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Brain Scans Gain Momentum as Forensic Evidence, But Jury is Still Out on its Relevance

Samson, Kurt

doi: 10.1097/01.NT.0000269121.90845.69
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  • ✓ Ethicists, neurologists, and legal scholars question the “science” behind psychological and behavioral interpretations of the brain's complex and little-understood topography.

Colorful images of a criminal defendant's brain are becoming a routine part of the evidentiary volley attorneys use to bolster a case if there are any abnormal neurological signs that might be interpreted as influencing their client's alleged behavior.

Defense attorneys have learned through trial and error that functional MRI (fMRI) and expert testimony can persuade juries to be more lenient, and in the past 15 years, many courts have adopted more relaxed standards for the admissibility of brain scans.

But the jury's still out for many ethicists, neurologists, and legal scholars, who question the “science” behind psychological and behavioral interpretations of the brain's complex and little-understood topography.



It's safe to say that once a subject becomes a cover story in the New York Times Magazine, people are paying attention, as is the case with a Mar. 11 feature article on the rapidly emerging field of “neurolaw.”

In the article “The Brain on the Stand,” Jeffrey Rosen wrote: “To suggest that criminals could be excused because their brains made them do it, seems to imply that anyone whose brain isn't functioning properly could be absolved of responsibility. But should judges and juries really be in the business of defining the normal or properly working brain? And since all behavior is caused by our brains, wouldn't this mean all behavior could potentially be excused?”

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Rosen, legal affairs editor of the New Republic, is also a professor of law at George Washington University in Washington, DC. He noted that future scholars and historians may well point to “a little-noticed case from the early 1990s” as the moment when neuroscience “began to transform the American legal system.”

In that trial, defense attorneys for Herbert Weinstein, a 65-year-old advertising executive who was accused of strangling his wife and throwing her body from a skyscraper to make it look like a suicide, wanted to present brain scan evidence showing a subarachnoid cyst. Although the judge allowed the introduction of the images as evidence, the defense was barred from stating that the defendant's cyst might have explained his act, and in an eleventh hour plea bargain, Weinstein's first-degree murder charge was reduced to manslaughter.

Since then, many courts have issued rulings on brain scans as evidence, including a court in Florida that ruled that failure to consider neuroscientific evidence is grounds for reversal in a death-penalty case.

Forensic psychologist Daniel Martell, PhD, who runs a consulting business called Forensic Neuroscience in Newport Beach, CA, has testified in several hundred cases over the last 15 years, including the Weinstein case in which he argued against using the scans.

“I think the judge in Weinstein made a very wise decision in allowing brain images to be introduced as evidence, but not allowing testimony about what they meant. And I think this still holds true today. When it comes to functional neuroimaging, technology has gotten out ahead of the science,” he told Neurology Today in a telephone interview.

“What bothers me is the amount of brain morphometry, or brain mapping, based on MRIs, where the defendant's team compares their client's brain to, say, forty ‘normal’ people, and then draws a conclusion from a very small difference,” he said. “What we know about correlates with behavior is very limited. But if it gets past the judge, juries can often be persuaded, especially in death penalty cases. Sometimes neuroscience tips the scales.”

In his experience, Dr. Martell said, individual judges “are not terribly aware” of the limitations of brain scans. “It's one thing to have an image of the brain, but another thing entirely to say what it means. That's where the chain breaks.”



Still, Dr. Martel said he doubts the controversy will ever reach the Supreme Court. “Instead I think that, incrementally, science will catch up and we will have a much better understanding of behavioral aspects of brain anomalies. I don't think we'll ever find a ‘violence spot' or a ‘murder spot,’ even though there's a lot of work focusing on the amygdala and the frontal lobe. But it really comes down to behavior, and scans are silent on that. Anyone who intuits behavior from a scan is speculating.”

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Forensic psychiatrist Neil S. Kaye, MD, another expert witness, told Neurology Today in a telephone interview that for most attorneys, functional neuroimaging has yet to cross their radar.

