News When a child commits a crime, a brain scan could tell if they can be held responsible for their actions Brain scans may help court decide criminal responsibility Lawyers may soon be able to offer a defence of immaturity based on an accused individual's own brain scan A FEW years ago, 17-year-old Christopher Simmons was convicted of breaking into Shirley Crook's house in St Louis, Missouri, tying her up and throwing her off a bridge. The evidence was overwhelming and Simmons confessed to the murder. When the jury recommended a death sentence, Simmons's defence referred to scientific papers that suggested a the brain of a typical 17-year-old was not yet fully mature. Not only did Simmons escape the death penalty, the US Supreme Court changed the law so that only those over 18 can face death row. Now neuroscientists claim we are closer to being able to estimate brain maturity using brain scans, which might prompt lawyers to offer a defence of immaturity based on an accused individual's own brain scan. Nico Dosenbach's team at Washington University School of Medicine in St Louis reckon they can predict how old a person is using a 5-minute brain scan. The idea is based on the fact that brain structure changes as we age. For example, the brain's grey matter peaks in childhood and is then pruned throughout adolescence. White matter, which forms the connections between brain regions, steadily increases, eventually levelling off (see diagram below). As we age, parts of the brain that are further apart are better connected and better able to communicate. "The short connections get weaker and the longer ones get stronger," says Dosenbach. His team used functional MRI to measure brain activity in 195 people aged between 7 and 30. "If you see the same regions of the brain are active in sync, it's evidence that they're connected." The group tracked those changes, which levelled off at around age 20. After feeding the information into a computer, they were able to predict the chronological age of other individuals based on a 5minute session in the scanner. "The machine can predict with 92 per cent accuracy whether a brain belongs to an adult (over 25) or a child," says Dosenbach (Science, DOI: 10.1126/science.1194144). "The findings are going to make a big splash," says Jay Giedd at the National Institute of Mental Health in Bethesda, Maryland. He points out that as well as helping to diagnose developmental disorders, such a scan could, in theory, be used to get a defendant off the hook based on the immaturity of their brain. Other aspects of brain development, such as understanding how brain connectivity typically changes with age, would also need to be taken into account to determine whether the maturity of an individual's brain matches their actual age. The age of criminal responsibility is already a contentious issue. In the US alone the age at which a person can legally be tried as an adult ranges from 7 to 18, depending on the state. In Scotland the age is being raised from 8 to 12, and in England a group of neuroscientists, psychiatrists and legal professionals are campaigning for a rise in age of responsibility, saying 10 is too low. "We know the brain of a 10-year-old is extremely immature compared to an adult, both structurally and functionally," says Sarah-Jayne Blakemore at University College London, a signatory on a letter being prepared for the Law Commission of England. "Our argument is that when people make a legal ruling [for children of this age], they should take into account that the brain is very immature." Others argue that by the age of 10 a child understands the difference between right and wrong. "A child at the age of 2 knows not to bite someone," says Arthur Toga at the University of California, Los Angeles. "It's not to do with knowing the difference between right and wrong," counters Blakemore. The group argue that because the prefrontal cortex (PFC) is the last part of the brain to mature, a child is unable to understand the long-term consequences of their actions. A child may be unable to suppress potentially dangerous behaviour, and make bad decisions. "It's the PFC that stops you doing 200 miles an hour down the motorway," says Blakemore. "The ability to do these things changes a lot during adolescence, and courts need to take this into account when deciding punishments," agrees Giedd, who is not part of the campaign. A brain scan could aid this decision. So how do you decide what the age of criminal responsibility should be? Although Blakemore's cosignatories make the case for raising the age from 10 they say further research will be needed to determine what it should be. "The idea that the brain suddenly becomes adult is misleading because the brain is plastic and continues to change throughout adulthood," says Blakemore. Dosenbach's study suggests the major changes to the brain's structure don't start to level off until around age 20. But is this a realistic age of criminal responsibility? "If the standard is 'as good as it's going to get' then the age of criminal responsibility should be set around 20," Giedd says. "But it's a matter of whether we need the brain to be at its completely mature state." Another option is to have a sliding scale of responsibility for adolescents, decided on a case by case basis. In England and Wales, 10 to 14-year-olds used to be assessed this way, says barrister Paul Mendelle of 25 Bedford Row Chambers in London. The law changed after two 10-year-old boys were convicted of the torture and murder of 2-year-old James Bulger. "Based only on my professional experience the sliding scale seemed to work best," says Mendelle. "Some are able to appreciate the consequences of what they've done, but children are often just ignorant of the consequences of their actions." In these assessments, a brain scan could come in handy, he adds. Even if someone's brain could be deemed physically "immature", it's not yet clear how age-related changes in volume of grey and white matter tally with a person's behaviour. "We know that the brain is maturing physiologically," says Owen Jones, director of the Law and Neuroscience Project at Vanderbilt University in Nashville, Tennessee. "But that doesn't necessarily come hand in hand with functional maturity, which is what the legal system is concerned with." Toga agrees: "There is no hard and fast rule of development, and there will always be some degree of variation depending on genetics, environment, experience, diet and stimulation." Despite difficulties linking brain maturity to behaviour, it is likely lawyers will attempt to use brain maturity scans in the courtroom. Nita Farahany at Vanderbilt University assessed 700 US legal cases between 2004 and 2009, including 45 juvenile cases. Of the adult defendants 16 per cent introduced brain scans which pointed towards mental illness and tumours, in an attempt to diminish responsibility for a crime. In the US a neuroscientist can already be called to testify on behalf of a child and present peerreviewed research to make the case that adolescent brains are immature. "It isn't always a winning claim, but in several cases it was successful in decreasing the sentence," says Farahany. For better or worse, it is likely that individual brain scans for assessing brain maturity will be used in the courts in the next few years, says Farahany. Not yet responsible "Individual brain scans for brain maturity will likely enter the courts in the next few years" ~~~~~~~~ By Jessica Hamzelou © 2010, New Scientist, Reed Business Information UK, Ltd., a division of Reed Elsevier, Inc. All Rights Reserved. Copyright of New Scientist is the property of Reed Business Information and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use.
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