Criminal courts in the United States are facing a surge in the number of defendants arguing that their brains were to blame for their crimes and relying on questionable scans and other controversial, unproven neuroscience, a legal expert who has advised the US president has warned.
Nita Farahany, a professor of law who sits on Barack Obama's bioethics advisory panel, told a Society for Neuroscience meeting in San Diego, California, that those on trial were mounting ever more sophisticated defences that drew on neurological evidence in an effort to show they were not fully responsible for murderous or other criminal actions.
Lawyers typically drew on brain scans and neuropsychological tests to reduce defendants' sentences, but in a substantial number of cases, the evidence was used to try to clear defendants of all culpability. "What is novel is the use by criminal defendants to say, essentially, that my brain made me do it," Farahany said following an analysis of more than 1,500 judicial opinions from 2005 to 2012.
The rise of so-called "neurolaw" cases has sparked concerns in the country where brain science first appeared in murder cases.
The Supreme Court has begun a review of how such evidence can be used in criminal cases. But legal and scientific experts nevertheless foresaw the trend spreading to other countries and Farahany said she was expanding her work abroad.
Few cases turn solely on neuroscientific evidence, but scans are thought to have swayed juries in the past. When John Hinckley shot President Ronald Reagan in 1981, his defence lawyers did not dispute that he planned and committed the crime, but claimed he was acting on the impulses of a damaged mind.
They submitted a computed tomography (CT) scan of Hinckley and argued that it showed shrunken regions typical of schizophrenia. The prosecution protested at the scan, arguing that the hi-tech nature of the evidence might lead the jury to put too much emphasis on it. The judge rejected the challenge, and agreed the scan was relevant. Hinckley was eventually found not guilty of the assassination attempt on the grounds of insanity.
Despite the fact that the science is poorly understood and some experts say it is too flimsy to use in court, the evidence has nevertheless succeeded in reducing defendants' sentences and in some cases clearing them of guilt altogether. The number of neurolaw cases rose from 100 to 250 a year over the eight-year survey.