

“If five different teams replicated the Langleben study, I would feel much better about it, in part because it would have involved more than only 28 people,” he told Healthline. “Even then, lies told by people who know they are research subjects, and are following instructions to lie, may look very different from lies in real life.”

“That’s a very hard problem to solve,” Greely added. “We can’t go around arresting people to make them take an fMRI test to test ‘real’ lying. In any event, ‘significantly better’ than the polygraph is not very good. In almost every U.S. court, it is not good enough to be admitted, and most experts think it should not be used as often as it is outside of court. That’s the most important bottom line: better than the polygraph, even if true, isn’t good enough to be used for important decisions.”

Greely said judges in all the cases where the evidence has been presented have rejected fMRI after hearing expert witnesses because its results aren’t proven to be sufficiently accurate and the tests did not follow any well-established protocols.

Greely notes that DNA evidence for identification is a “much more scientifically easy process.”

“But it took two reports by the National Academy of Sciences and an FBI program to create protocols for its use,” he said, “and to accredit crime labs to do that testing before it was widely accepted. If fMRI-based lie detection is ever very useable — and I put the odds at about 50/50 in the next 10 to 20 years — similar things will have to happen.”

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