The New York Times Magazine
October 16, 2004

Too Immature for the Death Penalty?

Just after 2 a.m. on Sept. 9, 1993, Christopher Simmons, 17, and Charles Benjamin, 15, broke into a trailer south of Fenton, Mo., just outside St. Louis. They woke Shirley Ann Crook, a 46-year-old truck driver who was inside, and proceeded to tie her up and cover her eyes and mouth with silver duct tape. They then put her in the back of her minivan, drove her to a railroad bridge and pushed her into the river below, where her body was found the next day. Simmons and Benjamin later confessed to the abduction and murder, which had netted them $6. Police called it "a cheap price for a life."

The two were convicted. Benjamin was sentenced to life in prison, and Simmons was given the death penalty. The Missouri Supreme Court overturned Simmons's sentence last year, and the case is now before the U.S. Supreme Court, which recently heard arguments on the constitutionality of the death penalty for those who are 16 or 17 when they commit their crimes. (The court has already ruled against execution of anyone under 16.)

Unlike other death-penalty cases, this one has drawn intense interest from the American Medical Association, the nation's psychiatrists and psychologists and other health and research groups. They've filed briefs with the court making a novel scientific argument — that juveniles should not be executed because their brains are still developing. In other words, teenagers cannot be held fully responsible for their actions because all the wiring to allow adult decision making isn't completed yet. As Stephen K. Harper, a professor of juvenile justice at the University of Miami School of Law, puts it, "Adolescents are far less culpable than we knew."

The briefs in the Simmons case are based on research that shows that the human brain, once thought to be fully wired by about age 12, continues to grow and mature into the early or mid-20's. And the last part to mature is the frontal lobes, or prefrontal cortex, responsible for all the hallmarks of adult behavior — impulse control, the regulation of emotions and moral reasoning.

"Scientists can now demonstrate that adolescents are immature not only to the observer's naked eye but in the very fibers of their brains," says the brief by the A.M.A. and the psychiatrists. "Normal adolescents cannot be expected to operate with the level of maturity, judgment, risk aversion or impulse control of an adult."

Parents of teenagers might greet this news by asking what, exactly, we are paying our scientists to do. We don't need a neuroscientist to tell us that adolescents sometimes make dumb decisions. That has been clear since the first protohuman teen defied his parents' orders to get back to the cave before dark. The question is: Why do they act that way?

"The old idea was that adolescence was a social phenomenon, not biological," says Dr. Jay Giedd, a psychiatrist and the chief of brain imaging in the child psychiatry branch at the National Institute of Mental Health. Teenage turmoils were thought to be shaped by the instruction we received from parents and peers in the arts of growing up. Giedd was one of the first to provide a visual demonstration that "maybe it's not social, maybe there is actual biology to explain why a lot of cultures have put age limits on things." He made images of children's and teenagers' brains with an M.R.I. scanner, repeating the scans every two years for more than a decade, to see how the brain changed. The images showed that the brain continues to develop until the mid-20's, and it does so in an unexpected way.


The amount of gray matter — made up of brain cells and their connections — increases until the brain has more than it needs. This occurs in different parts of the brain at different ages; in the frontal lobes, the growth continues until about age 11 in girls and 12 1/2 in boys. Then the brain begins to "prune" that excess gray matter, severing some of the connections. At the same time, it reinforces other connections, wrapping them with white matter, a heavier layer of insulation also known as myelin. This pruning and reinforcement represents the maturing of the brain. The process continues into the mid-20's.

All the while, the brain is adapting to its environment. A teenager who studies the piano, for example, will strengthen connections in the auditory part of the brain. Another who studies drawing will do the same in the visual cortex. And all of us who fail to learn a foreign language before our early teenage years will prune the connections we used to learn our own language — and condemn ourselves to years of struggling with French verbs.

Nobody is arguing that teenagers deserve a pass; the new brain science is not a get-out-of-jail-free card. Sometimes adolescents do appear to act like adults — but the point is that they can't do so consistently. And even when they seem to be acting like adults, they are using their brains in a different way. Adolescents, unlike adults, often operate from a more instinctual, reflexive part of the brain.

Abigail Baird, a developmental neuroscientist at Dartmouth, asked teenagers ages 12 to 18 to identify emotions on faces in photographs. She monitored their brains with a functional M.R.I. scanner, which shows which parts are active during a specific task. When adults see faces, the amygdala kicks in to say "this is something important." Then the frontal lobes make an assessment, check with memory and other parts of the brain and coordinate a response. ("It's my wife and she doesn't look happy. Better run out for flowers.") Almost all the time, adults get the emotions right.

When Baird scanned teenagers, however, she found that they often misidentified the emotions in the pictures. When shown a face expressing fear, for example, they would identify it as surprise, or even happiness. "The finding was that the alarm system — the amygdala — was ready to go," she said. "But the interpreter — the prefrontal cortex — doesn't care, and they don't seem to be able to make it care." The amygdala zeroed in on the faces as something important, but the frontal lobes couldn't focus enough to get the identification right.

Teenagers in stressful situations — under the influence of peer pressure or, like Simmons and Benjamin, in the midst of committing a burglary — are not going to act like adults. Their brains can't handle it. Beatriz Luna, a neuroscientist at the University of Pittsburgh, has compared the brains of adults and teenagers doing a task in which they must resist the instinctive tendency to gaze at a dot of light on a computer screen. As in Baird's experiments, adults recruit various parts of the brain to help. But teenagers don't seem to do that. "It takes them an extreme effort," says Luna. "When everything is perfect, they can act like adults. But you add a little bit of stress, and that can break down."

The lesson applies widely. "This is why kids who are good kids, who know right from wrong, sometimes do stupid things," says Dr. David Fassler, a psychiatrist in Burlington, Vt., and a spokesman for the American Psychiatric Association on this issue. "They act on impulse."

How, then, do most teenagers survive adolescence without harming themselves or winding up in jail? Good parenting is one reason, Baird says. "The people around you are like an external frontal cortex," she says.

None of this means that Simmons should be absolved of his repugnant crime on the grounds that his amygdala made him do it. The question is whether he, and others who are 16 or 17 when they commit their crimes, should be held to the same standard as adults. "There's no question that the new science is changing the debate," says Laurence Steinberg, a psychologist at Temple University and the director of the MacArthur Foundation Research Network on Adolescent Development and Juvenile Justice. In 2002, the Supreme Court ruled that mentally retarded criminals are exempt from the death penalty because of "disabilities in areas of reasoning, judgment and control of their impulses." The scientific evidence suggests that 16- and 17-year-olds share similar "disabilities" in reasoning and judgment.

The Missouri attorney general, in his petition to the Supreme Court, argues that the court should not ban the juvenile death penalty until there is a national consensus supporting a ban. A consensus may be forming — seven states, not counting Missouri, have eliminated the juvenile death penalty since 1989, some by getting rid of executions altogether. So has the federal government. But 19 states still allow such executions.

In an interview with The St. Louis Post-Dispatch two years ago, Simmons, then 26, said he broke into Crook's house to get money for drugs. How did that lead to murder? "I ask myself why, and I don't understand why," he said. "We just lost all sense of stealing things."

Was Simmons thinking and acting like an adult when he murdered Shirley Ann Crook? That's a question science can't answer. As the A.M.A. and the psychiatrists write in their brief, scientists can "shed light on certain measurable attributes" related to teenagers' culpability. But "science cannot, of course, gauge moral culpability." That is what the Supreme Court must do.