Stress and the Architecture of the Brain

By Dorian Friedman

Abstract: When faced with threats to physical or psychological well-being, our bodies and brains respond in a variety of self-protective ways, including the production of stress hormones adrenaline and cortisol. Our ability to turn this response on and off is critical to healthy functioning in society, and scientists now believe that significant adversity—and the lack of a supportive environment of relationships—in early childhood can trigger lifelong problems regulating this stress system. A nurturing, supportive environment may be the best protection a child can have against the harmful effects of stress in early life. Studies prove that it’s easier and less expensive for society to provide what’s needed in early childhood than to remediate for the aftereffects later in life. Scientists note four key areas in which policies and scientific knowledge are at greatest variance: starting before birth; confronting child abuse and neglect; ensuring the best possible child care; and addressing depression and other mental-health challenges.

As the latest science reveals discoveries about human development, we are learning important lessons about what it takes to build sturdy architecture in the human brain, and about what can get in the way of its development. We know that the quality of a child’s earliest experiences is critically important. Nurturing relationships are so fundamental, in fact, that the growing brain’s architecture depends heavily on them. (For more on the relationship between caregiver-childhood interaction and the brain, see “Interaction and the Architecture of the Brain”.)

At the same time, science is teaching us valuable lessons about how the brain’s intricate architecture can be weakened or compromised when things go wrong. We now know empirically that exposure to frequent stress causes the release of harmful chemicals in a child’s developing brain that can impair its physical growth and make it harder for neurons to form connections with each other. The weakening of the brain’s architecture, in turn, impacts a child’s ability to respond positively to future stresses, including normal life obstacles. In addition, it can have direct and long-lasting physiological consequences, such as increasing a child’s vulnerability to later problems ranging from anxiety and depression to cardiovascular disease, diabetes and stroke.

What does “stress” mean in this context? Broadly defined by developmental scientists, stress refers to “the set of changes in the body and the brain that are set into motion when there are overwhelming threats to ­physical or psychological well-being.” (From Neurons to Neighborhoods, National Research Council and Institute of Medicine, 2000.) For our purposes, such stress can arise from a wide range of stimuli—from acute fear or mild anxiety, from physical ailments including sickness and hunger, or, most pointedly in children, from interaction with adults who are themselves under stress.

The Brain Responds

Well before birth, the human body choreographs its response to external events with a delicate interplay of hormones and neurochemicals. In the face of a stressful event such as fear or anxiety, receptors in the brain and the adrenal glands shift into high gear to produce two key hormones: adrenaline and cortisol.

Just as the immune system defends the human body, a well-regulated stress-response system is essential to preserve life. Without the so-called “flight/fight” instinct at the heart of our stress response, it seems unlikely that our prehistoric ancestors could have survived to evolve into modern humankind. However, like the immune system, our stress system can threaten our well-being if it is activated too often or without careful calibration. And that, in short, is what happens when a young child experiences stress for too long or too regularly. An excess of these chemicals floods the developing brain with a corroding effect on its architecture. Eventually, stress chemicals begin to damage vital regions—such as the hippocampus and amygdala—areas responsible for learning, memory, and emotional responses, among other critical functions.

It’s useful to think of our stress system as a thermostat, suggests Pat Levitt, director of the Vanderbilt Kennedy Center for Research on Human Development at Vanderbilt University—and this thermostat can be damaged by unusual amounts of stress early in life. Under normal conditions, our bodies tell our brains when to raise the thermostat—producing needed hormones—and when to lower it as the source of stress subsides. “Our ability to turn this response on and off is very important,” he says. Here’s the rub: Early life experiences shape how readily the stress system is activated and how well it can be turned off. And childhood adversity, it turns out, “shapes a stress system that has trouble lowering the temperature, or flipping the ‘off’ switch.”

Learning from Animal Research

Much of what science tells us today about stress and the brain comes from animal experiments. In various studies, researchers tested what would happen to baby rats if their mothers were subjected to stress. When they disrupted the mother’s nest and interfered with her maternal instinct, for example, her “pups” grew into more fearful adults, poorly equipped to handle stress. In related studies, scientists also have shown how stress to rats during pregnancy causes a range of problems for their offspring later in life. Interestingly, though, these outcomes differ based on the care babies received from their mothers: Pups raised by nurturing rat mothers fared well, but those with inattentive mothers showed impaired memory and learning abilities, and were more fearful and reactive to stress. But beyond these behavioral differences, the neglected pups showed physical problems in brain architecture—with fewer nerve connections in important parts of the brain.

Studies of rhesus monkeys have revealed similar patterns. Baby monkeys who are temporarily removed from their mothers develop brains that look different from “normal” monkey’s brains, with structural differences in the amygdala and prefrontal cortex. These differences vary depending on how early the separation occurred. Further study of these differences may lead scientists to important conclusions about how the timing of stressful events may affect brain development. The research also may lead to cures.

And the Human Brain?

Can we apply these important findings about animals to our own children? A growing body of evidence suggests these are important lessons for human development, even though scientists can’t yet say definitively what stress does to specific regions of the human brain.

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