Last month the Supreme Court ruled that teenagers under age 18 who commit premeditated murder cannot be executed. The court based its ruling in part on recent studies that found that the frontal lobes of teenagers were not sufficiently developed, making them not fully responsible for their actions. To justify its ruling, the court majority adopted many of the arguments put forth in an amicus brief sponsored by the American Medical Association and the American Psychiatric Association, among others.
That brief argued that recent neuroimaging studies had found that the "brain's frontal lobes are still structurally immature well into late adolescence. The prefrontal cortex (which.is most associated with impulse control, risk assessment, and moral reasoning) is 'one of the last brain regions to mature.'" Consequently, the amicus brief concluded the evidence "based upon studies of normal adolescents, leads to the conclusion that normal adolescents cannot be expected to operate with the level of maturity, judgment, risk aversion, or impulse control of an adult. Adolescents cannot be expected to transcend their own psychological or biological capacities. However, an adolescent who has suffered brain trauma, a dysfunctional family life, violence, or abuse cannot be presumed to operate even at standard levels for adolescents."
Naturally, death penalty opponents and child advocacy organizations hailed the court's decision. But this diminished capacity argument could well play out in disturbing ways.
Already the immature teen brain argument has been used by legislators to impose various restrictions on teenage drivers, including limits on times they can drive, the number of passengers they can carry, and their use of mobile phones. That may appear reasonable; after all, teenagers do account disproportionately for traffic accidents.
Progressives who applauded the Supreme Court's decision with regard to imposing the death penalty might not be so happy when conservatives turn around and use that decision to justify imposing more parental consent laws on teenage women who are seeking an abortion. And will statutory rape laws need to be revised in light of the findings with regard to the immaturity of teenage brains? Furthermore, if teenagers aren't responsible for their actions with regard to violence, driving, or sex, how can they be expected to cast their ballots responsibly in elections? For that matter, how can teenagers responsibly sign up for military service? And surely the immaturity defense can be used by the tens of thousands of juveniles who are arrested each year for drug abuse offenses.
But let's set aside teenage brains for the moment. What about the brains of adults? A new study from Australia has found that parts of the frontal lobes of drug addicts are underdeveloped. "We believe that this braking system is faulty in patients with compulsive behaviours like addiction, such that affected individuals cannot stop themselves even though they know the consequences of their actions could be devastating," says Murat Yucel, who led the research.
Violent adult criminals also seem to have brain abnormalities that might fall under the Supreme Court's teen murderer decision. Brain researchers at the University of Southern California (USC) imaged the brains of 21 men with psychopathic personalities who had committed serious violent crimes. They found that they had "an 11 percent to 14 percent reduction in the volume of nerve cells in the prefrontal cortex compared to normal males—a deficit of about two teaspoons' worth." Tellingly, Adrian Raine, the USC psychopathologist who headed up the study, noted that the prefrontal cortex appears to be critical for self-restraint and deliberate foresight. "One thing we know about antisocials is that they do not think ahead," said Raine.
So the question naturally arises: If teenage culpability for criminal behavior (and other behaviors, for that matter) is reduced on the grounds that their brains do not function like normal adult brains, shouldn't the culpability of adults whose prefrontal cortexes are similarly underdeveloped be reduced? Should adults with stunted frontal lobes "be expected to transcend their own psychological or biological capacities?"
In any case, what would it mean to "transcend" one's psychological or biological capacities? We're all limited by our psychological and biological capacities. As neuroscience advances and we become better able to peer inside our skulls, we may find that many of us—possibly most of us—have exculpatory neuronal glitches. If a person hits someone else, wouldn't that mean, by definition, that the executive faculties in his frontal lobes had failed to exercise their inhibitory functions? His neurons made him do it; but they are his neurons, and he's responsible for them.
University of California–San Diego neurophilosopher Patricia Churchland points out that a child learns about proper moral behavior in the social world the same way he or she learns about the physical world—that is, by interacting with it himself or watching others. The child then either bears the consequences of his actions or sees the consequences of other people's choices. Churchland concludes, "The default presumption that agents are responsible for their actions is empirically necessary to an agent's learning, both emotionally and cognitively, how to evaluate the consequences of certain events and the price of taking risks."
The Supreme Court's underage execution decision has us slipping far down the slope of universal neurological exculpation, and it raises interesting questions about what standard we should use to hold people responsible in criminal cases. I would suggest an old-fashioned one: If a person can distinguish between right and wrong, then we hold her responsible for her actions. Interestingly, the AMA's amicus brief noted, "Cognitive experts have shown that the difference between teenage and adult behavior is not a function of the adolescent's inability to distinguish right from wrong."
The legal system is part of the social machinery aimed at training our neurons to behave properly. Neuroscience may inform our judgments about whether our neurons have been properly trained, but in the end we have no choice but to hold people responsible for their actions. After all, it's not as though the young murderer in the case the Supreme Court considered got off scot-free. He's likely to be imprisoned for the rest of his life. In this case, one hopes that both teenagers and the rest of us learn impulse control by watching bad things happen to those who don't succeed in controlling their impulses.