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Functional Magnetic Resonance Imaging to Detect Deception: Not Ready for the Courtroom

23 Pages Posted: 15 Apr 2011  

William A. Woodruff

Campbell University School of Law

Date Written: September 17, 2010


Despite media hype and at least two companies marketing themselves as offering scientific expert testimony admissible in US courts on whether a witness is telling the truth, recent decisions by a trial court in New York and a Federal Magistrate Judge in Tennessee indicate that replacing the jury deliberation room with a magnetic resonance imaging machine is not in the foreseeable future.

Functional magnetic resonance imaging (fMRI), an emerging field of neuroscience that seeks to correlate brain activity to behavior, has been touted by some to be the new lie detector. The MRI machine is able to “see” the increase in oxygenated blood as it fuels various regions of the brain during actions and activities. The hypothesis underlying fMRI as a lie detector is that telling the truth is the natural or normal response of the brain and one would not expect to see increased activity over and above the normal background level of brain activity. But when the subject begins to prevaricate, more brain activity is needed and more oxygenated blood is directed to those regions of the brain processing the “lie.” This blood oxygenation level-dependent (BOLD) differential is measurable by the fMRI.

Comparing the BOLD differential between subjects known to be telling the truth and then deliberately lying allows researchers to hypothesize that increased BOLD above the base line in certain regions of the brain when the subject is answering questions is an indication of deception.

It might be in the lab, but the rules of evidence as applied in US courts considers the citizens of the community selected to sit on the jury more reliable “lie detectors” than the new technology represented by fMRI. Two recent decisions, one in a Federal court applying the Federal Daubert standard and one is New York state court applying the Frye general acceptance test, rejected expert testimony based on the results of fMRI scanning.

In finding fMRI failed to satisfy the exacting standard of Federal Rule of Evidence 702, a Federal magistrate judge in United States v. Semrau measured the new technology against the Daubert reliability factors. fMRI passed the first two factors, testing and peer review. The court noted that the technology was certainly capable of and was being tested and that numerous articles concerning fMRI had appeared in the peer reviewed scientific literature.

The next two Daubert factors, the known or potential error rate and the existence and maintenance of standards, however posed significant problems. While there may be some identifiable error rates associated with fMRI in the controlled lab setting, it was undisputed that error rates in the “real world” application are completely unknown. Similarly, protocols exist for lab studies of fMRI but not such standards exist for real-life applications. In fact, Dr. Steven Larkin, the expert witness for plaintiff in Semrau, and one of the leading proponents of fMRI as a lie detector admitted to deviating from his own protocol in administering the test on Dr. Semrau.

Finally, the court found that fMRI as a reliable lie detector had not achieved general acceptance by the scientific community, the fifth Daubert factor. By failing to meet three of the five Daubert factors, the magistrate judge concluded that fMRI was not sufficiently reliable to admit under FRE 702.

The magistrate judge also found the use of fMRI to bolster Dr. Semrau’s credibility more prejudicial than probative. Relying primarily on cases excluding polygraph examinations taken without the knowledge or participation of the opposing party, the magistrate judge concluded that the unilateral fMRI test here lacked probative value because Dr. Semrau faced no negative consequences by undergoing the test. Accordingly, the evidence was excluded under FRE 403.

The New York case, Wilson v. Corestaff Services L.P., applied the Frye general acceptance standard to fMRI based expert testimony to bolster the plaintiff’s witness in an employment discrimination case. The court was troubled be the notion that fMRI based expert testimony would usurp the jury’s responsibility to determine the credibility of the witnesses, a dramatic departure from the traditions of a common law trial. Additionally, the court found the plaintiff was unable to show the use of fMRI to determine truthfulness had been generally accepted by the relevant scientific community, the standard for admissibility under Frye.

The analysis in Semrau and Wilson combined imposes significant hurdles to the admissibility of fMRI on the issue of witness credibility. The procedure failed to meet the reliability standards of FRE 702 and the general acceptance requirement of Frye. Furthermore, concerns over jury confusion, usurpation of the traditional function of the jury in judging credibility, and whether such testimony is even an appropriate matter for expert opinion raise additional hurdles. For proponents of fMRI expert testimony on witness credibility the obstacles to admissibility are significant under current law.

Keywords: fMRI, Brain Imaging, Lie Detection, Federal Rules of Evidence, Daubert, Frye, Expert Testimony

Suggested Citation

Woodruff, William A., Functional Magnetic Resonance Imaging to Detect Deception: Not Ready for the Courtroom (September 17, 2010). Available at SSRN: or

William A. Woodruff (Contact Author)

Campbell University School of Law ( email )

United States

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