Advances in neuroscience could transform our criminal justice systems. But the jury is out as to whether "my brain made me do it" will ever be accepted in court.
Grady Nelson had his life spared by a brain scan. In January 2005, after he was released from a Florida prison, where he had served time for the rape of his step-daughter, he returned home to stab his wife 60 times, slash her throat and slam a butcher’s knife into her head. He also stabbed his two stepchildren. The kids survived the attack, but his wife did not. Five years later, a jury in Miami voted against the death sentence for Nelson’s crimes. Instead, they narrowly voted to sentence him to life in prison.
The defence attorneys argued that Nelson had major brain defects that could explain his behaviour. To show this, they submitted as evidence brain activity measurements from a method known as a quantitative EEG (Q-EEG). In a standard EEG, electrodes placed on the scalp measure the electrical activity of the brain. The Q-EEG is similar, except that a computer analyses the data and identifies brain regions of unusual activity. Lawyers had previously tried without success to present such data in court, but this was the first time in the US that a judge presiding over a major case had allowed it.
Clearly, it did the trick. In comments to the press, John Howard, an airport fleet services worker and member of the jury, said he had been about to vote for execution when the Q-EEG evidence had reversed his decision. “The technology really swayed me,” he told a Miami newspaper. “After seeing the brain scans, I was convinced this guy had some sort of brain problem.”
Neuroscientific evidence is increasingly being introduced into legal courts around the world, and novel brain-imaging techniques and interpretations are at the forefront. These approaches may be powerful new tools that help juries and judges determine the culpability of an accused and identify serial criminals. It’s also beginning to influence the way society thinks about sentencing and the treatment of criminals. But learning more about the neurobiological underpinnings of behaviour is also raising uncomfortable questions about free will. On top of all that there are scores of scientists who are critical of the use of such evidence in court.
The tools of neuroscience offer tantalizing glimpses into the inner workings of the brain. For example, a common type of scan called functional magnetic resonance imaging (fMRI) can map brain activity by identifying regions of the brain that have higher levels of oxygen in the blood. Medical doctors use fMRI to determine the effects of head injuries or tumours for instance. But the technique also appeals to lawyers and legal scholars because it seems to show a shortcut to the truth. Humans may lie and cheat, but their brain scans reveal the facts, goes the reasoning.
For example, fMRI has been proposed as a way of telling whether someone seeking compensation for an injury actually experiences chronic pain. US lawyers have already tried to introduce this evidence into the courtroom, but it hasn’t managed to gain any traction yet. In 2008, Sean Mackey, a neurologist and director of Stanford University’s Division of Pain Management, dismissed one of the first attempts, in which fMRI evidence supposedly showed heightened activity in the “pain matrix” of a chemical burns victim seeking compensation from his employer.
These techniques hold promise, but it is dangerous to think neuroscience alone can convict a criminal right now. We like to think of the brain as a giant computer, wired like a well-defined circuit, with electrical signals zipping along neurons in a predictable way, but our brain’s software is complex and sometimes produces surprising results.
What’s more, our brains are highly susceptible to the power of suggestion. Imagining past or future events can affect how we feel right now. During an fMRI scan parts of the brain may light up in response to thoughts as well as action or recalled actions, which means that simply remembering a bout of severe pain could elicit the same effect as feeling the pain. We’re also highly capable of self-deception. “A parent who has shaken and killed their baby may be so horrified by their actions that they convince themselves they were innocent,” says Nicholas Mackintosh, at the department of experimental psychology at the University of Cambridge and chair of a 2011 UK Royal Society report on neuroscience and the law. This can skew fMRI-type lie-detection techniques, which can’t distinguish between people who are telling the truth and those who are guilty but believe they are telling the truth.
Though some are eager to embrace the new techniques in court, others in the legal system are highly skeptical. “The error rates are not very well known,” says Owen Jones, director of the MacArthur Foundation Research Network on Law and Neuroscience, at Vanderbilt University Law School, in Nashville.
Joshua Greene, a psychologist at Harvard University in Boston, is also troubled by the use of fMRI in court to prove guilt. “fMRI differentiates a group who deceived a lot from a group who didn’t, but it’s terrible at identifying whether a person is lying on a single question,” he says. Crucially, says Jones, lab studies of neuroscientific techniques don’t account for real-world situations. “We don’t have good data on how these techniques would operate on people under high-stakes stress, being accused of something that could put them in jail or even executed,” he says.
Neuroscience may have helped Grady escape lethal injection, but most attempts to influence the outcome of a case with neuroscientific evidence have been unsuccessful. “It becomes difficult to pinpoint the relationship between the exact act and the physiological condition,” says Jones. “After all, we don’t know the base rate in society for people who walk around with impairments in their brain who don’t throw their wives out of the window of a tall building.”
But, studies are beginning to highlight potential differences in the brain structures of some criminals. For example, research shows that psychopaths and murderers have physical abnormalities in the amygdala, a part of the brain that mediates feelings like fear and anxiety, and in the prefrontal cortex, which regulates emotions like empathy and guilt. In one small study, Adrian Raine, a criminal psychologist at University of Pennsylvania in the US, showed that the amygdalae of psychopaths are 18% smaller, on average, than non-psychopaths. It is a finding backed up by several other studies.
