December 10, 2004

The Long-term Impact of Stress During Childhood on Brain Development

Researchers are starting to understand the long-term impact that early childhood stress (either short term, high stress or ongoing moderate stress) has on the brain.

Losing a parent or witnessing domestic violence as a young child is a devastating experience that can leave long-lasting emotional scars. Scientists are beginning to understand how such events can affect memory and behavior into adulthood, and how well-timed interventions can help.

Two new studies -- one with humans, another in animals -- demonstrate the profound effects of early trauma. Preschoolers living in a stressful home had weaker memories when they reached middle school. And monkeys who were taken away from their mothers during the first month after birth had long-lasting changes in behavior and responses to stress.

By learning more about how early stress affects the developing brain, scientists hope to figure out ways to help young children when they need it most.

"If we can understand when the brain's most sensitive stages occur, we can tailor interventions to periods with the greatest impact," said Paul Plotsky, a neuroscientist at Emory University in Atlanta.

Stressful experiences, such as taking an exam or visiting the doctor, send a cascade of hormones to the brain and nervous system to mobilize the body's defenses for a threatening situation. But prolonged stress can overload the brain, turning an adaptive response into one that causes harm.

Early stress may be even worse. Researchers think that trauma during childhood can influence the way the brain's stress system develops, making people or animals more vulnerable to illnesses such as anxiety and depression, and to cognitive problems.

In research presented at the Fall, 2004 Society for Neuroscience meeting in San Diego, researchers found that stresses, such as a lack of nurturing in the early years, affected a young child's learning and memory later in life. Children who lived in less-nurturing environments as preschoolers performed worse on memory tests in middle school.

Researchers determined the stress level of a child's home with site visits, noting how warm and affectionate parents were, their approach to discipline and whether they encouraged children by displaying their artwork on the wall. Their scores weren't affected by other factors, such as the mother's IQ, the mother's drug use during pregnancy, or cognitive stimulation, indicated by the number of toys and books they had as toddlers.

Martha Farah, a researcher at the University of Pennsylvania in Pittsburgh who led the project, described the memory and IQ differences as statistically moderate, but said, "I was shocked when I saw how big the difference is."

In a separate study involving primates, researchers found that moderate stress can have long-lasting behavioral effects, but the precise nature of the change depends on when the trauma occurs.

Baby monkeys were taken from their moms at different stages and raised in familiar social groups. Those whose mothers were taken away when the babies were 1 week old became socially withdrawn and reacted poorly under stressful situations as adults. Monkeys who were separated from their mothers at 1 month old became very gregarious and often ate more to deal with sources of stress -- for example, introduction to a new social group.

Many children who have lost a parent respond by becoming quiet and withdrawn, or by constantly seeking attention. The monkeys reacted very similarly to children, said Judy Cameron, a scientist with the University of Pittsburgh in Pennsylvania and Oregon Health & Science University who led the research.

The good news was that these monkeys' behavior changed when they were placed with a surrogate mother early on.

"If we give them to a 'supermom' who loves to nurture babies, they respond rapidly and don't show [social problems] later on," Cameron said.


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