02/03/2016 11:03 PM AEDT | Updated 03/03/2016 7:53 AM AEDT

Neuroscience Has An Important (But Complicated) Place In The Courtroom

Verdicts in violent crime cases can hinge on brain science.

Shutterstock / Bernhard Lelle
A brain scan.

As our understanding of the brain advances, neuroscience is coming to hold an increasingly important but complicated place in the courtroom. 

In more than 1,500 court cases in the U.S. between 2007 and 2012, judicial opinions were influenced by brain science evidence -- double the amount from the five years earlier. Of those cases, 40 percent were for capital murder. 

For instance, brain imaging is often used to argue for a lesser sentence, to suggest that the defendant was unable to control his or her actions and therefore should not be held fully accountable. On the other hand, this evidence can also be used to suggest that a person is aggressive by nature and a threat to society. 

Consider the following real-life case: 16-year-old Christopher Tiegreen was a friendly, normal high school student until he got into a near-fatal car collision in 2001 that caused severe head injuries. After Tiegreen emerged from his coma, those around him said that he became violent and unpredictable. About eight years later, he was charged for attacking a woman and her 20-month-old son, The Athens-Banner Herald newspaper reported. 

During Tiegreen's trial, his lawyer argued that he was mentally incompetent and a neuropsychologist testified that Tiegreen suffered severe brain impairment, according to the American Bar Association. The jury, however, declared Tiegreen competent. 

“I thought the legal system had ... better sense,” Tiegreen's mother Laura Howell, then a doctoral candidate in clinical psychology, told ABA. “There’s a big crack that people with brain injuries fall into. It’s so narrow in the legal sense that it doesn’t leave room for people like Christopher.”

It's not uncommon for traumatic brain injury, which is often the result of car accidents or sports injuries, to result in aggression. Some research suggests, for instance, that there may be a link between domestic violence among NFL players and head injuries

Cases like these illustrate some of the challenges of bringing neuroscience into the courtroom -- and, more broadly, the complex relationship between the brain and behavior. 

At a Fordham University Law School symposium on Friday, “Criminal Behavior and the Brain:  When Law and Neuroscience Collide,” legal and brain science experts came together to discuss issues in the intersection of brain science and the law.

Drawing on insights from experts at the symposium, here are four benefits and challenges to bringing neuroscience into the courtroom.

1. Brain science evidence can offer an indication of aggressive tendencies. 

Rockefeller University neurobiologist Dr. Donald Pfaff explained one way that neuroscience evidence can be important in the courtroom -- juries can consider testosterone levels, as high testosterone can cause violent behavior, he said. So, elevated levels in the brain may be an important piece of evidence.

In cases of male aggression, it's important to consider the effects of testosterone on the brain. Animal studies have found that the hormone stimulates aggression, and that mice with less testosterone are less aggressive.

In humans, testosterone can predict male aggression as the hormone elevates activity in aggression-inducing neurons in the brain. Increased rates of homicide have been linked to high testosterone levels.

"The very rapid actions of testosterone in the brain could trigger compulsive acts of aggression," Pfaff said at the symposium. 

For instance, if a male defendant was taking synthetic androgenic hormones that increase testosterone levels, this evidence could be used to argue that he was not able to control his aggressive behavior and therefore should not be held fully accountable.

2. Neuroscience may help us to construct a better insanity defense.

The insanity defense is a challenging and divisive legal issue. Largely due to the difficulty of proving mental illness, there is widespread disagreement among legal professionals about its validity. 

"Constitutional questions abound about whether there is even a right to the insanity defense," Dr. Jane Moriarty, a professor of law at Duquesne University School of Law, said during the symposium. 

Moriarty explained that the vast majority of people are legally responsible for their actions -- it's possible, however, that some people should not be.

What does it mean to not be responsible for your own actions? Do mental illnesses or aggressive tendencies -- or severe brain injuries -- mean that a person cannot control their behavior? The insanity defense must answer these complicated questions about free will and the relationship between the mind and the brain.

“If we can reconstruct an insanity defense that makes sense, we’ll see that some people are not [legally responsible] for their actions,” she said. 

The major challenge is finding adequate proof of severe mental illness. Neuroscientific evidence may one day help us to construct a more sound insanity defense, according to Moriarty. 

"Neuroscience can illuminate the relationship between brain injury, cognition and volition," she said. 

3. Brain images may raise more questions than answers. 

Research has shown that judges and juries tend to be impressed by scientific-looking evidence -- and what looks more scientific than a brain scan? 

Images of the brain “lighting up” used in an attempt to indicate pain, aggression or mental illness may impress a jury, but they don’t necessarily say much about how or why a crime was committed. This has been referred to as the “Christmas Tree Effect." We're impressed by the images, but we don't necessarily know what they mean.

“Brains don’t kill people. People kill people."Dr. Ruben Gur, professor of psychiatry and neurology at the University of Pennsylvania

It can be difficult to use evidence of brain activity patterns to draw conclusions about an individual's behavior. Certainly, it's not enough to suggest that an individual didn't know what they were doing when they committed a violent act, according to scientists. There are a number of other complex factors to be considered. 

"Brains don’t kill people. People kill people," Dr. Ruben Gur, a professor of psychiatry and neurology at the University of Pennsylvania, said at the symposium.

4. Right now, neuroscience isn't entirely ready for the courtroom. 

Courts are already admitting neuroscientific evidence in many criminal cases. But as the experts at the Fordham Law conference noted, there's reason to exercise caution when using this evidence. While we can point to fMRI that show what's going on in different parts of the brain, it can be difficult to draw behavioral conclusions based on this evidence. 

"Whether people think the science is ready, it's coming in," Dr. Deborah Denno, director of the Neuroscience and Law Center at Fordham Law Center, said.  

For many years, courts have allowed in psychiatric evidence of mental illness. Denno argues that, with caution, courts should include neuroscience evidence as much as psychiatric evidence.

Gur echoed this sentiment, while also expressing caution about ensuring the quality of the evidence. 

“As long as neuroscientists can testify with confidence that whatever results they got are scientifically acceptable," he said, "it is really up to the judge and jury whether or not they think this is informative."

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