 |
At the UC Davis Imaging Research Center, a researcher in Berkeley assistant professor Silvia Bunge’s lab explains the brain-scan procedure to a child volunteer. (Samantha Wright, UC Davis) |
This is your brain on adolescence
MRI studies of young people’s brains show why kids often act before they think
| 29 October 2008
BERKELEY — Every parent of a teenager is familiar with the special behavior that puberty seems to induce — mood swings, slammed doors, rash decisions. Parents often blame such erratic temperament on surging adolescent hormones, but it turns out that the brain has something to do with it, too.
Specifically, a teen’s prefrontal cortex — the piece of brain right behind the forehead that is involved in complex decision making — is not capable of the kind of reasoning that allows most grownups to make rational decisions.
Neuroscience research has shown that while teenagers’ feet may be done growing by the end of high school, their brains are not. The prefrontal cortex of a 15-year-old is very different from that of a 30-year-old, both physically and in how it’s used. For many teens, the output of their underdeveloped decision-processing centers may be as mild as choosing a bag of cheese puffs for lunch or a new purple hairdo. But some youngsters take bigger risks — such as stealing a car or trying drugs. More 17-year-olds commit crimes than any other age group, according to recent studies by psychiatrists.
Silvia Bunge, an assistant professor of psychology at Berkeley, wants to use what she knows about the teenage brain to help society deal with young risk-takers. She is part of the new Law and Neuroscience Project, a MacArthur Foundation group of lawyers and neurobiologists working to incorporate neurology data into the legal system. Bunge feels that current legal attitudes toward teen criminals need revamping.
“Do you put someone away for life who lost his temper at 13, or do you acknowledge that his prefrontal cortex has matured since then?” Bunge asks. “The law is slow to change, but it will, over time, incorporate scientific evidence.”
“This is a very fundamental issue with huge social implications,” says psychology professor Robert Knight, who is working with Bunge on the project. The Law and Neuroscience Project, headquartered at UC Santa Barbara, includes scientists and legal experts from more than two dozen universities in the United States and Canada. Former Supreme Court Justice Sandra Day O’Connor is the honorary chair of the group, and psychology professor Michael Gazzaniga of UC Santa Barbara is the co-director.
The brain’s decision maker
The prefrontal cortex houses many of our difficult decisions. A driver taking the same route to work every day won’t need his prefrontal cortex as he remembers to turn right on Main Street. But if a child darts into the road in front of the car, that part of the driver’s brain switches on as he quickly decides how to react.
Brain-scan and behavioral studies have revealed much about the prefrontal cortex. People with injuries in some parts of it have problems making decisions and take more risks than do healthy adults. The prefrontal cortex is important for learning complicated rules and applying them in different situations. For example, someone with a damaged prefrontal cortex may know to answer a phone when it rings, but she might not understand that it’s socially inappropriate to pick up a ringing phone at someone else’s house, Bunge says.
Strangely, patients with some kinds of prefrontal-cortex damage know right from wrong without being able to act on that knowledge. “The parts of the brain that are important for storing rules are not the same as those that are important for using them,” Bunge says. The prefrontal cortex is also involved in holding our impulses in check. “If you want to fly off the handle and yell at your boss, your prefrontal cortex comes online to remind you of the consequences of your actions,” Bunge says.
Many of these abilities develop as we grow — for example, small children aren’t able to refrain from yelling when they feel angry, but at some point they learn to hold their emotions in check, when appropriate. Bunge’s group currently is testing a training program based on brain research to help children who are behind in school to catch up. She says she’s very excited that her preliminary research with elementary-school children indicates that training aimed at the prefrontal cortex works. Children who played a certain game every day after school for six weeks improved their scores on reasoning tests. “We’re not only training their ability to tackle novel problems, but to control their impulses and ignore irrelevant information as well,” Bunge says. She hopes this research will eventually translate into a training program that could be used for rehabilitation in juvenile-detention centers.
Bunge and Knight are particularly interested in intervention for children from low socioeconomic backgrounds who are more likely than the average teenager to commit crimes and may have less adult guidance and education. The researchers want to help these youngsters learn to make better decisions early — before they get in trouble with the law.
