Teens’ brains hold key to their impulsiveness

Partly developed brake
The inexplicable behavior and poor judgments teens are known for almost always happen when teens are feeling high emotion or intense peer pressure, conditions that overwhelm the still-maturing circuitry in the front part of brain, Giedd said.

As Steinberg sees it, a teenager’s brain has a well-developed accelerator but only a partly developed brake.

By around 15 or 16, the parts of the brain that arouse a teen emotionally and make him pay attention to peer pressure and the rewards of action — the gas pedal — are probably all set. But the parts related to controlling impulses, long-term thinking, resistance to peer pressure and planning — the brake, mostly in the frontal lobes — are still developing.

“It’s not like we go from becoming all accelerator to all brake,” Steinberg said. “It’s that we go from being heavy-foot-on-the-accelerator to being better able to manage the whole car.”

Giedd emphasized that scientists can’t yet scan an individual’s brain and draw conclusions about how mature he is, or his degree of responsibility for his actions.

Brain scans do show group differences between adult and teen brains, he said, “but whether or not that should matter (in the courtroom) is the part that needs to be decided more by the judicial system than the neuroscientist.”

Steinberg, who frequently testifies on juvenile justice policy and consults with state legislators on the topic, said it’s not clear to him how much the research on teen brains affects lawmakers. They seem more swayed by pragmatic issues like the cost of treating teens as adults, he said. But he noted that he has been asked to testify more in the past few years than before.

Dividing line of maturity
In any case, experts say, there’s nothing particularly magic about the age 18 as a standard dividing line between juveniles and adults in the courtroom.

Different mental capabilities mature at different rates, Steinberg notes. Teens as young as 15 or 16 can generally balance short-term rewards and possible costs as well as adults, but their ability to consider what might happen later on is still developing, he said.

A dividing line of age 18 is better than 15 and not necessarily superior to 19 or 17, but it appears good enough to be justified scientifically, he said.

Steinberg said he thinks courts should be able to punish some 16- or 17- year olds as adults. That would be reserved for repeat violent offenders who’ve resisted rehabilitation by the juvenile justice system, and who could endanger other youth in the juvenile system if they returned. “I don’t think there are a lot of these kids,” Steinberg said.

For the rest, he thinks it makes sense to try rehabilitating young offenders in the juvenile justice system. That’s better than sending them through the adult system, which can disrupt their development so severely that “they’re never going be able to be a productive member of society,” Steinberg said. “You’re not doing society any favor at all.”

Ash said that to decide whom to treat as an adult, courts need some kind of guideline that combines the defendant’s age with the crime he’s accused of. That should leave room for individual assessments, he said.

But “we don’t have very good measuring sticks” for important traits like how impulsive a juvenile is, he said.

In any case, the decision for each defendant should balance a number of reasons for punishment, like retribution, protecting society, deterring future crime, and rehabilitation, said Ash, who’s a member of the American Psychiatric Association’s Committee on Judicial Action.

Even if a 14-year-old murderer is held morally responsible for the crime, he will have matured by the time he’s 18, and in the meantime he may be more amenable to rehabilitation than an adult murderer is, Ash said.

In fact, most experts conclude that rehabilitation works better for juveniles than for adult offenders, he said.

And just as parents know how irrational juveniles can be, Ash said, they also know that rehabilitation is a key goal in punishing them.

“What we really want,” he said, “is to turn delinquent kids into good adults.”

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