The ethical minefield of using neuroscience to prevent crime

On the evening of March 10, 2007, Abdelmalek Bayout, an Algerian citizen living in Italy, brutally stabbed to death Walter Perez, a fellow immigrant from Colombia. Bayout admitted to the crime, saying he was provoked by Perez, who ridiculed him for wearing eye makeup.

According to Nature magazine, Bayout’s defence argued that he was mentally ill at the time of the offence. The court accepted that argument and, although it found Bayout guilty of the crime, imposed on him a reduced prison sentence of nine years and two months.

Bayout nevertheless appealed the judgment, and the Court of Appeal ordered a new psychiatric report. That report showed, among other things, that Bayout had low levels of the neurotransmitter monoamine oxidase A (MAO-A) — an important development given that previous research discovered that men who had low MAO-A levels and who had been abused as children were more likely to be convicted of violent crimes as adults.

Ultimately, the Court of Appeal further reduced Bayout’s sentence by a year, with Judge Pier Valerio Reinotti describing the MAO-A evidence as “particularly compelling.”

Upon a brief review of the scientific evidence, certain glaring problems with the court’s judgment quickly become apparent. Most obviously, the research showing an association between low MAO-A levels and violence tells us nothing about Bayout’s — or any specific individual’s — propensity for violence. Indeed, while a significant percentage of men with low MAO-A levels commit violent offences, the majority do not.

Yet the fact that the court allowed such evidence to influence its verdict suggests that neuroscience, while not eliminating criminal responsibility, might lead courts to conclude that defendants with certain neurological deficits are less responsible than those with “normal” brains.

There is, in fact, a precedent for this, and it’s one that few people question. Adolescents in virtually every country are subject to differential sentencing, and in many cases to an entirely separate system of justice, because their neurobiology renders them less blameworthy, less responsible than adults.

Indeed, while the limbic system, or emotional centre of the brain, is typically mature by the age of 16, the prefrontal cortex, which is associated with one’s capacity to control emotions, is not fully developed, in most people, until the early 20s. Hence according to what’s sometimes called the “two systems” theory, the imbalance in development of the limbic system and the PFC explains the risk taking and emotional behaviour that is characteristic of adolescence. And it justifies our treating adolescents as less responsible than adults.

There are, of course, substantial differences between adolescents and adults with neurological deficits, the most obvious being that most adolescents will outgrow the developmental imbalance. But the basic principle — that people who suffer from neurological aberrations that render them less capable of controlling their behaviour should be held less blameworthy — seems to have swayed the Italian Court of Appeal.

But not just the Italian Court of Appeal. While the “MAO-A defence” has been tried and failed in many courts around the world, recent research led by University of Utah psychologist Lisa Aspinwall suggests that many judges, when presented with neurobiological evidence, are inclined to reduce defendants’ sentences.

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