The Neurobiology of Stress: The Human Brain Likes to Be in Balance
Posted Nov 14 2011 10:05am
(Editor’s note: below you have part 5 of the 6-part The Neurobiology of Stress series. If you are joining the series now, you can read the previous part Here .)
Understanding the Human Brain and How It Responds to Stress
The Human Brain Likes to Be in Balance
Fortunately, the brain has some built — in safety systems. Too much cortisol in the blood signals the brain and adrenal glands to decrease cortisol production. And under normal conditions, when the stress is overcome or brought under control (by fighting, fleeing, or turning into an immobile statue, or by mastering the threat), the hypothalamus starts sending out the orders to stand down. Stop producing cortisol! Event over! Under continuous stress, however, this feedback system breaks down. The hypothalamus keeps reading the stress as a threat, furtively sending messages to the pituitary gland, which screams out to the adrenal glands to keep pumping out cortisol, which at this point begins to be neurotoxic — poison to the brain.
Bruce Perry and Ronnie Pollard, a well — respected psychiatrist — neurologist team, have contributed much to our understanding of the impact of stress and how it affects this sense of balance, or homeostasis, in the brain. Sometimes when stress is so intense, the delicate interaction among the brain systems designed to handle it are thrown off balance. Other researchers have also shown that intense, acute, or traumatic stress presents such a shock to the brain and the stress response system that it actually reorganizes the way the brain responds to stress. For example, neuroendocrinologist Bruce McEwen and neuroscientist Frances Champagne have shown that repeated activation of the stress response can result in physical changes, caused by too many inflammatory proteins being pumped into the bloodstream. The research of Michael Meany, a neurobiologist at McGill University, shows that adverse early childhood events (traumas) can actually change the chemistry of DNA in the brain. By a process known as methylation, little chemical markers attach themselves to the genes that control the stress hormone receptors. This makes it hard for the brain to regulate its response to stress.
Let me explain it this way: It’s rather like the keys of a piano being hit so hard that the impact puts the strings out of tune. The piano still plays, but it plays differently. While another hard hit on the keys might have broken a tuned piano wire, the now — slack wire can withstand another hit … and another. If the hits are even harder, the wire stretches more. You can almost hear the piano (and the brain under acute stress) saying, “Go on, hit me again! I can take it.” But the cost is that both are out of tune and the melody is never quite the same. In the human nervous system, this kind of adjustment or adaptation protects the brain from harm by changing the way it responds to stress. Perry and Pollard point out that repeated exposure to stress — chronic stress — results in a new way of coping with a continuous stressor, but it is less effective. Not a good thing.
Both repeated traumas and chronic stress can result in a number of biological reactions. Neurochemical systems are affected that can cause a cascade of changes in attention, impulse control, sleep, and fine motor control. Other researchers have zeroed in on specific parts of the brain that are affected by stress, and their work shows us just how refined and complex this process is. For example, Walker, Toufexis, and Davis suggest that an area of the brain called the bed nucleus of the stria terminalis plays a role in certain types of anxiety and stress responses. Although this area is not thought to be involved in acute traumatic events, these authors have shown that it is responsible for processing the slower — onset, longer — lasting responses that frequently accompany sustained threats. (Aha!) These authors further posit that the physiological reactions in this area may persist even after the threat goes away. (Ah — HA!! ) Why is this relevant? Even when teachers and other professionals try to get these kids to move forward, the memory of past traumatic events lingers on — and impedes efforts to lead students to a higher level of competence.
All of this research has incredible significance in the discussion of kids who are under stress as a consequence of their LD and ADHD. It also has implications for students with other disorders, such as Asperger syndrome and autism. Pollard and Perry tell us that chronic activation of certain parts of the brain involved in the fear response, such as the hypothalamic — pituitary — adrenal (HPA) axis, can wear out other parts of the brain such as the hippocampus, which is involved in cognition and memory. Again, cognition and memory: two of the most important building blocks for successful learning, attention, and social communication.
What ’ s Bullying Got to Do with It?
The underlying thesis of this book is that chronic stress changes brain chemistry and therefore brain function. This connection is made even stronger by a burgeoning amount of provocative new research that sheds light on the adverse impact of bullying on the brains of victims. Dr. Martin Teicher, a neuroscientist at McLean Hospital, a Harvard teaching hospital, scanned the brains of young adults who reported that they had been bullied by peers when they were younger. The brain cells in their corpus callosum, that fibrous bundle of tissue that connects the two hemispheres of the brain, showed evidence of cellular changes that were not seen in a comparable group of students who had not been bullied. The neurons in this part of the brains of victims had less myelin, that is, less of the protective coating that covers the nerves. Since myelin facilitates communication between cells, reduced myelin results in a slowdown in the transmission of brain signals. Rapid and efficient transmittal of neurological impulses in the brain is a prerequisite for effective learning and memory.
Here ’ s the reason this is so important to the discussion of stress: because of the differences that many children with LD and ADHD exhibit (impulsive behavior, poor receptive and expressive language, poor social perception, and so on), they are more likely than other children to be victims of bullying. This is borne out both by research and by clinical observation.
What is clear is that a slowdown in neural transmission in the still — developing brains of young people affects learning, memory, and emotional reactivity. Dr. Tracy Vaillancourt, a psychologist at the University of Ottawa, and her colleagues found that both occasional and frequent bullying can recalibrate the amount of the stress hormone cortisol produced by a group of twelve — year — old victims. Interestingly, she also found that boys who had been bullied had very high levels of cortisol, while corresponding levels were abnormally low in girls who had been harassed. The exact reasons are yet unclear, but we do know that the amount of cortisol is reset or recalibrated in people and animals that are in a state of chronic stress. If girls are neurobiologically more vulnerable to stress, this might account for the difference. Dr. Vaillancourt points out that high levels of cortisol can damage and even kill neurons in the hippocampus. The impact of stress damage can be seen in the results of formal testing. Dr. Vaillancourt found that bullied teens performed more poorly than their peers on tests of verbal memory. She concludes, “Bullying likely diminishes a person’s ability to cope with stress, possibly placing them at risk for psychopathology and ill health.”
And here’s another interesting piece of information generated by Martin Teicher’s work that relates to Dr. Vaillancourt’s. While Teicher did not determine a cause — and — effect relationship, he found that students who had been verbally or physically harassed reported more psychiatric symptoms, including depression and anxiety, than their bully — free classmates.
While additional research is necessary, it is impossible to avoid wondering whether the disability — bullying — stress connection is a significant factor in the lives of many of the children you and I care for and care about.
To Be Continued…
Monday, November 21st: To Fight, Flee or Freeze –That is the Question
– Jerome J. Schultz, Ph.D., the Author of Nowhere to Hide: Why Kids with ADHD and LD Hate School and What We Can Do About It (Jossey-Bass; August 2011), is a clinical neuropsychologist and is on the faculty of Harvard Medical School in the Department of Psychiatry. He served until recently as the Co-Director of the Center for Child and Adolescent Development, CCAD, a multi-disciplinary diagnostic and treatment clinic which is a service of the Cambridge Health Alliance, a Harvard Teaching Hospital.