Toxic Stress: Implications for Policy & Practice

An Interview with Developmental Psychologist Megan R. Gunnar

Abstract: A growing body of science shows the critical effects of an extreme and sustained stressful environment for children on their developing brain architecture and the expression of genes in later life. Toxic stress can shift the brain into surviving in a way that’s more rigid and less adaptive. For example, as a result of biologically altered brain processing, children who have suffered physical abuse may be predisposed to imagine anger in otherwise ambiguous faces. The implications of the science for public-policy decisions are far-reaching. Science reinforces the urgent need to focus on early childhood development, and not to shortchange it, thinking we can compensate later.

Council Member Megan R. Gunnar is the Distinguished McKnight University Professor in the Institute of Child Development at the University of Minnesota. Her research focuses on the emotional and social processes that regulate physiological responses to stressful events early in childhood. She serves on numerous editorial boards, and sits on the advisory board to the Director of the National Institute of Mental Health as well as ZERO TO THREE: The National Center for Infants, Toddlers, and Families. In addition, she was a member of the Committee on Integrating the Science of Early Childhood Development for the Institute of Medicine and the National Research Council of the National Academy of Sciences, and is the recipient of a National Institute of Mental Health Research Scientist Career Award. She earned a Ph.D. in developmental psychology from Stanford University.

What does “brain architecture” mean and how does it work?

Brain architecture, to me, is the basis for everything we’re talking about in connection with the National Scientific Council on the Developing Child. The developing brain organizes itself through the interaction of genes responding to the local environment, and it’s influenced by many things from the outside. So the architecture is about far more than just the “wiring,” or how our brain forms its synaptic connections. It’s about nerve myelination (formation of the fatty insulation around the brain’s nerve cells that ­promotes speedy transfer of signals). It’s about chemical receptors. It’s about how finely tuned we are to receiving different kinds of information and stimulation.

Let’s remember: The process by which the brain builds itself is tangible, it’s physical. And that’s appropriate, since virtually every human function—all our thoughts, all our feelings—has to operate through this physical thing called our brain.

How does stress affect the developing brain and its architecture?

To begin with, the relationship between stress and the brain is a function of both nature and nurture. All of this is a dance between genes and experience. The genes we are born with can be thought of as our “genetic library.” The experiences we have influence which books in that library we take out and read at different points in brain development, and this intertwining of genes and experience determines how the brain develops. Scientists are just beginning to understand how particular genes in our library affect how we react to stress early in life, and what affect this has on how our brains develop and respond to stress later. We know that some children are much more adversely affected by stress than are others and we strongly suspect that this is partly due to the genes they have in their genetic libraries.

Are there critical or sensitive periods during which stress can be especially damaging to the brain?

We’re not quite sure we know the answer to that question. The animal literature strongly suggests there are sensitive periods—stages of development when the brain is particularly vulnerable to toxic stress. We know very little about what’s happening in humans, although we strongly suspect that serious or prolonged forms of stress—which can take many forms, ranging from chronic and untreated childhood illness to physical or emotional abuse—will have the greatest impact during periods of rapid development. These sensitive periods include the fetal period (when the basic structures of the brain are being organized); infancy and early childhood (when the brain is doing much of its basic wiring); and adolescence (when changes in sex hormones are shaping and altering the way the brain processes chemical messages).

Think, for example, about a child who is just learning to walk. When she moved from point A to B by crawling, she could get there even if there were bumps in the road. Once she is a good walker, getting from point A to B even over a bumpy road won’t be a problem. But at the transition between crawling and walking, if we think of that as a metaphor for rapid brain development, even small bumps in the road may send her careening off in another direction. There may be something similar at work regarding adaptation to stress in the young child—periods of rapid change when this deflection point is unusually sensitive, and when early development can be more dramatically affected by stressful events. That is, set off course, slowed down, or otherwise altered from its normal, healthy trajectory.

For information about commonly used terms in Council publications, see Definitions.