Should Brain Scan Lie Detection Be Used as Evidence in Court?

By Libby Rozbruch
Libby Rozbruch is a junior at the University of Pennsylvania studying Psychology.

Over the past decade, scientists have been exploring the potential of functional magnetic resonance imaging (fMRI) as a method for lie detection. fMRI measures small, variable changes in the ratio of oxygenated blood to deoxygenated blood during a particular task or when a particular stimulus is presented. When a specific area of the brain is active, there is a local increase in oxygen-rich blood. In turn, fMRI allows scientists to assess and identify increased activity in brain regions associated with the cognitive processes required for lying. [1] The question is – should information acquired from this type of brain imaging technology be used as evidence in the courtroom?

While the incursion of neuroscience into the legal sphere imposes various negative implications, it could also revolutionize the entire legal system. The traditional lie detection method, the polygraph, measures an individual’s physiological reactions to direct questions. fMRI, however, measures brain activity at the source that gives rise to the skin response, heart rate, blood pressure, and respiration changes registered by the polygraph. [2] fMRI-based lie detection utilizes an objective and more reliable method for truth verification, as its results do not require subjective interpretation.
​
Additionally, fMRI is less susceptible to confounding influences such as anxiety or stress, as these mental states would create their own distinct pattern that is easily distinguishable from that created by a lie or deception. [3] When an fMRI acquires a signal after an individual answers a question, the subsequent brain process measurement can potentially differentiate between an answer’s veracity and its mendacity. [4] In turn, some consider fMRI to be an “unbiased, scientifically-backed way to differentiate a lie from truth telling.” [5] But how reliable is this approach in lie detection?

Modern studies of fMRI-based lie detection often claim that the technology’s accuracy rates are ninety percent or greater. It is important to consider, however, that these studies are conducted in a controlled laboratory setting with willing and reasonably relaxed participants and thus do not reflect the actual conditions of a criminal investigation. [6] In addition, these studies tell us the differences between truths and lies averaged over multiple subjects and trials, but they do not tell us whether the pattern of activation is common with other mental processes or experimental conditions. [7]  

Moreover, if fMRI evidence is permitted in court, it will likely have very persuasive – and perhaps damaging – effects on jurors. A number of studies confirm the idea that individuals tend to be persuaded by the seductive allure of neuroscience and that fMRI possess an “aura of certainty” in the eyes of jurors. These studies raise serious questions concerning jurors’ ability and competency to understand expert scientific testimony. When evidence is highly complex, jurors tend to become confused and base their evaluation of the evidence on heuristic cues – or cognitive shortcuts – that often presume an “implied certainty and authority of science.” [8]

One study conducted by Gurley and Marcus found that participants who were presented with a testimony that was accompanied by a brain scan were nearly twice more likely to render a guilty verdict compared to a testimony that was not accompanied by a brain scan (37% vs. 19%). [9] Another study showed that 75% of participants reached a guilty verdict when presented with fMRI evidence, while 45% of participants reached a guilty verdict when presented with polygraph evidence. [10] These studies highlight how the authority of science and neuroimaging can mislead jurors into believing that the information from these scans is entirely reliable and valid. Of course, progress in the use of fMRI will eventually lead to greater reliability and validity of neuroscience-based lie detection. Nevertheless, even if such technology one day becomes perfectly accurate and unbiased, many would still argue that it constitutes an ethical threat to individual liberties.   

Despite the growing capabilities of neuroscience and technology, the neuroscientific and legal communities have a duty to uphold and safeguard  individuals’ fundamental rights. The Fourth Amendment, which serves to “protect personal privacy and dignity against unwarranted intrusion by the State,” is undoubtedly relevant to this debate. Many would argue that evidence obtained from fMRI-based lie detection violates the Fourth Amendment’s “search and seizure” clause, which protects individuals from overly intrusive searches of their person. [11] In Kyllo v. United States (2001), the court rejected the warrantless search of a suspect’s home using a thermal-imaging device that gathers information about the internal state of a private space without physical intrusion. This can be seen as similar to the way neuroimaging scans obtain information about the internal state of an individual’s mind.   

Brain-scan technologies are improving, but there is still a lot that needs to be considered before allowing them as evidence in the courtroom. Even if this technology one day becomes perfectly reliable and valid, enforcement agencies will need to decide whether or not the needs for justice trump privacy concerns. The thoughts and memories inside our head have always been seen as private; are we ready to relinquish them and allow them to be used as potent information in court?  

[1] “fMRI and Lie Detection.” The Macarthus Foundation Research Network on Law and Neuroscience, February 23, 2016. Accessed January 26, 2018. http://www.lawneuro.org/LieDetect.pdf
[2] Amirian, Justin. “Weighing the Admissibility of fMRI Technology Under FRE 403: For the Law, fMRI Changes Everything – and Nothing.” Fordham Urban Law Journal, 2015. Accessed January 26, 2018. http://ir.lawnet.fordham.edu/ulj/vol41/iss2/1/
[3] Ibid.
[4] Langleben, Daniel D., and Jane Campbell Moriarty. “Using Brain Imaging for Lie Detection: Where Science, Law and Research Policy Collide.” Psychology, public policy, and law : an official law review of the University of Arizona College of Law and the University of Miami School of Law, May 1, 2013. Accessed January 26, 2018.  https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3680134/
[5] Calderone, Julia. “There Are Some Big Problems with Brain-Scan Lie Detectors.” Business Insider UK, April 19, 2016. Accessed January 26, 2018. http://uk.businessinsider.com/dr-oz-huizenga-fmri-brain-lie-detector-2016-4?r=US&IR=T
[6] Kraft, Calvin J., and James Giordano. “Integrating Brain Science and Law: Neuroscientific Evidence and Legal Perspectives on Protecting Individual Liberties.” Frontiers in Neuroscience, November 8, 2017. Accessed January 26, 2018. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5682320/pdf/fnins-11-00621.pdf
[7] Ibid.
[8] Ibid.
[9] Gurley, J. R., Marcus, D. “The Effects of Neuroimaging and Brain Injury on Insanity Defenses.” Behavioral Sciences & the Law, 2008. Accessed January 26, 2018. https://www.ncbi.nlm.nih.gov/pubmed/18327829
[10] McCabe, David P., Castel, Alan D., and Matthew G. Rhodes. “The Influence of fMRI Lie Detection Evidence on Juror Decision-Making.” Behavioral Sciences and the Law, July 12, 2011. Accessed January 24, 2018. https://pdfs.semanticscholar.org/e44c/8f6dba5ec4fc85cb6982014ca52785c50dbb.pdf
[11] Ibid.
Photo Credit: Science Line http://scienceline.org/2008/11/ask-intagliata-lie-detection-fmri-brain-scan/

The opinions and views expressed through this publication are the opinions of the designated authors and do not reflect the opinions or views of the Penn Undergraduate Law Journal, our staff, or our clients.