fMRI on Trial

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If neuroimaging can reliably discern truth from falsehood, should brain scans be admissible evidence in court cases?

Brooklyn defense attorney David Zevin almost made legal history last month by attempting to submit functional magnetic resonance imaging (fMRI) data as evidence that a key witness was telling the truth. Zevin was defending Cynette Wilson, who claimed that the temping agency she had worked for stopped giving her work following her complaint of sexual harassment.

A co-worker at the agency claimed he had overheard Wilson’s supervisor saying that she should not be placed on jobs because of her complaint, so Zevin had the co-worker undergo questioning about the incident during a brain scan by Cephos, one of several American companies that claim they can reliably use fMRI to establish whether somebody is telling the truth or lying. fMRI measures the changes in cerebral blood flow that are related to brain activity. Some researchers claim that they can distinguish between the activation patterns associated with lying and telling the truth and, therefore, that the technique can be used for reliable lie detection.

fMRI data have actually been used in the court room before, one notable example being a controversial 2008 trial in India, in which a conviction was based on brain scan data that suggested the suspect was present at the crime scene. But Zevin’s was the first attempt to submit such data for the purposes of lie detection, and as such the case was considered a landmark. In the end, presiding judge Robert H. Miller decided to exclude the fMRI data, on the grounds that it contravenes the jury’s right to assess the credibility of the witness.

So can fMRI be used reliably for lie detection? A very small number of previous studies suggest that the technique can be used to distinguish between truth and falsehood under controlled and highly contrived experimental conditions. It is, however, by no means clear whether this can be replicated in real-life situations.

fMRI is generally thought to be no more or less reliable than the traditional polygraph test, which measures the changes in various physiological parameters—such as heart rate, blood pressure and skin conductance—that can change when someone is lying. The success rate of the polygraph is only a little higher than would be expected by chance and, according to a report by the National Academies’ National Research Council, the technique cannot be relied upon to give accurate results.

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An important and related issue is memory, with respect to the reliability of eye-witness testimonies. We have known, since Frederick Bartlett’s work in the 1930s, and subsequently from the work of pioneering researchers such as Elizabeth Loftus, that memory is reconstructive, rather than reproductive. In other words, we do not always remember events as they actually happened; instead, our prejudices and biases shape our recollections.