Skip to main content

Neuroscience Won’t Transform Legal System Any Time Soon, Experts Say

Despite an explosion of research on the use of brain scans and other tools of science to help better determine a person’s guilt or innocence, experts at a AAAS-organized discussion said hopes that neuroscience might transform the legal system are unrealistic for now.

For judges and juries, the fundamental challenge has always been to figure out whether someone is telling the truth. The underlying problem, according to Dr. Steven E. Hyman, director of the Stanley Center for Psychiatric Research at the Broad Institute of Harvard and MIT, is simple enough: “We don’t have access to people’s mental states.”

Without such access, courts and juries have had to rely on indirect methods to assess truthfulness, including psychiatric reports on the defendant, witness interviews, testimony by the accused under cross examination, and even the person’s body language. It is not surprising that there has been a thirst for more objective measures of criminal intent—a genetic test, a scan of certain areas of the brain—that might yield a better understanding of what motivates unlawful behavior, Hyman said.


Dr. Steven E. Hyman | Credit: AAAS

But criminal behavior is proving to be far more complex and difficult to predict than some enthusiasts for neuroscience in the courtroom maintain, he said. “I believe ultimately that our behavior is a production of activity in our brain circuits,” Hyman said. “But I would never tell a parole board to decide whether to release somebody or hold on to somebody, based on their brain scan as an individual, because I can’t tell what are the causal factors in that individual.”


Hyman spoke at AAAS on 25 April in a discussion of “Neuroscience and the Law,” the first event of 2013 in a “Neuroscience and Society” series organized by AAAS in partnership with the Dana Foundation. The event also was sponsored by the International Neuroethics Society and the MacArthur Foundation Research Network on Law and Neuroscience.

Even if a scan shows abnormal activity in a brain region associated with impulse control or regulation of emotions, such imaging provides no more than probabilistic information, Hyman said. It may suggest a correlation between someone’s brain activity and an observed behavior, he said, but it does not prove causation—that some malfunction in a crucial region of a person’s brain made them commit a crime.

Only in the most severe cases, Hyman said, might a brain-altering event be clearly seen as the cause of behavioral changes. He noted the famous case of Phineas Gage, a railroad construction foreman whose brain was penetrated by a large iron rod in an 1848 industrial accident. Gage survived, but subsequently exhibited profound personality changes, including frequent use of profane language, impulsivity, and anti-social behavior.

By contrast, attributing causality to more subtle genetic and environmental influences on the brain remains a difficult challenge. There has been considerable interest, for example, in a gene that produces low levels of an enzyme called monoamine oxidase A (MAOA) in the brain. Studies suggest that the presence of this low-activity version of the MAOA gene, perhaps in combination with other factors such as physical abuse during childhood, could carry an increased risk of aggressive behavior.

This gene already has figured in a court case in Italy, Hyman said, where a defendant’s sentence was reduced based on testimony that he had the gene and was predisposed to violence. The prosecution appealed the sentence, Hyman said, and the appeals court—rather than rejecting the sentence—agreed with the trial court and reduced the sentence by an additional year.


Owen D. Jones | Credit: AAAS

But the findings on the MAOA gene are drawn from population studies, Hyman noted, and it is unclear how averaged data from such studies can be applied to the actions of specific individuals. Except for rare, severe syndromes, Hyman said, behavior is the product of many genes, brain development, chance, experience, and the context of actions.


Such complexity notwithstanding, interest in neuroscience and the law continues to soar. There have been more than 900 publications related to the topic since 1984, with the vast majority of them published since 2005, according to Owen D. Jones, director of the MacArthur Foundation Research Network on Law and Neuroscience and a professor of both law and biology at Vanderbilt University.

Jones said lawyers, judges and juries certainly could benefit from scientific insights on such perennial legal questions as: Was the defendant responsible for the criminal behavior? How competent is the person to stand trial? Is the person lying? What capacity did the person have to act differently? What are the chances he or she will be a repeat offender?

But Jones, like Hyman, cautioned about trying to draw conclusions about individual behavior based on studies of groups. Not everyone with a neurological abnormality or a particular genetic trait will go on to violent criminal behavior.

“There has to be serious effort by lawyers and by judges as well to separate the wheat from the chaff,” Jones said. There must be a “chain of legitimate inferences” from any biological finding to criminal behavior, Jones said. Such inferences are not easily made.

He mentioned the case of a man who threw his former wife out a 12-story window, trying to make her death look like a suicide. A brain scan showed the man had a large cyst impinging on his brain. “We have no idea how many people are walking around with this condition who do not throw their wives out the window,” Jones said. “Causation here cannot be assumed.”

Judge Barbara Rothstein, a visiting U.S. District Judge from the Western District of Washington state and past director of the Federal Judicial Center in Washington, D.C., offered a reality check on how science is used in the courtroom. It is introduced in an adversarial setting, she said. Whatever the nuances of the current research, the job of the experts brought into a case by prosecutors and defense attorneys “is to make the judge or the jury believe that their version of the science is true and correct and should win the case,” Rothstein said. She added, “There is no interest in science as an abstract matter.”


Dr. Steven E. Hyman, Owen D. Jones, and Judge Barbara Rothstein | Credit: AAAS

Neuroscience has been met with skepticism by judges so far, Rothstein said. Unlike DNA testing, for which there was considerable scientific consensus before it was widely used in the courtroom, neuroscience “is reaching the courts in a premature state,” she said. With no consensus on the value of functional magnetic resonance (fMRI) imaging and other technologies, she said, judges often have not even allowed the results to get to the jury.


“When you have a group called ‘No Lie MRI,’ somehow or other that just doesn’t have the ring of real science that makes you want to say, ‘Oh, I guess the jury should hear this,’” Rothstein said. “It isn’t convincing.” Rothstein also noted the different time frames judges must deal with compared to scientists. “We can’t wait around until the experiments finish, until there is a consensus in the scientific community,” she said. Courts must decide cases in the present, based on the best available evidence.

Rothstein and the other panelists agreed that neuroscience may well become an important factor in court proceedings as brain science continues to evolve. “I assume that over a period of years some of this may get to be more reliable,” she said. Hyman agreed. “I think we’re going to understand a lot more,” he said. “But it’s really early days.” Jones called it an exciting time, but “one in which we have to move with deliberate caution as well.”


Earl Lane

Related Scientific Disciplines