Early Violence Leaves Its Mark on the Brain

Adolescent violence is traced to abuse and neglect in childhood

Early Violence Found to Be Etched in the Brain

WITH rates of violence among teenagers rising precipitously, the argument over the causes of violent behavior has never been more charged. Nature got a hearing last month at a University of Maryland meeting on possible genetic influences on violence. Last weekend, nurture had its day, at a meeting at the New York Academy of Sciences on the childhood causes of violence.

Several strands of findings presented by researchers at the weekend conference pointed to the same conclusion: brutality and cruelty to children can leave a clear mark on the chemistry of the brain. And those changes in brain chemistry may be the route by which a brutalized child becomes a violent adult. The conference also offered some glimmers of hope for changing an established inclination to violent behavior.

One animal study that was particularly telling showed that normally mild-mannered golden hamsters that were threatened and attacked when they were young, and that grew up to be cowardly bullies, had lasting changes in the brain circuitry for two neurotransmitters that regulate aggression. And parallel data from several long-range studies of large groups of children show that those who were childhood victims of abuse or neglect were the most violent as teenagers.

The hopeful news came from programs that seek to help these children learn to better control their aggressive impulses.

Even if a child has a predisposition to aggression, he can learn to override it, said Dr. Karen Bierman, a psychologist at Pennsylvania State University. The more aggressive kids just need more help from their parents, teachers and friends.

The research on golden hamsters took advantage of that species' habit of living singly, and being fiercely protective of their nesting territory---or, in this case, laboratory cage.

In the wild, adolescent hamsters ordinarily go off on their own and establish a solitary nest. But in the experiment, adolescent hamsters were placed in the cage of a mature one, thus violating its territory, for an hour a day over a week's time---about half a hamster's adolescence. The older hamsters threatened and attacked the younger ones to protect their territory from the interloper.

When those younger hamsters grew up they were given their own territories, and experimenters placed other hamsters in the cages of the traumatized ones. If an interloper was the same size, the traumatized hamster tended to cower or run.

But if the interloper was smaller and weaker, the resident hamster attacked--- with a vengeance. They were far more aggressive than normal, said Dr. Craig Ferris, a neuroscientist in the Behavioral Neuroscience Program in the psychiatry department at the University of Massachusetts Medical Center in Worcester. He conducted the study with Dr. Yvonne Delville.

In a related study, anatomical studies of adult hamsters that had gone through similar experiences showed changes in the neural circuitry for vasopressin, a brain substance involved in the regulation of aggressive impulses in hamsters. The vasopressin circuitry was diminished, with less of the substance being synthesized by the cells. That seems to make the receptors for the scarcer vasopressin more sensitive. Dr. Ferris plans to do similar anatomical studies of the hamsters that were terrorized in adolescence.

For serotonin, which plays a role in restraining aggressive impulses, the traumatized hamsters had circuitry that secreted larger amounts of the neurotransmitter, which seems to make the receptors for serotonin less sensitive. The serotonin system is just not doing its job, Dr. Ferris said.

Exactly how all this affects the hamsters depends on what they are confronting. Normally, vasopressin facilitates aggression and serotonin inhibits it, but the system doesn't work very well in these hamsters, Dr. Ferris said. They either get too timid or you get an explosion of aggression, depending on whether they are with an animal of equal size or one that is a potential victim.

Sluggish serotonin circuitry seems typical of more violent humans, too, according to studies in which people are injected with a dose of fenfluramine, a substance that stimulates receptors for serotonin. The injection leads to the release of prolactin, a stress hormone that can be measured in the blood; higher levels of prolactin indicate greater serotonin activity.

We find that people who are easily angered and impulsive---prone to shouting and throwing things, for example---release less prolactin than those who are not so irritable and impulsive, said Dr. Emil Coccaro, a psychiatrist in the Clinical Neuroscience Unit at the Medical College of Pennsylvania in Philadelphia. That implies that the less active or responsive your serotonin system is, the more impulsive and aggressive you'll be.

Several studies presented at the conference showed that children who were abused or otherwise severely stressed in childhood were far more likely than others to be violent as teenagers or adults. And, again, some of the data implicated changes in serotonin or related neurotransmitter systems.

Dr. Cathy Spatz Widom, a psychologist at the State University of New York in Albany, identified 908 children who had been victims of criminal neglect or physical abuse that led to the filing of criminal charges. Tracking the children's criminal records over the next 20 years, she found that those who had been childhood victims of neglect went on to have 50 percent more arrests for violent crimes than did a comparison group, while for.those who suffered physical abuse, the rate of violent crimes was double that of the comparison group.

