Does fMRI Lie Detection Have a Future in the Courtroom?


Functional Magnetic Resonance Imaging (fMRI) is a brain imagining technique developed in the 1990’s based on blood oxygenation levels in the brain. The underlying property upon which fMRI relies is hemoglobin’s tendency to exhibit different magnetic properties when oxygenated than when deoxygenated. By inducing a strong magnetic field on the subject and observing how the hemoglobin responds to the field, neurologists can determine which parts of the brain are experiencing greater blood flow during certain exercises. fMRI enables neurologists to link areas of the brain with certain activities or emotions; accordingly, development of fMRI has led to a greater understanding of psychological disorders. However, fMRI also faces much criticism regarding its underlying techniques and the ethics of admitting evidence that fMRI generates. We focus here on courts’ scientific arguments in rejecting fMRI lie detection evidence.

Rocky History with the Courts

Despite repeated attempts to introduce fMRI lie detection results into the courtroom, courts across the nation have widely rejected the proposition. In the 1993 case Daubert v. Merrell Dow Pharmaceuticals, Inc., the Supreme Court held that judges should act as gatekeepers with the discretion to exclude scientific evidence determined to be invalid; this came to be known as the Daubert test and still holds today for all scientific evidence submitted to the courts. fMRI-based lie detection services have been available to the public since 2006, but the question of the validity of the technique was formally brought in front the United States District Court for the Western District of Tennessee in U.S. v. Semrau in 2010. Of the two companies that offered the service, one stopped performing fMRI lie detection after the Semrau court ruled that the technology could not be validated because there were no known error rates for fMRI lie detection in real-world settings. The finding was affirmed in 2012, when the 6th Circuit heard the case on appeal and found that fMRI evidence does not pass the Daubert test.

Recent Developments

Although fMRI lie detection technology is still developing, there are still very few answers to the questions asked by the district court in 2010. Trials have yet to produce known error rates in real-world settings, and the field has not yet developed a standardized methodology for fMRI lie detection tests. Nonetheless, researchers are pushing forward, slowly seeking answers and solutions. Though there is not yet a consensus on which parts of the brain is active when lying, there is considerable agreement that the brain is more active overall when a person is lying. And just last year, a new study finally ran fMRI scans and polygraph tests in near-identical situations and found that fMRI scans are more reliable than polygraph tests in detecting lies.


The progress of science seems to headed in the direction of more standardized methods and more concrete evidence of the consistency of fMRI lie detection results. Nonetheless, the rest of the scientific community is rightly still doubtful of the possibility of fMRI lie detection being admitted as evidence. Even though fMRI results are now more reliable than those of polygraph tests – which only sit at 70% accuracy – the results of the fMRI technique are still not consistent enough to meet the threshold for admission into the courtroom. If there is hope for the future of fMRI evidence in courtrooms, it will likely be in the sentencing phase rather than the convicting phase. In fact, in 2009, an expert was allowed to testify in a death penalty case to demonstrate that the defendant should be less culpable due to signs of psychopathy in an fMRI scan. For now, it might be more likely that fMRI lie detection will assume a role similar to that of the polygraph test: not admissible to court but frequently used by law enforcement in the course of criminal investigations as an information-gathering tactic.

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