LONDON—The tantalizing prospect of using a brain scanner to determine whether a witness is lying, or a genetic analysis to determine whether a murder suspect is predisposed to commit violent crimes, are premature and unrealistic, according to a new report on neuroscience and the law presented today by the U.K. Royal Society. But neuroscientists might be able to provide evidence for determining whether head injuries are accidental, and whether a violent offender is likely to strike again.
As neuroscience advances, it's easy to see why lawyers are tempted to bring its tools into play on their clients' behalf, the report's authors say. "Neuroscience is engaged in understanding behavior and the law is engaged in regulating behavior," experimental psychologist Nicholas Mackintosh of the University of Cambridge, who headed the Royal Society's working group on neuroscience and the law, said at a press briefing last week. Although it's not known whether lawyers have brought mental health reports or brain imaging into U.K. courtrooms as evidence, mental health is used as a defence about 200 times per year in the United States, the report noted, especially in murder trials where the defendant may receive the death penalty.
One useful application of neuroscience in the courtroom would be the ability to detect lies by using functional magnetic resonance imaging (fMRI). But at best, Mackintosh said, such imaging might be able to detect deliberate lies; it would be useless if a witness truly believed that he was telling the truth. That limitation hasn't stopped at least two U.S.-based companies from marketing such lie detectors, however, and "we take a singularly skeptical view of that," Mackintosh said. "Neuroscience, although very promising, is very young."
Legal expert Roger Brownsword of King's College London warns that, like forensic genetic evidence, neuroscientific evidence might be subject to "facile translations" by lay juries or the media. "The perceptions of jurors might be rather dangerous unless they've been tutored in what the science is," he said. Juries, for instance, could be too impressed by brain images presented in the courtroom if they don't understand their limitations.
The authors recommended that law schools and court systems do more to build "bridges" between scientists and those involved in the law. U.K. law schools, for instance, could provide courses on neuroscience like some U.S. law schools such as Yale University already do.
One area where Mackintosh said neuroscience does hold potential for providing "hard evidence" is in the area of risk assessment: determining which criminals, if released, are likely to reoffend. For instance, a gene that codes for monoamine oxidase (MAOA) has been touted as the "violence gene" because many violent criminals who were abused as children have one form of the gene. Although other genes and environmental factors are certainly involved, Mackintosh said, "If this gene even slightly increases the probability of reoffending, then that's what risk assessment is all about," he says. "It's at least something worth thinking about." All the same, he noted, "risk assessment is a risky business and is notoriously inaccurate."
Most neuroscientists and the Royal Society, however, reject the idea that "having a psychopathic brain" is a general defense against criminal charges. "It doesn't force you to behave in a criminal way," Mackintosh said.
Another question the report examined is the age at which children should be held fully responsible for crimes. In Britain, the age of criminal responsibility is 10 years old—one of the lowest in the world. This young age has been controversial in the past, particularly in several recent murder cases involving children, and, more recently, the spate of riots in August. While the Royal Society didn't take a position on what the age should be, Mackintosh said that "the science certainly suggests that a 10-year-old brain is immature in important respects. It also suggests there is huge individual variation," and that therefore other factors should be considered. Perhaps, he added, "there should not be an arbitrary cutoff age for criminal responsibility."
Other ways in which neuroscience might be closer to bearing fruit in the courtroom are in determining whether a baby's head injury is accidental or a result of shaken baby syndrome, Mackintosh said. Pathologists are more or less agreed on which symptoms constitute evidence of shaking in a baby more than 6 months old, but it is controversial whether these same criteria can diagnose abuse in younger infants. Researchers are also studying whether brain scans could one day be used to determine whether the amount of pain a person reports is actually being felt, or if that person is malingering for the purpose of getting government benefits. Mackintosh cautions that reported pain does not always correlate with the actual extent of an injury and many other mental phenomena are coming into play.