The Violent Brain

Violent behavior never erupts from a single cause. Rather it appears to result from a complex web of related factors, some genetic and others environmental

On September 13, 2006, Kimveer Gill walked into the cafeteria at Dawson College in Montreal and, without apparent motive, shot 21 people, injuring 19 and killing two, including himself. The same day a judge in West ¿Virginia sent a woman to jail for, among other atrocities, forcing her six children and stepchildren to gorge themselves on food and then eat their own vomit. Also on the 13th, a court in New York sentenced a man for killing his girlfriend by setting her on fire--in front of her 10-year-old son. There was nothing special about that Wednesday. From around the world we hear reports of murder, manslaughter, cruelty and abuse every day. Violence is ubiquitous. But what drives one person to kill, maim or abuse another, sometimes for little or no obvious reason--and why do so many violent offenders return to crime after serving time in prison? Are these individuals incapable of any other behavior? We have evaluated the results of studies conducted around the world, focusing on acts ranging from fistfights to murder, in search of the psychobiological roots of violence. Our key conclusion is simple: violent behavior never erupts from a single cause. Rather it results from a combination of risk factors--among them inherited tendencies, a traumatic childhood and other negative experiences--that interact and aggravate one another. This realization has a silver lining: positive influences may be able to offset some of those factors that promote violence, possibly offering hope for prevention.

Impulse Control In 1972 an international team of psychologists launched one of the largest longitudinal studies ever conducted. The Dunedin Multidisciplinary Health and Development Study has now followed approximately 1,000 people born in the New Zealand city of Dunedin for nearly 34 years. Terrie E. Moffitt and Avshalom Caspi, both at King's College London and the University of Wisconsin-Madison, have participated in the study, examining, among other things, antisocial behavior associated with physical violence. They have observed that those who exhibit antisocial behavior fall into two distinct groups. Most are between the ages of 13 and 15, and their delinquency stops just as quickly as it starts. A small minority, however, display antisocial behavior in childhood--in some cases as early as age five--and this conduct continues into adulthood. Among this latter group, almost all are boys.

Perpetrators who carefully plan their crimes typically express no empathy or regret. Indeed, male gender is the most important risk factor for violent behavior. As criminal statistics show, boys and young men commit the majority of physical assaults. According to the Federal Bureau of Investigation's statistics on crime in the U.S., 90.1 percent of murderers apprehended in 2004 were male and men accounted for 82.1 percent of the total number arrested for violent crimes. Girls and women are not necessarily less aggressive, as was assumed until the 1990s. But women engage in more indirect, covert aggression, whereas men tend toward immediate, outward physical aggression. The causes of these gender differences are manifold. Learned sex roles certainly enter into it: "girls don't hit," for example, but "boys need to be able to defend themselves." Also, indirect aggressive strategies require a relatively high level of social intelligence, which girls develop earlier and faster. Moreover, neurophysiological discrepancies almost certainly play a role. The small group of males who exhibit chronic violent behavior from an early age typically share other telltale traits, among them a low tolerance for frustration, ¿deficiencies in learning social rules, attention problems, a decreased capacity for empathy, low intelligence and, most characteristic, extreme ¿impulsiveness. Similarly, repeat offenders--particularly those who have long prison records--seem unable to keep their aggressive urges in check. The late neu¿roscientist Ernest S. Barratt and his colleagues at the University of Texas Medical Branch interviewed imprisoned criminals in Texas in 1999 and found that many inmates consistently picked fights, even though they knew that their lives would be made more difficult as a result. When asked why they continued to behave in ways that hurt them, many responded that they had no idea. Even though they understood the consequences and resolved to act with greater self-control the next time, they did not trust their own ability to keep their impulses at bay.

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