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This article is from the In-Depth Report How Can Science Help Make Sense of the Arizona Massacre?

What Causes Someone to Act on Violent Impulses and Commit Murder?

Some people are able to control anger or frustration and channel these feelings to nondestructive outlets. Others, like the gunman accused of killing six people during the assassination attempt on Rep. Gabrielle Giffords, exhibit a frightening lack of control
psychiatry, assassination



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People are often confronted with feelings of disappointment, frustration and anger as they interact with government officials, co-workers, family and even fellow commuters. Most can control their actions to the extent that relatively few of these interactions end in violence. The attempted assassination of U.S. Rep. Gabrielle Giffords (D–Ariz.) last weekend shows, however, sometimes the cognitive control mechanisms required to guide one's behavior are either nonexistent or ignored, with disastrous consequences.

Giffords and several others were fired on at close range Saturday during a public gathering for her constituency outside a Tucson, Ariz., supermarket in the representative's home district. Before the shooter could be wrestled to the ground and disarmed six people were dead and 14 wounded, including Giffords who was shot in the head. The accused gunman, 22-year-old Jared Lee Loughner, apparently expressed contempt for the government on a number of issues via MySpace rants and YouTube videos. He allegedly took his grievances with the government and society in general a step further in November when he bought a 9-millimeter Glock 19 handgun and began planning to assassinate Giffords.

The criminal justice system will have to determine the specific motives and mental competency of Loughner, but Scientific American interviewed Marco Iacoboni, a University of California, Los Angeles, professor of psychiatry and biobehavioral sciences and director of the school's Transcranial Magnetic Stimulation Laboratory, about why some individuals act on their violent thoughts whereas others do not. Iacoboni is best known for his work studying mirror neurons, a small circuit of cells in the brain that may be an important element of social cognition.

[An edited transcript of the interview follows.]

What turns anger into action?
Mostly cognitive control, or to use a less technical term, self-control. About a year ago I was in Davos at the World Economic Forum, and we had a dinner-with-talks on intelligence. University of Michigan professor of social psychology Richard Nisbett, the world's greatest authority on intelligence, plainly said that he'd rather have his son being high in self-control than intelligence. Self-control is key to a well-functioning life, because our brain makes us easily [susceptible] to all sorts of influences. Watching a movie showing violent acts predisposes us to act violently. Even just listening to violent rhetoric makes us more inclined to be violent. Ironically, the same mirror neurons that make us empathic make us also very vulnerable to all sorts influences.

This is why control mechanisms are so important. Indeed, after many years of studies on mirror neurons and their functioning we are shifting our lab research to the study of the control mechanisms in the brain for mirror neurons. If you think about it, there must be control mechanisms for mirror neurons. Mirror neurons are cells that fire when I grab a cup of coffee (to give you an example) as well as when I see you grabbing a cup of coffee. So, how come I don't imitate you all the time? The idea is that there are systems in the brain that help us by imitating only "internally"—they dampen the activity of mirror neurons when we simply watch, so that we can still have the sort of "inner imitation" that allows us to empathize with others, without any overt imitation.

The key issue is the balance of power between these control mechanisms that we call top-down—because they are all like executives that control from the top down to the employees—and bottom-up mechanisms, in the opposite direction, like mirror neurons. Whereby perception—watching somebody making an action—influences decisions—making the same action ourselves.

What has neuroscience uncovered about the capacity of the person who shot Giffords, the person responsible for the Virginia Tech massacre in 2007, and many others (yet still a small percentage of people) to behave so violently?
What happens in these individuals is that their cognitive control mechanisms are deranged. Mind you, these individuals are not out-of-control, enraged people. They just use their cognitive control mechanisms in the service of a disturbed goal. There are probably a multitude of factors at play here. The subject is exposed to influences that lead him or her to violent acts—including, unfortunately, not only the violent political rhetoric but also the media coverage of similar acts, as we are doing here. A variety of issues, especially mental health problems that lead to social isolation, lead the subject to a mental state that alters his or her ability to exercise cognitive control in a healthy manner. The cognitive control capacities of the subject get somewhat redirected—we don't quite understand how—toward goals and activities that are violent in a very specific way. Not the violent outburst of somebody who has "lost it" in a bar, punching people right and left. The violence is channeled in a very specific plan, with a very specific target—generally fed by the media through some sort of rhetoric, political or otherwise—with very specific tools, in the Giffords case, a 9-millimeter Glock.

What are the signs that a person is disturbed enough to take action?
The signs are quite visible, although difficult to interpret without a context—and unfortunately they unfold very quickly, and people can rarely witness them before the action is taken. The action itself is a sign, a desperate form of communication from a disturbed individual. Unfortunately, nobody was chatting with the guy when he left his final messages on Internet before getting into action. But I bet that if somebody was communicating with him before the act and saw those signs and read those messages on MySpace or whichever social network he was using, that person could have done something, could have engaged him in a sort of conversation that might have redirected his deranged plans. Indeed, by connecting with the subject, that person might have redirected some of the activity of mirror neurons toward a truly empathic behavior, rather than in the service of the deranged imitative violence leading to action.

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