By Adam Ho

Behind every word men utter, there is a complex series of processing and integrating information in the brain. For more than a decade, scientists have been exploring the method of using functional magnetic resonance imaging (fMRI) brain scans to detect lies. Despite the growing influence of neuroscience in the legal sphere and its potential for juror-decision making, the use of fMRI scans as a testament for or against the defendant exposes the private, internal state of individuals. This article discusses the values and limitations of the use of fMRI scans to detect lies, a piece of potent evidence that could turn the course of a jury trial. The neural mechanism of how fMRI detects lies will be first explored, which is in tandem compared to the traditional lie detector, polygraph, demonstrating the prospects of using fMRI in forensic cases. The limitations of fMRI will be then discussed with reference to the validity of the experiments raised, the psychology of criminals, and the structure of the society.

The Neural and Physiological Basis of Polygraph and fMRI in Detecting Lies

fMRI uses magnetism to measure the ratio of oxygenated to deoxygenated blood in particular areas of the brain, three-dimensional regions referred to as “voxels” [1]. In the context of formulating a lie, the higher the ratio of oxygenated to deoxygenated blood in a particular voxel, the more likely the specific brain region is responsible for lying. A study shows that the activation of the inferior parietal lobule was specific to truth while activation of the medial and inferior frontal gyrus was specific to lies [2] (See figure 1). The parietal lobules are collectively thought to be vital for sensory perception and integration in humans, while the frontal lobules are thought to be important for voluntary movement, expressive language, and managing higher-level executive functions [3][4]. Therefore, it is understandable how these lobules are involved in conceding the truth and fabricating lies.


Moreover, fMRI eliminates confounding factors, for example, anxiety and stress, when compared to the traditional lie detector - polygraph. This is due to the fact that distress and lying activate separate pathways in the brain seen on fMRI, which may not be distinguished otherwise [5]. On the other hand, a polygraph consists of a physiological recorder that assesses three indicators of autonomic arousal: blood pressure, respiration, and skin conductivity [7] (See figure 2). The use of a polygraph assumes that lying will produce physiological responses that can be differentiated from those associated with non-deceptive answers. Yet, there are no specific physiological responses associated with lying, leading to controversies on the validity of polygraphs [8].

As a result, fMRI could be a promising tool for the detection of lies since it is more immune to the confounding of anxiety and stress, as well as showing relatively higher specificity of the brain regions that are associated with lying, compared to a polygraph.

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Figure 1: An anterior and sagittal view of the brain which shows the average brain regions for 22 subjects during testing. Blue areas represent regions more active when telling the truth, red areas, when lying [6].

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Figure 2: The set-up for a polygraph [7].

The Prospects of Using fMRI as a Forensic Tool

The detection of lies with reference to fMRI is greatly influential in juror-decision making. One study showed that with the evidence of fMRI, up to 75% of participants reached a guilty verdict. Conversely, when presented with polygraph evidence, only 45% of participants reached a guilty verdict [9]. The study highlights how the authority of science and neuroimaging can mislead jurors into believing that the information from these scans is entirely reliable and valid.

The accuracy of fMRI has been further demonstrated in an experiment detailed in another study. In the experiment, participants were asked to secretly write down a number between three and eight. Next, each person was administered the Concealed Information Test (CIT), a test that detects a person's guilty knowledge of a crime [10]. In the meanwhile, participants were either hooked to a polygraph or lying inside an fMRI scanner. Each of the participants had both tests, in a different order, a few hours apart. During both sessions, they were instructed to answer "no" to questions about all the numbers, making one of the six answers a lie. Results show that fMRI was 24% more likely to detect the concealed number than polygraph [11].


The results of the studies shed light on the possible use of fMRI as a forensic tool. Dr. Robert Huizenga, a celebrity doctor known as Dr. H on The Biggest Loser, said that fMRI is “a paradigm shift in how we analyze truth-telling”, highlighting the possible use of fMRI in proving the truthfulness of testimony [12]. But is this really the truth?

Problems to be tackled

Firstly, the setting of the experiment is vastly different from that in the setting of a court. Courts have also pointed out that the motivation to lie may be different in research compared to real-world settings [13]. In the experiment, participants are essentially complying with the investigator's directions. However, when the scan is to be used in the courtroom, the subject will have a personal interest in the outcome of the brain scan, and may employ countermeasures in order to fool the scanner, resulting in an inaccurate brain fMRI scan.

Secondly, the mechanism of fMRI is manipulated by criminals to produce fallacious interpretations. Recent research shows that this task may not be hard, at least not for those who know how to effectively “trick” the scanner. A possible mechanism is through the attachment of emotions to irrelevant information [14]. Moreover, the utilization of fMRI as a forensic tool to prove guilt or innocence infringes on the privacy of an individual. The use of fMRI has raised extensive concerns about privacy interests in thoughts and is believed to be a “mind-reading technology” that exposes the deepest thoughts of individuals [15].

Thirdly, the social structure is slow to change, despite science rapidly making headways. In the US, science-based reforms have yet to make significant inroads among police and other security officials, for example, the use of fMRI in lie detection. However, the US Department of Homeland Security’s Transportation Security Administration still uses nonverbal cues to screen airport passengers for questioning, although it is experimentally shown that no nonverbal cues are reliable indicators of lying [16]. This demonstrates that science is culturally and socially embedded and that fMRI may not be fully implemented in the near future.

Conclusion: Tempering Our Notion of Fairness

The advancement of technology has brought about breakthroughs and hopes for a more unbiased, fair, and rightful verdict. fMRI proves to be a more accurate technology compared to polygraphy, and new technologies might arise in the near future in the detection of lies. Yet, there are a couple of unanswered and thorny questions: Is fMRI brain scan an accurate indicator of whether an individual is lying? Even so, it is justified for one to promote justice at the expense of privacy concerns? The more neuroscience reveals to us, the more one has to temper the notion of what fairness and justice mean, as well as accommodate the social structure to new ramifications.