The science of violence: As the toll of teen violence grows, scientists search for reasons why. (Life Science: Teen Health * The Brain * Hormones).

A 17-year-old is shot and killed after an argument with a group of teens. A 16-year-old gang member slays a police officer. These two violent tales made headlines in America's heartland, Chicago, a steamy week last July. But they could--and have--happened anywhere in the U.S.

Teen violence has especially grabbed the spotlight since 18-year-old Eric Harris and 17-year-old Dylan Klebold launched an assault inside Columbine High School in Littleton, Colo., on April 20, 1999. They shot and killed 13 people and injured more than 20 before taking their own lives--the worst incident of school gun violence in U.S. history.

Since 1994, the number of teens arrested for serious violent crimes--murder, robbery, and rape--has plummeted from more than 500 arrests per 100,000 teens in 1994 to fewer than 350 arrests per 100,000 in 1999. Still, more than 100,000 teens under 18 were arrested for violent crimes in i999, and teen violence in schools has actually increased.

Now scientists are searching for the roots of violent behavior. You'll read some findings on the following pages. But first read each statement below and decide whether it's true or false. Then turn the page to learn more about youth violence.

QUIZ: MYTHS AND FACTS

1. Scientists think some people are born violent--they inherit a "violence" gene.

True False Maybe

2. Exposure to violence in the media (TV, movies, video games, music lyrics, the Internet) causes people to become violent in real life.

True False Maybe

3. Drug and alcohol use is linked with violence.

True False Maybe

4. Children who experience physical abuse are more likely to become violent themselves.

True False Maybe

5. Hormones, puberty, and other developmental factors increase teen violence.

True False Maybe

Answers

1. False. "There is no gene that is a `violence' gene," says Delbert Elliott, director of the Center for the Study and Prevention of Violence at the University of Colorado in Boulder. But that doesn't mean genes (hereditary material in cells) don't play any role in violent behavior. Says Elliott: Scientists just don't yet understand that role.

For example, research suggests people may inherit certain broad personality traits, like impulsivity, the tendency to act or react immediately without mental reflection. A genetic trait like impulsivity combined with environmental risk factors--exposure to street violence or peer pressure from gangs, for example--might increase the chance of someone becoming violent. "But violent behavior is the result of a combination of factors, not any one alone," Elliott says.

2. True. Before American teens turn 18, they've witnessed an estimated 200,000 acts of violence on TV. Evidence suggests exposure to violence in the media can trigger short-term aggressive behavior--behavior intended to harm others, including shoving and starting fights. That aggression usually lasts a few hours or days. Evidence that exposure to media violence causes aggressive teens to rob or murder is far weaker, claims "Youth Violence: A Report of the Surgeon General," published earlier this year.

However, many experts think media violence does exert a lasting impact. Leonard Eron, senior scientist at the University of Michigan's Institute for Social Research, has tracked 856 people since they were 8 years old. He gathered data about their aggression levels as rated by their peers, and the amount and types of TV programs they watched when they were 8, 10, 19, and 30: "We found evidence at each stage that the more violence they watched as children, the more aggressive they were." This includes using abusive language and developing antisocial attitudes.

What about exposure to violence in music lyrics, video games, and on the Internet? Some researchers think violent video games actually teach aggressive behavior because players participate in the violence--think of any game that asks players to "kill" human-looking targets, for example. But far more research on media-linked violence is needed before conclusions can be drawn.

3. True. "Those people who are violent often use drugs, and those people who use drugs are often violent," says Elliott. In a study of 7- to 15-year-old offenders who committed serious violent crimes in Denver, Colorado, about 58 percent regularly used alcohol and 34 percent regularly used marijuana--rates higher than those of non-violent youth. But, cautions Elliott, substance abuse itself doesn't cause violent behavior. In most cases, he says, people already exhibit violent behavior before they ever touch drugs: "The factors in one's background and personality that lead to violence--like impulsivity and antisocial attitudes--are the same things that lead to drug use."

4. Maybe.

Researches disagree on the issue of physical abuse as a violence-causing factor. Physically abused children can suffer from depression and other serious mental health problems, says Elliott. But they're only slightly more likely to become violent than their non-abused peers. "Exposure to violence at home can produce two outcomes," he says. "It can produce an outcome of, `Ah, that's an effective way of getting something I want and I'll use that.' Or else: `I remember what that was like and I'm never going to do that to someone else.'"

Does another form of abuse-bullying--increase the chances someone will become violent? A U.S. Secret Service study of 41 school shooters concluded that bullying played a factor in many crimes: About two thirds of the shooters said they were threatened or attacked by other kids. But psychologist Susan Limber, who studies bullying, stresses that most bullied people--about 17 percent of all students, according to a recent study--never become violent. "Lots of bullied kids are passive kids and suffer silently," says Limber.

5. True. "Developmental factors [like hormones and brain growth] play a role in violence," says Alex Crosby, a medical epidemiologist at the U.S. Centers for Disease Control's Division of Violence Prevention. More than half of all violent youths first become violent in mid- to late adolescence. Violent behavior typically peaks during the late teens, then drops off sharply in early adulthood.