“I don't think the [New York Times] article was especially relevant,” he stated. “Functional neuroimaging may be an issue in some high-profile cases — where a lot of money is involved or involving the death penalty — but for most of us out in the field, that's just not happening.”



Nonetheless, he said there are “tremendous flaws and variability” in the laws currently being applied to the admissibility of such evidence.

“I'm not sure how much ground functional neuroimaging will gain in court, either. A lot of jurisdictions haven't accepted it yet, and in this world, challenges under Daubert are more common and many succeed in limiting admissibility. If anything, I think that it's getting even more difficult to introduce such evidence. Juries are getting more skeptical. There's absolutely a place for neuroimaging in the courtroom, but I think we have to be very careful about it.”

[In Daubert, the Supreme Court ruled that scientific evidence need not be 100 percent reliable to be admitted in trial. See “Lowering the Bar for Scientific Evidence.”]

Medical “experts” also lack the leeway they once enjoyed on the stand, said Dr. Kaye, who has authored over 60 publications and presented over 200 lectures on the subject of forensic neuroscience.

Specialty societies like the AAN and the American Academy of Psychiatry and the Law, he added, play an important role in leveling the playing field for advocates and opponents of neuroimaging in trials.

“Professional medical societies are making sure that their members and other experts don't testify to junk science or overstep the facts.”

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“This isn't about the accuracy of neuroimaging tools, it's about the accuracy of what's being measured,” noted Paul Wolpe, PhD, senior faculty associate at the University of Pennsylvania's Center for Bioethics.

“Even a perfect brain imaging technique may not answer the question of why someone does something. One person with a brain anomaly may go out and kill someone while another person with the exact same anomaly is lawful. What does it mean? A functional anomaly doesn't tell us anything. There are as many interpretations as there are questions about them.”

He told Neurology Today in a telephone interview that the Supreme Court has ruled against the admissibility of polygraph evidence, even when the accuracy is as high as 95 percent, and the accuracy of behavioral interpretations of brain scans falls far below that number.

However, given the number of courts being asked to rule for and against neuroimaging evidence as it becomes more advanced, it is only a matter of time before some of these questions have to be answered, according to Dr. Wolpe, who is also president of the American Society for Bioethics and Humanities. He pointed to another major legal issue waiting in the wings: How will the Fifth Amendment's guarantee against self-incrimination apply to evidence culled from a defendant's own brain?

“At some point in the near future, the Supreme Court will have to decide whether brain images are testimony and, if so, what protections an individual is afforded under the Fifth Amendment. I think it will be fairly soon — within ten years.”

But even though brain scan images are “particularly persuasive” to juries, Dr. Wolpe said the competing medical expert witness system is effective.

“It works. Just look at the O.J. Simpson trial. We've already seen how easily a good defense attorney can convince a jury to question the veracity of DNA samples, and brain images are even more complex. Fortunately we're beginning to think about these issues fairly early in the development of this technology,” he noted.

“I don't think anyone is arguing that neuroimaging is ready for prime-time yet. And remember, you can't really coerce someone into submitting to a brain scan. All they have to do is move their head.”

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In 1993, the U.S. Supreme Court held that admission of scientific evidence was not restricted to whether or not it is generally accepted by the scientific community.

In Daubert v. Merrell Dow Pharmaceuticals, the justices provided judges greater leeway in accepting or rejecting admission of such evidence. Although relevant, general acceptance is no longer a necessary precondition. Instead, consideration may include whether a procedure or theory has been peer reviewed, has an error rate, and whether there are accepted standards for the technique.

But of paramount legal importance, the high court held that scientific evidence need not be 100 percent reliable to be admitted. Instead, anything that can alter the likelihood of a material fact is potentially admissible. That leaves it up to juries to decide how much weight such evidence deserves.

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• Rosen J. Neuroscience: The Brain on the Stand. New York Times Magazine, March 11, 2007.
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          • Carter S. Neuroimaging and the ‘complexity’ of capital punishment. February 27, 2007. Notre Dame Legal Studies Paper No. 07–03.
            ©2007 American Academy of Neurology