Amygdala Abnormalities Linked to Violent Aggression
> 11/8/2007 10:53:48 AM

Patients struggling with uncontrolled aggressive urges often appear irrational and frightening to the victims of their impulsive rages as well as anyone who happens to witness them in action. Such behaviors are most commonly seen among teenagers and young adults, and experts have long suspected abnormal brain functions to be at least partly responsible for their seeming inability to restrain themselves. New research focuses this hypothesis on the amygdala, the brain structure most directly responsible for instinctual, reactive behaviors and defensive responses to outside stimuli.

Researchers at the University of California San Diego gathered a control group and a selection of adolescent boys whose overly aggressive behavior had led to disciplinary problems in the past. The teens in this study were not necessarily psychotic or antisocial. They fell under the label "reactively aggressive" - that is to say that they frequently overreacted to perceived offenses and experienced serious problems in controlling their subsequent impulses, often assaulting people or striking inanimate objects in response to what were inevitably revealed to be simple misunderstandings or exaggerated interpretations of benign behavior. Most importantly, all showed remorse for actions that, beyond the heat of the moment, they clearly recognized as inappropriate.

All subjects viewed images of models forming various facial expressions. When confronted with threatening faces, the amygdalas in the problem group lit up with a veritable storm of activity. Their amygdalas seemed to override the better judgement of the reasoning prefrontal cortex, where activity slowed in these moments of distress. If confronted with such threatening figures in real-world situations, these patients may very well have lashed out verbally or physically, and the MRIs show that the unusual relationship between those two sections of the brain is largely responsible for their behaviors. Researchers have previously noted smaller-than-average prefrontal cortices in the brains of murderers and antisocial criminals, displaying the same sense of imbalance that may well lead to their often destructive outbursts. The boys in the study had thankfully not reached such stages yet, but the trends observed in the clinic do not bode well for future behavioral trends. But how do these abnormalities come about? While genetics plays an obvious role, environmental conditioning has also been proposed as a root cause: physical abuse and neglect, as well as early drug and alcohol use, have been shown to alter the brain in potentially profound ways.

One of America's greatest tragedies served to reinforce the role played by the amygdala in regulating deadly aggression (or failing to do so). In August, 1966, 25-year old University of Texas at Austin student, Marine and Eagle Scout Charles Whitman climbed to the top floor of the school's observatory tower and proceeded to shoot 31 people with a high-powered rifle. 14 of those victims died, and after Whitman was killed by police, the bodies of his wife and mother were discovered in their homes. In a note written after the first murders, Whitman noted that he had been experiencing "unusual and irrational thoughts" and ventured to guess that his newfound sense of irrational rage could be explained by some sort of physical abnormality. His autopsy proved him right: Whitman had a walnut-sized tumor on his amygdala. The cancerous growth pressed against the structure, keeping it stimulated at all times and facilitating his deadly, seemingly motiveless rampage.

The most upsetting implications of this study run into territory previously explored in the pages of popular science fiction - medicine may very soon allow experts to identify those at risk of violent behavior and impulse control disorders before they've even started school. If this situation arises, what would make for an appropriate method of response? Should authorities take some sort of action to ensure that these children do not go on to lives of violent crime? What would that decision entail, and how do we draw the line between those who qualify and those who don't? Aggressive behavior is a very basic part of human nature, but most people are able to contain it within reason. Would ignoring the signs of a future problem leave doctors or parents culpable if and when these children act on their unchecked impulses? Researchers believe that the time to consider these potentially controversial issues is now.

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