Some research links various hormones--chemicals that affect body functions--to aggressive behavior. Extremely aggressive young children, for example, may produce low levels of cortisol, a hormone secreted during periods of fear and stress. The low hormone level could make some kids more fearless, leading to aggressive behavior, say University of Chicago researchers. But what causes the hormone deficiency, they don't know.

During puberty, hormones influence the functioning of critical brain regions. Also, researchers scanning adolescent brains have discovered some areas don't mature completely until early adulthood. The prefrontal cortex--the brain's "emergency brake," or center for judgment and self-control--is one such area. "Until the judgment and reasoning centers are fully mature, behavior may be more driven by instinct and immediate gratification," says Dr. Jay Giedd, a psychiatrist at the National Institute of Mental Health in Bethesda, Maryland. This may help explain why teens are more risk-prone--including engaging in violent behavior--than adults.

University of Southern California researchers discovered that the prefrontal cortex showed below-normal activity in 42 murderers. Other researchers found a link between low levels of serotonin--a neurotransmitter--and aggression or lack of emotional control. Neurotransmitters are chemicals that relay messages between the brain's nerve cells.

Any theory that explains why teens become violent is only part of a complex picture, scientists say. The vast majority of teens never commit violent acts or crimes. Some risk factors for violence may exist in one's surroundings--involvement with gangs or delinquent peers--rather than in family relationships or hormones. Again, no one factor predicts violent behavior. It's the combination of numerous risk factors that becomes lethal.

The Violent Brain?

Color-coded brain-imaging technology like the PET scan uses harmless radioactive chemicals to track abnormalities in the brain which could be linked to violent behavior.

Some studies suggest that child abuse and neglect can "rewire" developing brains in ways that increase the risk of violent behavior.

One study reports that the prefrontal cortex--the brain region that keeps emotions such as aggression in check--showed below-normal activity in 42 murderers.

A deficiency in three brain chemicals--dopamine, noradrenaline, and serotonin--B has been linked to aggression.

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RELATED ARTICLE: The Neurobiology of Relationships

BY DR. BRUCE PERRY 

THIS IS THE FIRST OF SIX ARTICLES BY DR. BRUCE PERRY ON "CORE STRENGTHS" THAT CAN HELP PREVENT TEEN VIOLENCE. DR. PERRY IS THE PROVINCIAL MEDICAL DIRECTOR OF CHILDREN'S MENTAL HEALTH IN ALBERTA, CANADA. WATCH FOR HIS ARTICLES IN THE NEXT FIVE ISSUES OF SCIENCE WORLD.

Humans are built for love. And the machinery to form and maintain emotional relationships lies in the brain. If someone breaks your heart, the pain is caused by neurons, a network of nerve cells in the brain's limbic system--not your heart. When you form a strong emotional connection or attachment to someone, it's possible because the relationship-mediating systems in your brain are in good working order. And attachment is one reason why most people never become violent.

The neural systems involved in emotional relationships are interconnected to brain systems that mediate pleasure. When someone we're attracted to smiles at us, we feel good. This feature of the brain--getting pleasure from other people--helps create a healthy society.

We are born completely dependent. This means someone has to sacrifice energy, time, and comfort in order for us to survive and thrive. The currency for this human transaction is love. The bond between a loving mother and child provides the reward to keep her going. In turn, the mother's behaviors--rocking, smiling, singing, touching--are transformed by a baby's sensory apparatus into neural activity, which helps the "emotion" systems in an infant's brain develop normally.

When a child doesn't receive consistent loving attention, he or she develops an impaired capacity for emotional relationships. In extreme cases of early emotional neglect, children can grow up with little capacity to relate to and understand others--or empathize. This puts the child at risk for a host of problems, including the capacity to hurt others without any feeling of remorse.

FACTOID: In studies of violent offenders, more than 80% have abnormalities in attachment capacity--in contrast to approximately 12% in the general population.

Did You Know?

* Homicide is the second-leading cause of death for American youths 15-24 years old--accidents are the leading cause of death. Homicide is the leading cause of death for African-Americans 15-24 years old.

* Of the 103,900 youths under 18 arrested for serious crimes in 1999, 1,400 were arrested for murder and 69,600 for aggravated assault, according to the National Center for Juvenile Justice.

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Directions: Write a short essay to answer the following questions:

1. Do you think violent images on TV or violent music lyrics contribute to teen violence? Why or why not? Use specific TV shows or recording artists to support your point of view.

2. In "The Neurobiology of Relationships" Dr. Bruce Perry discusses empathy. What is empathy and how do you develop the ability to empathize with other people?

Cross-Curricular Connection

Social Studies: Research the evolution of TV programming, and give examples of how TV shows have become more graphically violent. Assess how TV reflects society's changing values.

National Science Education Standards 

Grades 5-8: regulation and behavior * personal health * risks and benefits * structure and function in living systems

Grades 9-12: the behavior of organisms * the cell * personal and community health * natural and human-induced hazards

Resources

Youth Violence: A Report of the Surgeon General, U.S. Dept. of Health and Human Services, January 2001 www.surgeongeneral.gov/library/youthviolence/ CDC: Facts About Youth Violence www.cdc.gov/od/oc/medialpressrel/fs2k1017.htm Center for the Study and Prevention of Violence www.colorado.edu/cspv