Jack P. Shonkoff, M.D.'s  picture
Jack P. Shonkoff, M.D.
Julius B. Richmond FAMRI Professor of Child Health and Development
Harvard School of Public Health and Harvard Graduate School of Education
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The Good, the Bad, and the Tolerable

How Different Stress Levels Impact the Developing Brain

Originally published in Usable Knowledge, a web site of the Harvard Graduate School of Education.

When faced with a potentially threatening situation, like the first day at a new school, a child needs to find a way to cope. But all stress is not created equal. Research shows that excessive experience with toxic stress can disrupt the development of brain circuits related to stress response — and to learning and memory. The National Scientific Council on the Developing Child, headed by HGSE professor Jack Shonkoff, has reviewed what we know about the impact of stress on the developing brain. This article highlights key messages from the Council’s 2005 report, Excessive Stress Disrputs the Architecture of the Developing Brain.

Stress is part of our every-day lives. Our bodies respond to it by releasing chemicals and activating brain circuits that promote adaptive behavior. Stressful events can be harmful, tolerable, or even positive, depending on how much of a bodily stress reponse they provoke and how long the response lasts. To read more about the different types of stress from the Council’s report, click here.

Stress gets under your skin

Dealing with stress involves inter-related brain circuits and hormonal systems. When we are faced with a threat, stress hormones are produced tht send chemical signals throughout the body, including the brain. One hormonal system produces adrenaline under normal circumstances and helps prepare the body for coping with short-term but intense stressors. Another system produces cortisol in response to many forms of stress, also helping to mobilize the body’s energy. Cortisol also has longer-term effects on neural circuits involved in emotion and memory.

Stress-related brain circuits are affected by experience

The brain is very malleable during the early years, so early experiences can have a profound effect on its structure. This “plasticity” means that early experiences shape how readily brain circuits are activated in response to stress, and how well they can be contained and turned off. Toxic stress early in life can lead to poorly controlled stress-response systems.

Young children who are neglected or maltreated have abnormal patterns of cortisol production. Also, a family’s experience of economic hardship is associated with elevated cortisol levels among children. A mother’s depression during her child’s early years can lead to even higher cortisol levels. Under such conditions, the child becomes more vulnerable to a range of stress-related disorders affecting both mental health (e.g., depression anxiety disorders, alcoholism, drug abuse) and physical health (e.g., cardiovascular disease, diabetes, stroke).

Supportive relationships can help compensate for early stress

Fortunately, the plasticity of the brain during the early years can also compensate for some effects of exposure to early stress. In young animals, positive experiences — such as rich opportunities for exploration and social play — are beneficial after prenatal stress and postnatal neglect.

What about stress hormones in children? The body’s response to stressful experience is dynamic. For example, entering a new child care program may initially be stressful to the child, triggering elevations in cortisol. But as the child adapts to the classroom, these routine separations from parents no longer increase production of this stress hormone. Toddlers who have secure relationships with adults have a more controlled stress hormone reaction: when they are upset or frightened, they deal with the challenge without producing elevated levels of these hormones. In contrast, those with insecure or disorganized relationships produce chronically higher stress hormone levels when they are even mildly frightened.

Closing the science-policy gap

Analyzing the nature and severity of early stressful experiences help us make better judgments about potential interventions that reduce the risk of troubling developmental outcomes. Policy implications also arise from our knowledge that sensitive caregiving can serve as a powerful buffer against a compromised stress-response system. To read more about the Council’s policy recommendations, click here.

The complete report, Excessive Stress Disrupts the Architecture of the Developing Brain (Working Paper No. 3), is available via the National Scientific Council’s Web site, http://www.developingchild.net/pubs/wp.html.