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Can Neuroscience Determine Guilt or Innocence?

As our understanding of the human brain grows more sophisticated, it is changing how courts determine culpability.

ByMo CostandiNOVA NextNOVA Next
Can Neuroscience Determine Guilt or Innocence?

In July 2009, a 59-year-old Welshman named Brian Thomas strangled his wife Christine to death in the middle of the night while the couple were vacationing in their camper van. There was no question he did it, but he was acquitted of murder the following year and walked away from his trial a free man.

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A retired steelworker and father-of-two, Thomas was, by all accounts, a devoted and loving husband. He also suffered from a variety of ailments. As the jury at Swansea Crown Court heard, he had a chronic sleep disorder called automatism ever since childhood, and he had been taking three different prescription drugs to treat his depression and hand tremors, a symptom of his Parkinson’s disease. He stopped taking them before the vacation because he believed that they reduced his sex drive.

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An illustration of the connections within a brain affected by Parkinson's disease

Thomas was, however, unaware that sudden withdrawal from the antidepressant can cause vivid dreaming or that the Parkinson’s drug inhibits rapid-eye-movement sleep, during which dreaming occurs. On that fateful July night, he had a violent nightmare, possibly triggered by an earlier encounter with a group of troublesome teenagers. As the couple lay asleep in bed, he dreamt that a man who had broken into the van and was attacking his wife, and he grappled with him. When he awoke, he saw Christine lying dead, realized what he had done, then called the police to report the killing.

Although extraordinary, the case is not unique. In September of last year, for example, a Swedish man named Mikael Halvarsson was convicted of rape but his charges were overturned. The appeals court heard that he suffered from sexomnia, a rare condition related to sleepwalking, which causes people to engage in sexual behavior while they sleep. Because of this, it was ruled that Halvarsson—like Thomas before him—should not be held responsible for his actions.

Criminal trials often require proof of a guilty mind, or the intention to act. Neuroscience is slowly changing the way we view ourselves, and some worry that using it to explain human behavior is beginning to erode the idea that we have free will and to absolve us of moral responsibility. Neuropsychologists and members of the legal profession gathered at a

multidisciplinary conference at Swansea University late last year to discuss how brain research is beginning influence the criminal justice system. While adoption of neuroscience in the courtroom has been gradual, there’s increasing evidence that it will underpin many legal proceedings in the near future.

Blaming the Brain

The seemingly improbable argument that “my brain made me do it” does sometimes stand up. There is, for example, the widely reported case of the man with a frontal lobe tumor that turned him into a pedophile , and we now know that the drugs used to treat Parkinson’s disease can cause compulsive behaviors such as over-eating, hyper-sexuality, and gambling and shopping addiction due to their effects on the brain’s reward system.

Sometimes, though, it does not. Diminished capacity can sometimes lead to harsher punishment. “By giving us a better understanding of the mind, I think neuroscience will actually expand the scope of responsibility,” says Jennifer Chandler , an associate professor of law at the University of Ottawa.

She cites examples of how someone with diminished capacity could nonetheless be seen to be responsible for their criminal acts in the eyes of the law, such as a patient with schizophrenia who acted violently or someone with narcolepsy or epilepsy who kills or harms others in a car accident after failing to take their medication. In cases such as these, the defendant is considered to have some insight into and control over their actions. They know the potential consequences of not taking their medication and so could be considered negligent for failing to avoid the foreseeable risk of harm.

“Responsibility might become a kind of prior negligent failure to avert later actions,” Chandler says. “We may find ways to hold incapable people responsible by looking back to earlier times when they seemed capable and made risky decisions that contributed to their incapacity and dangerous behavior later on.”

Trauma’s Role

Huw Williams , associate professor of clinical neuropsychology at the University of Exeter, emphasizes that criminal behavior is often associated with traumatic brain injury (TBI). TBI is a major cause of death and disability, and often occurs because of repeated blows to the head which causes lesions as brain’s delicate tissues slide past each other. This often affects the dorsolateral prefrontal cortex, a region which plays an important role in so-called executive functions, leading to changes in mood, thought processes, decision-making, and social behavior.

