Consider the brain in violence studies Lack of serotonin could be responsible for some behavior

March 16, 1997|By Norbert Myslinski

IN ONE DAY this month in Baltimore, five people were murdered in five separate incidents. That raised the city's murder rate to 53, compared with 45 at the same time last year. Despite all our efforts, violence continues to escalate.

Poverty, drugs, guns and dysfunctional families all have been blamed for violent behavior. In one publication, researchers listed 15 theories on the origins of violence. However, none of them referred to a critical element. Not one made any reference to the brain.

Despite the fact that all behavior is rooted in the anatomy and biochemistry of the brain, the vast majority of research into violent behavior concerns itself with cultural and societal causes, very little with the neurological causes.

Scientists have long known that brain damage can increase impulsive behavior. Just as damage to the brain can result in loss of motor control or loss of sensory function, it also can result in loss of emotional control.

The brain damage can occur during early development or later in life. Two of the best predictors of violent behavior are childhood head injuries or neurological deficits such as epilepsy or learning disabilities. In one study of 286 people exhibiting impulsive violent behavior, 94 percent had neurological deficits detectable by tests such as EEG or CT scans.

The damage also can be acquired later in life from trauma, tumors, stroke, brain infections or certain diseases. Any form of brain damage, if it occurs in key areas of the brain, can lead to recurrent violent behavior in previously peaceful individuals.

One such key area is the amygdala, which is located in the temporal lobes or sides of the brain. Electrical stimulation of the amygdala in animals or humans leads to spontaneous and uncontrollable rage, which stops as soon as the electrical current stops. Removal of the amygdala produces the opposite effect: excessive submission without fear.

Up to half of all patients with temporal lobe epilepsy suffer sudden outbursts of aggression and violence. Vincent van Gogh was a victim of this disorder, which led him to cut off his left earlobe with a razor.

These examples demonstrate that certain parts of the brain are responsible for inhibiting impulsive violent behavior. Other studies have shown that certain brain chemicals play the same role.

One such chemical is serotonin. Research over the past two decades has demonstrated an association between low brain serotonin and violent behavior. This is one of the most consistently replicated findings in behavioral biochemistry.

One of the first to demonstrate this relationship was Dr. M. Asberg, who studied depressed patients. He observed that those patients with the lowest levels of serotonin were the most likely to attempt suicidal violence.

Three years later, G.L. Grown found the same relationship between serotonin levels and externally directed violent behavior. He used a lifetime aggression score based on the actual incidence of overly aggressive behaviors.

Using the Psychopathic Deviance Scale of the Minnesota Multiphasic Inventory, Brown also was able to demonstrate that the low serotonin syndrome was a long-term trait of the individual rather than a temporary state of brain chemistry. The conclusion was supported by a later study that found low serotonin levels in young adults correlated with a childhood history of aggressive behavior such as the impulsive killing of pets, setting fires, stealing and lying.

Serotonin is an intrinsic part of the brain's impulse control system. If we lose it, we lose control. This is consistent with what know about the organization of the brain. The frontal cerebral cortex, which has its greatest development in humans, inhibits our basic violent tendencies. Normally, serotonin is released in the frontal cortex, where it interacts with a protein known as the serotonin receptor to produce inhibition. While this control is active and healthy in most of us, it is lacking in some who commit violent crimes.

Neuroscientist Rene Hen developed an exceptionally ferocious rodent, which he calls the "outlaw mouse," by deleting the gene for the serotonin receptor. And a study of violent Finnish criminals showed an association between altered serotonin levels and a possible flaw in a gene responsible for the synthesis or serotonin.

The violent behavior associated with serotonin is impulsive, unpremeditated and occurring with minimal provocation. There is no economic motivation for the violence and the victim usually is unknown to the offender.

Unfortunately, this is only one type of violence that plagues our society. Most neuroscientists who study violent behavior candidly admit that their work offers no cure for the majority of violence. Some chronically violent people, however, may suffer a structural or chemical imbalance in their brains. This is important because it is one of the causes of unpremeditated homicide, suicide and the abuse of spouses, children and animals.

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