The Lying Brain

Prospects of fMRI as a Lie Detector

Could fMRI be the new polygraph for lie detection?  Where are we along the developmental path for such a system, and could it ever be implemented in the legal system?  Two researchers from University College London and the University of Parma, Italy, have been asking such questions in a recent paper published in Frontiers in Human Neuroscience.

Cognitive neuroscientists have been investigating the neural basis for complex mental processes like moral beliefs, intentions, self-knowledge, social interaction, and even consciousness itself.  Visual representations of such brain behaviour from fMRI machines are starting to be used in court, and it will not be long before this kind of evidence will be used to prove brain abnormalities in defence of the behaviour of an accused person, according to authors Elena Rusconi and Timothy Mitchener-Nissen.

It is not great a stretch of the imagination to see the use of fMRI in the courtroom progressing to state-of-the-art lie detection for malignancy and deception in criminal cases.  But how reliable is it, and what ethical and legal questions will it raise?  This “brave new world” of deferring to the authority of brain science in our legal system is an issue of fundamental importance.

The study authors point out that in the private sector, fMRI is already being marketed as a lie detection tool.  The website (no lie MRI) boasts “unbiased methods for the detection of deception and other information stored in the brain”.  Sporting images of the brain on its home page, with representative activity in the medial frontal gyrus highlighted as a “lie”, this company boldly asserts itself as the modern answer to the polygrapher, using “the first and only direct measure of truth verification and lie detection in human history!”Another company, Cephos Corporation, also offers fMRI lie detection for use in legal proceedings, employment screening, and national security investigations, in addition to its forensic DNA service.

In the corporate world, fMRI lie detection services may well prove attractive to executives who need to maintain a high level of trust in their executive team.  Screening current and future employees could be seen as astute business management.  In the more conservative legal context of the courts, however, the use of fMRI as a lie detection tool is still a long way from being viable.  Summarising some of the basic difficulties, Rusconi and Mitchener-Nissen point out that “protocol design determines how fMRI evidence can be interpreted, full compliance is required from paticipants, and the final evidence reflects choices, assumptions and data transformations based on current scientific standards and consensus criteria but also on publication strategies.  Finally, not everybody can undergo fMRI.  So the question remains, can its potential contributions as a lie detector outweigh its intrinsic limitations?”

The Lying Brain

Most of us believe we are good at knowing when someone is lying.  We can pick up the cues in body language, content, voice quality and eye gaze.  However, Rusconi and Mitchener-Nissen point out that we can tell the truth from lying only about 54% of the time (slightly better than chance), even in the case of police, lawyers and psychiatrists.  The ability to lie, however, comes naturally to us (unless we have damage to the orbito-frontal region of our brain or have autism) and seems dependent on localised orbito-frontal neural circuits.

The authors explain that “within a basic cognitive neuroscience perspective, fMRI research on deception can indeed aspire to provide correlation maps that possibly reflect the difference between deceitful and truthful responses.”  However, the generation of reliable “maps” that mark deception is a multi-modal task involving other techniques with complementary inferential power.  Functional MRI alone cannot provide robust and compelling evidence of an activated deception neural substrate.  Complicating this is the fact that compliance by the participant under fMRI scrutiny is vital for valid results.  In a basic research setting there is no reason for a participant to be noncompliant, but in a criminal forensic setting there is every reason for the subject to adopt countermeasures aimed at producing false results.  Fooling the fMRI machine would become a popular criminal mind game, complete with specialist training for those on the defence.  Laboratory experiments that claim up to 90% accuracy for lie detection are unlikely to be replicated in a real-world application to criminals.


Privacy rights and the rights to silence, thoughts, and a fair trial are all brought into focus as areas of potential constitutional and human rights violations when considering fMRI evidence of a subject on trial.  The cost also of imaging and the staffing and training required are likely to prove prohibitive within the justice system.  Then there are questions as to the validity of assessment algorithms, who will interpret them, and how such an interpretation would be verified.  Moreover, as new technology becomes available, will those who maintain their innocence seek to be re-tested with new technology and new algorithms, placing a further burden on the criminal justice system?

Finally, will the introduction of fMRI testing for truthfulness be acceptable to society?  Will people accept “mind reading machines”?

Rusconi and Mitchener-Nissen conclude that “our societies have developed to both accept and respect an individual’s right to keep secrets, and in so doing they do not seek to override human beings’ evolved capacity to keep secrets, for a society where individuals are denied secrets is not a human society as we know it. The developers and proponents of fMRI testing must respect this fact and engage society in their research as it progresses. Otherwise they may find they successfully negotiate the frying-pan of scientific and technical challenges in perfecting fMRI testing only to be consumed by a fire of legal, ethical, social, and political opposition.”

Rusconi, E., & Mitchener-Nissen, T. (2013). Prospects of functional magnetic resonance imaging as lie detector. Frontiers in Human Neuroscience, 7, 594. doi: 10.3389/fnhum.2013.00594


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