Similar findings were reported from a study of 66 aggressive boys winnowed from an overall sample of 1,037 inner-city children in Montreal. While the neighborhoods themselves tend to breed children somewhat more prone to aggression, these 66 boys were at the age 6 already the most violent among them.

These are the boys who are always getting in trouble for fighting all through elementary school, said Dr. Richard Tremblay, a psychologist at the University of Montreal, who reported the main results of a 10-year study that assessed the boys annually. As adolescents, these are the boys most frequently involved in crimes, especially violent ones. And, he said, they come from families that tend to be more physically punitive with their children, beating them or using other physical punishment.

A test of pain sensitivity---an indirect measure of serotonin function---in these same boys suggested that they had lower levels of the substance, according to data presented by Dr. Jean Seguin, a colleague of Dr. Tremblay.

Louise Arseneault, a graduate student at the University of Montreal who worked on the study, presented data showing that the aggressive boys had difficulty focusing on activities and were easily distracted. The result is that they are impulsive, she said, and so unable to inhibit bad behavior---even if they know they'll be punished for it---they don't seem to be able to stop themselves.

Boys who showed this deficiency on neuropsychological tests had the biggest increase from the age of 13 to 14 in picking fights and other aggressive acts---a jump of 50 percent. Their main deficiency, Ms. Arseneault said, is in self-regulation, the ability to keep yourself from fighting because you know it's bad or inappropriate.

At the weekend conference, Dr. Adrian Raine, a psychologist at the University of Southern California, reported on a study of 4,269 boys, some of whom suffered some form of birth complication and whose mothers were abusive or neglectful in infancy. He found that those boys with birth complications and abuse were three times as likely as the others to be arrested for a violent crime by the age of 18.

Particularly damaging, Dr. Raine said, is early child abuse, like shaking a child vigorously. He said, We know that can lead to laceration of the white nerve fibers that link the prefrontal cortex to deeper brain structures like the amygdala, which are involved in the generation of aggressive impulses, while the prefrontal lobes inhibit those impulses.

The ability to control aggression is learned during childhood. The crucial importance of such childhood learning was underscored by studies done with rhesus monkeys in which some monkeys were raised by their mothers, and others spent childhood without their mothers but in the company of same-aged peers. The result of the motherless childhood was something like a rhesus version of Lord of the Flies.

While mother-reared monkeys with low serotonin levels are more aggressive than others as juveniles, they are also more prosocial, engaging in many friendly acts, too, said Dr. Gary Kraemer, a psychologist at the Harlow Primate Laboratory at the University of Wisconsin.

But if they have low levels of serotonin and are raised deprived of interaction with their mom, they show inordinate, unpredictable and extreme aggression, Dr. Kraemer said. The rhesus mother helps the young one learn to organize its responses to other monkeys.

Those results, of course, can be read as hopeful as well---since mothering has such a powerful effect on modifying aggressive impulses. And at the conference, educators presented hopeful reports on special programs lo help more aggressive children learn to keep their impulses under better control.

We see that after a year, children who are prone to aggression can learn to talk about their feelings and think of different ways of solving a difficulty instead of just hitting, said Dr. Karen Bierman, a psychologist at Penn State. But the interventions can't be just with the child---parents and friends have to help the child find alternatives to aggression and learn a broader array of skills for resolving problems.

Dr. Bierman reported results from a curriculum used in the early grades to teach children better ways to manage their emotional impulses. In one technique, for example, teachers help children recognize the cues in their bodies that signal that they are about to lose control and lash out, and remind them to calm down instead. The children also regularly pair up with a buddy to play games, supervised by a trained neighborhood volunteer, and solve problems that commonly lead to fights at that age, for example, learning about the need to take turns.

We think doing this repeatedly and consistently helps children build self-regulation skills for handling aggressive impulses, said Dr. Mark Greenberg, a psychologist at the University of Washington who is a colleague of Dr. Bierman. Presumably, it strengthens connections between the centers for emotional control in the prefrontal lobes and those for emotional impulse in the limbic areas.

Dr. Bierman reported that the program resulted in fewer arguments and fights in the classroom and the playground, and enabled children who were prone to aggression to control their impulses. This, in turn helped them to become more popular with their playmates.

The brain circuits that regulate aggression in humans are malleable through childhood, so there may be some corrective experiences that reverse or otherwise improve any adverse impact from early abuse, Dr. Ferris said. My hope is that we'll focus resources on these kids so they don't go down the path of social failure and inappropriate, excessive aggression.

(Photo Caption)
In stained cross section of brain of a bullied golden hamster, bottom, the vasopressin system, which regulates impulsivity and aggression, is depleted compared with that of the dominant hamster, top. Similar changes persist in adult brains when hamsters are bullied as adolescents.