“We want to understand not just the influences that affect criminal responsibility,” says Knight, “but we want to get in earlier in the food chain to examine exactly what the effects of socioeconomic status are in brain development. Do they make you more or less likely to get in trouble with the law? And can we intervene at an early age and improve those skills?”
Scene from a scan
The magnetic resonance imaging (MRI) machine that Bunge’s group uses for brain scans is housed in a special trailer on the Berkeley campus. The machine is shaped like a giant white doughnut, with a small cot in the center for the subject. The MRI uses a very strong magnet to visualize hydrogen molecules in the body. Different tissues show different magnetic signals, so the machine can be used to precisely map the inside of the body — in this case, the brain.
Researchers in Bunge’s lab are conducting scans of children ages 6 to 18 for a novel study on how children’s brains develop. Unlike previous studies that only scanned each subject once and then compared children of different ages, this study will track children as they age by performing two scans, a few years apart, on each child. The scientists take structural MRI images of the kids’ brains to show physical change over time and functional MRIs that measure blood flow in their brains while the children answer test questions inside the machine. Just as blood pumps to flexing muscles, the areas of the brain working hardest are the richest with blood, Bunge says.
During a recent scan, Bunge’s lab manager sat at a bank of large computer monitors in front of a window that looks in on the MRI room. The only visible parts of Mica, the 16-year-old boy in the MRI scanner, were his calves and the red-and-black soles of his basketball sneakers poking out of the machine. Before sending him into the machine, the researcher placed a plastic helmet on Mica’s head. A mirror on top of the helmet allowed Mica to view images projected from the computer screen.
One question in a series designed to test Mica’s reasoning showed a pair of pictures, one of a cat and mouse, the other of a zebra next to a question mark. Below were four choices — lion, giraffe, monkey, or horse. (Mica correctly picked the lion, because lions hunt zebras like cats hunt mice.)
Growing brains
It will be a few years before Bunge knows the full results of this particular study — her research group is still running the youngsters’ first scans and recruiting more volunteers. But through other studies, Bunge has seen interesting changes as brains mature.
In one study, her team found that while adults’ prefrontal cortexes are highly activated in certain areas when they resist impulses, children’s are not. In the real world, this lack of a strong impulse-control center means that teens are less able to withstand the temptation of a new reward, even if it comes with certain risks. “If your friend says, ‘Hey, let’s try this drug, it will be fun,’ you might not be able to use the information you know about the possible negative consequences to resist,” Bunge says.
In a different study, Bunge and her colleagues found that children tend to make riskier choices than adults, and they do so because it’s enjoyable. When faced with different hypothetical choices in the study, adults tended to pick the safe choice, while children often picked the riskier one. The kids knew they were making the risky choice, Bunge says. The study identified a region of the prefrontal cortex that was active as children took the gamble.
From cortex to courts
Contrary to what is often portrayed on popular TV law dramas, the melding of brain images and the law is a new and gray area, says Professor of Law Kathryn Abrams, a participant in the Law and Neuroscience Project. “Right now we don’t know how different kinds of neuroscience are going to have implications for the law,” Abrams says.
“Legal-decision makers will be able to function better if they understand how these differences emerge,” Abrams says. One of the project’s goals is to inform the legal community about the current state of neuroscience research so that lawyers, judges, and juries will better know how to evaluate colorful pictures of brains when they are presented in court.
Insights into how the brain works have already greatly influenced the law as it relates to children. In the 2005 case of Roper v. Simmons, the U.S. Supreme Court ruled that capital punishment for minors is unconstitutional, reversing the death sentence for Christopher Simmons, who killed a woman when he was 17. Groups of scientists sent in “friend of the court” briefs outlining the current state of psychology and neurology research, demonstrating, in part, that the brain does not finish developing until our early 20s.
Bunge hopes her research and that of her colleagues showing that teenagers’ brains make them more prone to poor choices will influence court decisions when kids break the law. ”Overturning the death sentence for minors was a monumental victory,” Bunge says. “But now we need to go one step further and reconsider the large number of teenagers who are in jail for life without parole, and whether or not something could have been done differently with them.”