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Experts Describe Long-Term Impacts of Stress on the Young Brain


Early exposure to violence and stress not only can affect children's mental and social development during their formative years, it also can increase the risk of alcoholism, illicit drug use, adult depression, anxiety and even heart disease much later in life, according to a leading specialist on stress and resilience.

Judy Cameron, a professor of psychiatry at the University of Pittsburgh, spoke at a 10 July Capitol Hill briefing on "Violence, Stress and Child Development" organized by AAAS through the support of the Dana Foundation and in conjunction with Rep. Chaka Fattah (D-Pa.).

The possible long-term impacts of high levels of stress in early life are emerging in large-scale correlational studies, and the biological mechanisms that may be at work are being studied in animal models such as mice, rats and macaque monkeys.

Cameron and Dr. Felton Earls, research professor of human behavior and development at the Harvard School of Public Health, discussed the impact of violence and stress on the young from differing but complementary perspectives.

Earls and his colleagues have looked at the geographical concentration of violence in Chicago neighborhoods, the factors linked to high homicide rates, and how social cohesion — or what he calls "collective efficacy" — can produce safer neighborhoods and healthier children.


Judy Cameron, University of Pittsburgh [AAAS/Earl Lane]

Cameron has studied how the stress of growing up in unsettled, sometimes violent circumstances affects the development of young brains and increases the risk for destructive behavior and long-term health problems in adult life. Cameron and Earls emphasized that early intervention, both at the community and the personal levels, can make an important difference in a child's life prospects.

Earls noted a striking finding when he and his colleagues correlated a map of 5,000 homicides in Chicago from 1990 to 1996 with a corresponding map of the incidence of low-birth weight babies. "The spatial correlation between the two maps was the same," Earls said.

Cameron said low birth weight is but one of the stressors that can influence how the young brain develops and how a child develops as a person. "The stresses are cumulative over time," she said. Constant exposure to stresses such as poverty, neglect, physical abuse or parental depression, can have a more significant impact on brain development than a transient exposure. The timing of the stress also plays a role, since different areas of the brain develop at different rates. Areas that control hearing and vision develop rapidly, Cameron said, while those involved with complex reasoning and planning don't fully develop until about age 25.

The billions of neurons in the brain already are present at birth, Cameron said, and they begin making connections and forming circuits as the child starts to experience the world. "As a child becomes older, the connections become more efficient," she said, and those that are not used regularly fade away in a process that neuroscientists call pruning. There are actually more neural connections in a child's brain at the age of three than at age 14, Cameron said.

Childhood experiences, both good and bad, can affect the developing architecture of the brain. When parents and other caregivers read frequently to a child, it reinforces the brain connections that will help the child develop reading and thinking skills. Experiences and environment also determine whether neural circuits involved with motor skills, behavior control, memory and other functions form robustly. Experiences also can influence gene expression in the developing brain by affecting the production of proteins that bind to DNA in the neurons, Cameron said. Scientists are just starting to understand such "epigenetic" factors in brain development.

When the body's response to stress — the rush of adrenaline, the increase in heart rate, the elevation of certain hormone levels — is constantly active, Cameron said, the result is "toxic stress" that can reduce the number of neural connections in the cognitive areas of the brain at a time when they should be proliferating.

A Kaiser Permanente study on adverse childhood experiences with 17,000 participants found that childhood exposure to violence, domestic abuse, family neglect or other stresses can have life-long consequences, including a higher probability of alcoholism, illicit drug use and depression. Cameron said the research suggests that children exposed to many adverse events early in life even have an elevated risk of heart disease in their 50s.

There are ways to prevent such outcomes. Good parenting, better nutrition and more cognitively stimulating experiences can "contribute very positively to a healthy trajectory" in life, Cameron said.

Earls led an ambitious longitudinal study in the 1990s to assess the risk factors associated with an epidemic of homicides in Chicago neighborhoods and, just as importantly, to determine what steps could break the cycle of violence. Their work included an analysis of 343 Chicago neighborhoods and the social interactions that influenced the crime rate in those communities.

Communities were being described by race and class, Earls said, but his team wanted to know how they functioned: Are children exposed to good supervision? Would neighbors intervene if they saw children skipping school or spray-painting graffiti on a wall? Or showing disrespect to an adult?

The most important influence on a neighborhood's crime rate, the researchers found, was the neighbors' sense of "agency" or willingness to intervene on behalf of the common good. Based on detailed interviews with 8,782 residents representing each of the 343 neighborhoods in the study, the researchers were able to assign a "collective efficacy" value for each neighborhood. That combined measure of informal social control, cohesion and trust proved to be a robust predictor of lower violence rates in a neighborhood.


Dr. Felton Earls, Harvard School of Public Health [AAAS/Earl Lane]

Earls and his colleagues found that some neighborhoods were functioning well and that the entire city was not under siege as some news reports might suggest. "We found that collective efficacy was, indeed, operating as a protective factor," he said.

The researchers also found that the benefits of collective efficacy go beyond easing violence. It also seems to be associated with more use of parks and recreational spaces in neighborhoods, initiation of sexual activity at later ages among youths, and even less obesity and fewer admissions to hospitals for asthma attacks. While such findings are based on correlations rather than cause-and-effect, the study does suggest that the general welfare of a neighborhood improves when people have a greater sense of social control.

In a follow-up to the collective efficacy study, which was published in Science in 1997, Earls and his colleagues also found that exposure to gun violence about doubles the odds that an adolescent will commit serious violent acts within two years after exposure to gun violence.

At the same time Earls and his colleagues were gathering large amounts of data on Chicago neighborhoods, they also worked with small groups of young people to help better understand what was going on in those neighborhoods. "This process turned out to be very engaging," Earls said. "It gave us a very different sense of teenagers. Rather than being the problem, they were trying to teach us solutions to the problem." This effort, called Young Citizens — Chicago, became an "extremely important component" of the overall research project, Earls said.

During the past decade, Earls has been applying some of the lessons from the Chicago project in another locale and context. He has been measuring collective efficacy at the neighborhood level in the Moshi municipality of Tanzania, a community that has been struggling with high rates of sexually transmitted diseases such as HIV/AIDS. He established a Young Citizens project in Moshi as well, where he is studying the effectiveness of using young adolescents as health agents to promote better education and public engagement on the topic of HIV/AIDS. The results so far have been very positive, he said.

Whether in Chicago or Moshi, "The outcome is a shift from negative thinking to engaging young people in solving problems of violence and sexually transmitted diseases in their environment," Earls said. "When given an opportunity which is structured and self-guided and responsible and dignifies and respects children, there is a tremendous opportunity to curb the bad influences and produce more positive outcomes."