Research also seems to suggest that some of these differences may start in early childhood. In another study, Raine and his colleagues investigated if children who weren’t afraid of punishment would be predisposed to criminal activity as adults. Other studies have shown that people with underperforming amygdalae don’t fear punishment as much as the average person. To look for answers, Raine used data from a large study of fear conditioning in three year olds born in 1969 and 1970. When the group reached the age of 23, the scientists searched the court records for serious offences, and found that 137 of them (out of 1,795 in total) had been listed as criminal offenders. When Raine compared the offenders with a group of non-offenders, he found that the kids with poor fear conditioning were much more likely to become criminals as adults.
This kind of insight raises the possibility of personalized sentencing, taking into account things like brain abnormalities. A proponent of this approach is David Eagleman, who runs the Initiative on Neuroscience and Law at Baylor University’s College of Medicine in Houston. He dismisses the idea that sentencing criminals based on their brain biology is akin to letting them off the hook. Instead, he argues, “we should be thinking, given that your brain is like this, what can we do to help?”
One of the biggest factors that should be taken into account, he argues, is the age of the accused. The hard cut-offs societies use to determine the age of responsibility for crimes may not be rooted in science but research now shows that certain parts of the brain develop at very different rates. For example, recent studies of the maturation of the prefrontal cortex, which is involved in decision-making processes, suggest that it does not reach full maturity until the late 20s or early 30s. It is a finding that suggests a more subtle way of categorising offenders may be needed; for example biological maturity, a measure of the brain’s plasticity – or how easily it can be modified.
Children’s brains are more plastic than adults, which is why they are able to learn more quickly. Eagleman says neuroscience might one day be able to provide a way to measure the specific plasticity of an individual brain. “If at 20 years of age, someone commits a crime and they have a shrunken frontal lobe and are never going to learn the rules – they might have to be put away for longer.” Mo Costandi, a neurobiologist and science writer based in London, says the new research “will eventually lead to us rethinking the way we punish adolescents.”
Already changes are afoot. On 25 June 2012, the US Supreme Court barred mandatory life sentences for juveniles convicted of murder. The ruling was made, in part, because of this growing mass of scientific research indicating that there’s a difference between adult and juvenile brains, and that juvenile brains develop at different rates. It follows two previous rulings that outlawed the death penalty for juveniles and life sentences for crimes other than murder.
It is a decision that Eagleman says was “long overdue” as juvenile brains are fundamentally different from adult brains. Costandi also maintains it was a “sensible decision” based on recent findings. “Adolescents often make poor decisions that are easily influenced by peer pressure,” he adds. “They also have difficulty controlling their impulses and predicting the consequences of their actions, and all of this has profound implications for how they are treated within the legal system.”
But not everyone is enthusiastic about the prospect of personalised sentencing. “Individualised justice and determination of responsibility are much more costly to society,” says Vanderbildt’s Jones, compared to a one size fits all approach. But Eagleman has heard this argument often. “The numbers work out,” he says. In 2008, for instance, the US government spent nearly $75 billion on correction, most of it on incarceration. “It costs so much to put people in jail and we know it has very low utility – you’ve broken their social circles, their employment opportunities – so they’ll come right back round through that revolving door.”
The changes open up the possibility of other factors being taken into consideration sentencing. For example, roughly a third of US prisoners have a mental illness. Some also have drug addictions. Both are poorly tackled by the criminal justice system, says Eagleman who argues the prison system has become the “de facto mental health system”.
Addiction fundamentally changes the reward system in an addict’s brain, which means he or she no longer responds to the threat of punishment in the same way, says Nora Volkow, the director of the Institute on Drug Abuse at the National Institutes of Health in Bethesda, Maryland. “This explains why the threat of a judicial punishment cannot stop drug-taking,” she says.
That potential for change, even in adult brains, is why people like Eagleman advocate treatment over punishment. His team is running an ambitious programme to improve impulse control in drug addicts. “The brain is like a team of rivals, all of whom are trying to be in control,” he says. “There’s a battle between parts of the brain that want the drug and the parts that are engaged in long-term deliberative thinking and forgoing the drug.”
Eagleman and his colleagues are using real-time neuroimaging feedback to strengthen people’s short-term capacity to resist impulses. He places someone with a drug addiction in an fMRI scanner and shows her a picture of whatever it is she is trying to resist; cocaine, for example. At first, he asks her to allow the craving to proceed, and he measures her brain activity. On a screen inside the scanner, the volunteer watches a bar that represents her craving level. Then Eagleman asks her to try to force the bar to go down. “By squelching that craving, you are strengthening the frontal lobes, which allow you to override impulses,” says Eagleman. “Practicing this over and over means you then know how, even if you don’t quite understand it, to make that bar go down.”
This study is only just underway, and has yet to show if mental strengthening could be a more rational approach to treatment – and prevent habitual reoffending – than imprisonment alone. But it has its supporters. “Anything that can teach people how to control their impulses is a much more sensible way to deal with highly impulsive behaviour than just locking someone up,” says Mackintosh.
In moving towards legal systems that focus as much on treatment as on punishment, societies will nevertheless have to confront an uncomfortable truth, says Eagleman: retribution is built in to our systems. We don’t imprison people just to prevent them from committing a similar crime or to keep society safe, but to punish them and make them pay for what they did.
In the case of Grady Nelson, one of the jurors who voted to imprison him for life rather than execute him did so not because he was persuaded by the neuroscientific evidence of Nelson’s brain abnormality, but because he wanted him to live with the stigma of being a child rapist. It shows that human beings are hardwired for retribution, says Eagleman. “People will give their own resources to punish others even when they’ve not been affected themselves. Even if someone was driven to paedophilia because of a brain tumour, we’ll probably need a minimum amount of sentencing. Just extracting the tumour won’t slake the bloodlust of society.”