TBI is much more prevalent among prisoners than within the general population, and prisoners with TBI are at increased risk of committing violent crime. Young people are especially vulnerable. Williams’ own research shows that 11- to 19-year-old male offenders with TBI have more convictions and are more than twice as likely than others to commit a serious violent crime. They are at greater risk for substance abuse and mental health problems . Furthermore, TBI is not only associated with a younger age of imprisonment, but it also makes people more likely to re-offend later on.

It’s impossible to know if TBI actually causes criminal behavior rather than just being correlated with it as there are likely to be many other factors that complicate matters. For example, Attention Deficit Hyperactivity Disorder (ADHD) is associated with criminality, but ADHD medications reduce the rate of criminality in patients. It could even be a two-way relationship, such that injury increases the risk of violence, which in turn causes additional injury that further impacts behavior in a vicious cycle.

This all has implications for sentencing and for rehabilitation. “The medical needs of prisoners with TBI aren’t being met,” Williams says. “Children, in particular, are most likely to be injured but least likely to get the help and support they need.” In a recent report , Williams makes a number of recommendations. There should, he says, be standardized assessments of young people entering the criminal justice system, especially before sentencing, to better identify those young offenders who are most at risk. Prison staff and others within the criminal justice should be made aware of the prevalence of brain injury in the prison population and should liaise with mental health experts to monitor offenders. He also recommends that judges take any history of brain injury into account when handing down sentences.

Developmental Nuance

Yet even in the absence of brain injury, new findings about the teenage brain are already leading some to re-think how young offenders are punished. In England and Wales, the age of criminal responsibility is 10 years, and in the United States, it is 17. Until relatively recently, neuroscientists believed that brain development is complete by about 16 years of age. We now know, however, that while the brain does indeed reach its full size at around that age, its development is far from complete.

The frontal lobes continue to mature until well into the late 20s , and possibly into the third decade of life. The neural circuits involved in functions such as impulse control and decision-making are therefore the very last to mature, and their development is not complete until well beyond what is traditionally thought of as adolescence. What’s more, the reward circuitry in teenagers’ brains is hypersensitive . Together, these findings help to explain what we think of as stereotypical adolescent behavior: taking risks, making bad decisions, and trying hard to impress to their friends.

“Neuroscience holds significant potential to change how young offenders are treated and suggests that we need to take a far more nuanced approach to responsibility,” says Bebhinn Donnelly-Lazarov , a reader in law at Swansea University who organized the conference. “Someone in their early 20s does not lack responsibility in the way that a child does, but we need to recognize that their brain development is still on-going.”

Matters of Interpretation

Courts of law are already beginning to take these matters into consideration. Brain-based explanations of behavior eventually lead to improvements in the treatment of the criminally insane.

Traditionally, the verdict of not guilty by reason of insanity is used very rarely, and courts have discretionary power over what then happens to such defendants. The insanity defense covers a wide variety of conditions, from sleep-walking to diabetes and epilepsy. Defendants whose behavior can be attributed to these conditions can be labeled as insane, but with this label comes a great deal of stigma.

“Neuroscience could be of considerable value in determining whether defendants are truly insane,” Donnely-Lazarov continues. “It should cause the law to move away from these stigmatizing labels such that the law may defer to medical concepts instead of legal ones to define responsibility.”

This raises yet more difficult problems, however, regarding how medical data are interpreted and used. Questions of guilt and innocence may at some stage in the future hinge on neuroscientific evidence, but currently there are major problems with how neuroscientists interpret such data, and those in the criminal justice who might use the information are usually not qualified to evaluate it properly.

It’s unlikely that neuroscience will lead to sweeping reforms in the legal process. Instead, changes will probably occur piecemeal, as our knowledge of the brain advances, and as unusual cases that set new precedents emerge. “Law is a rule-based system, and as such changes in rules of law are needed to accommodate new information,” says Donnelly-Lazarov. “Prosecutors are becoming increasingly willing to consider neuroscientific evidence, so we need to exercise great caution in how we integrate this information as evidence.”

“We’re very far away from criminal statutes saying that a defendant’s brain is in some particular state, but neuroscience will be integrated into the practice of law incrementally and naturally.”

Image credit: Jared Tanner/University of Florida/NIH

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