Tuesday, March 10, 2015

Legalize Veritaserum: A Defense of the Use of Neuroimagery in Lie Detection


Like the rest of the country’s coolest kids in high school, I dedicated what some would call an “unhealthy” amount of time to memorizing minute details about the Harry Potter universe.  Among my favorite of J.K. Rowling’s plot-hole-fillers du jour was a potion known as veritaserum, which would compel its drinker to tell truths, and only truths.

In the Harry Potter stories, veritaserum primarily used by unscrupulous school officials and reporters, and specifically banned from use in the Wizengamot (That’s Wizard Court, for those of you who may not have been the coolest kids in your high school.).  It is banned because the Wizengamot fears its occasional unreliability, and that it would supplant the role of its members as a trier of fact.

Now, considering this is only my second year of law school, I haven’t read as many law review articles as most people.  But, I can say to a degree of certainty that there isn’t a single article out there that compares the writing of J.K. Rowling to the jurisprudence of Justice Clarence Thomas.  Believe me, I’ve checked.

The Wizengamot’s logic in banning veritaserum from their legal proceedings mirrors Justice Thomas’s logic in the case United States v. Scheffer, where the Court held that a criminal Defendant did not have a Sixth Amendment right to present lie detection evidence in his defense.  According to Justice Thomas, the introduction of polygraph evidence would “diminish the jury’s role in making credibility determinations.”  This decision built off an existing sentiment in the Brown v. Darcy, the Court held that introducing lie detection evidence would “shroud that evidence in an aura of near infallibility, akin to the ancient Oracle of Delphi.”

Now, fears of admitting polygraph evidence are well founded.  Like veritaserum, there are known limitations to polygraph use, and known ways of countering it.  While countermeasures to the polygraph test are becoming more difficult to implement, a great deal of polygraph analysis involves the skill of the polygraph tester.  Additionally, the polygraph tester could be subjected to interpersonal, or confirmation biases that would lead him to believe that there is deception when deception does not exist.  These failures, and other can be assuaged by utilizing an alternative to the polygraph: the fMRI.

The fMRI works by utilizing the same magnetic resonance imaging commonly used for diagnostic purposes in hospitals and applies that technology to measuring the movement of blood within the brain, also known as hemodynamism.  Hemodynamic movement throughout the brain is peculiar to the particular function that the brain is engaged in – whether that be basic life support, memory recall, cognitive reasoning, or creation of falsehood.  This is based on the indisputable scientific truth that active parts of the brain require more oxygen than passive parts of the brain.

Hemodynamic movements can be measured through the fMRI by monitoring the changing differences in the magnetic properties of blood over time.  This is known as the Blood Oxygenation Level Dependent response, or “BOLD” Response.  The fMRI allows for a dynamic measurement of the body’s BOLD Responses over time, and demonstrates which areas of the brain are the most active, via monitoring distinct hemodynamic movements.

An fMRI’s scan be used to objectively determine factual accuracy in a statement by measuring these distinct BOLD movements.  Here, engaging in deception requires a certain executive function associated with higher levels of problem that is visibly distinct from simple memory retrieval.  As such, comparisons can be drawn between the subject’s BOLD Responses when he is recounting true statements, answering statements known to be false, and finally the statements in question. If similar parts of the brain are activated during the unknown questions as during the known falsehood, that is evidence of falsehood, and vice-versa for true statements.

Rather than measure perspiration, muscle contraction, and heart rate to see the symptoms of a lie, the fMRI can show biological evidence of the lie itself.  Consistent tests have shown that there are distinct hemodynamic movements associated with lying.[1] But we return, of course, to the same problems that plague the Wizengamot’s use of vertiaserum

The fear that the use of fMRI analysis would supplant the role of the jury as the trier of fact. The problem is, juries as a whole don’t perform particularly well at detecting truth.  The most optimistic studies of a jury’s ability to discern truths from lies only has the jury being correct sixty-one percent of the time, and in many cases, the jury is accurate less than half the time.  The reverence that Justice Thomas and others have for using the jury as a lie detector should be considered poorly placed when a jury’s odds of telling whether someone is lying are comparable to the jury’s ability to tell which way a coin will flip.

There is also a fear that the use of neuroimagery for Defendants in criminal cases will unfairly prejudice the jury.  Supposedly, parochial jury members will be so mystified by the colorful images of the brain and technological jargon spouting from expert witnesses’ mouths will cause them to either disregard other evidence, or regard the expert testimony with the same pious reverence not seen since the Age of Pericles.

There is precedent for this argument.  It was used in the Eighties to keep DNA away from jurors, on fears that it would confuse them.  It was also used in the late Nineteenth Century when judges feared that the introduction of photographs involved too much complicated explanation for triers of fact. Both have become a mainstay in today’s courtrooms.

It is also true that neuroimagery has been shown to not have a prejudicial effect time[2] and time[3] again. Studies demonstrate that the use of neuroimagery does not prejudice the jury more than any other kind of expert testimony.  Texas Christian University has referred to neuroimagery as having “selective, rather than a seductive appeal.

The reason that juries aren’t mystified to the point of prejudice by scientific evidence is because those experts can always be tested in the crucible of cross examination. Justice Stevens’ dissent in Scheffer is instructive here when he holds that “reliance on a fear that the average jury is not able to assess the weight of this testimony reflects a distressing lack of confidence in the intelligence of the average American.

We are currently living in a time with the most educated juries in all of recorded history. That alone should be a compelling reason to believe that neuroimagery is certainly more reasonable, and should be infinitely more legal than veritaserum.


Travis Nemmer
Staffer, Criminal Law Practitioner




[1] John G. New, If You Could Read My Mind: Implications of Neurological Evidence for Twenty-First Century Criminal Jurisprudence, 29 J. Legal Med. 179, 182-84 (2008). 
[2] Edith Greene & Brian S. Cahill, Effects of Neuroimaging Evidence on Mock Juror Decision Making, 30 Behav. Sci. L. 280, 293
[3] N. J. Schweitzer, Michael J. Saks et. al., Neuroimages As Evidence in A Mens Rea Defense: No Impact, 17 Psychol. Pub. Pol'y & L. 357, 388

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