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MRI Lie Detection To Get First Day In Court

Publication Date: 
March 16, 2009
Alexis Madrigal
Wired News

Professor Henry T. "Hank" Greely and Emily R. Murphy, Fellow at the Center for Law and Biosciences, are quoted in a Wired News story about a request by defense attorneys in a sexual abuse case to admit as evidence an fMRI scan, which shows brain activity based on oxygen levels, to prove a client's innocence. WiredNews writes:

In an upcoming juvenile-sex-abuse case in San Diego, the defense is hoping to get an MRI scan, which shows activity levels based on oxygen levels in the brain, admitted to prove the abuse didn't happen.

The technology is used widely in brain research, but hasn't been fully tested as a lie-detection method. To be admitted into court, any technique has to be "generally accepted" within the scientific community.


"The studies so far have been very interesting. I think they deserve further research. But the technology is very new, with very little research support, and no studies done in realistic situations," Hank Greely, the head of the Center for Law and the Biosciences at Stanford, wrote in an e-mail to

Lie detection has tantalized lawyers since before the polygraph was invented in 1921, but the accuracy of the tests has always been in question. Greely noted that American courts and scientists have "85 years of experience with the polygraph" and a wealth of papers that have tried to describe its accuracy. Yet they aren't generally admissible in court, except in New Mexico.


According to Emily Murphy, a behavioral neuroscientist at the Stanford Center for Law and the Biosciences who first reported on the fMRI evidence, the case is a child protection hearing to determine if the minor should stay in the home of the custodial parent accused of sexual abuse.


"Having studied all the published papers on fMRI-based lie detection, I personally wouldn't put any weight on it in any individual case. We just don't know enough about its accuracy in realistic situations," Greely said.

Laboratory studies using fMRI, which measures blood-oxygen levels in the brain, have suggested that when someone lies, the brain sends more blood to the ventrolateral area of the prefrontal cortex. In a very small number of studies, researchers have identified lying in study subjects with accuracy ranging from 76 percent to over 90 percent (pdf). But some scientists and lawyers like Greely doubt that those results will prove replicable outside the lab setting, and others say it just isn't ready yet.


All these theoretical considerations will be put to the test for the first time in a San Diego courtroom soon. Stanford's Murphy reported that the admissibility of the evidence in this particular case could rest on which scientific experts are allowed to comment on the evidence.

"The defense plans to claim fMRI-based lie detection (or “truth verification”) is accurate and generally accepted within the relevant scientific community in part by narrowly defining the relevant community as only those who research and develop fMRI-based lie detection," she wrote.

Murphy says that the relevant scientific community should be much larger, including a broader swath of neuroscientists, statisticians, and memory experts.

If the broader scientific community is included in the fact-finding, Greely doesn't expect the evidence to be admitted.

"In a case where the issues were fully explored with good expert witnesses on both sides, it is very hard for me to believe that a judge would admit the results of fMRI-based lie detection today," Greely said.