Monday, August 19, 2013
People are constantly exposed to stressful situations. These may be physical (like participating in marathons, being exposed to radiation, and, perhaps surprisingly, exposed to sedatives or anesthetics). But stress can also be mental, wherein we become anxious and worried over certain events, existing or anticipated. Whether physical or mental, stress activates a brain network involving most directly the hypothalamus, the pituitary gland, and the adrenal cortex to release stress hormones. Such hormones include several cortisone-like compounds called glucocorticoids, and the most prominent one in humans is cortisol.
Glucocorticoids have profound effects on both body and brain. Regulation of glucocorticoids is accomplished by the brain, and learning experiences have profound effects on this control system. Most of what was initially known about glucocorticoids was their effect on the body. I had the great thrill of visiting the pioneer in this field, Hans Selye, in his laboratory complex at the University of Montreal. He had a whole room full of medals, awards, and honorary doctorate diplomas. He won practically every research accolade there was, except the Nobel Prize, one of several grievous slights by the Nobel committee. Dr. Selye wrote an autobiography for my book, Discovery Processes in Modern Biology.
Selye’s research led him to formulate the widely accepted concept of the glucocorticoid system as accounting for a “General Adaptation Syndrome,” which basically explained how the brain and body respond to stress. He discovered that glucocorticoids are “Goldilocks” compounds. That is, a little doesn’t do much, a lot is damaging, and intermediate levels are “just right.”
A moderate amount of cortisol is what is normally released every morning before you awaken. By the way, this is the reason surgeons want to operate early in the morning. This release helps prepare the body for the day’s activities by mobilizing blood glucose, typically by breaking down fat and, if needed, protein stores. Glucose is especially important for the brain, which has huge demands for energy, and which can only burn glucose for energy. Neurons are energized and memory ability is enhanced. Another useful thing cortisol does is to reduce the release of cellular chemicals that cause inflammation.
However, the hormone also inhibits systems that channel resources for growth and reproduction, impairs bone formation, and inhibits the immune system. Basically, the idea is that glucocorticoids help brain and body to respond to temporary emergencies by assigning lower priority to other physiological needs.
The rub comes when stress is prolonged. Selye discovered that the beneficial adaptation to temporary stress cannot be sustained in chronic stress. The system becomes exhausted and control breaks down. Under chronic stress, body muscle mass decreases because the system has been breaking down proteins in order to generate energy. Inflammation bathes cells in toxic chemicals. Infections increase because the immune system has been compromised. In obese people, glucocorticoid levels cumulatively increase in fat cells, increase fat deposits still further, and increase the likelihood of type 2 diabetes and cardiovascular disease.
In the case of brain, persistent high levels of glucocorticoid often causes depression. Memory ability is impaired. Brain degeneration and cognitive decline accelerate. Many neurons are actually killed. What I want to stress here is that chronic high levels of cortisone change the neural circuitry that regulates its release. In other words, the brain learns a new way of functioning if constantly bathed in high levels of cortisone.
Few people make the connection between glucocorticoid control and learning. The neuronal circuits that control hormone secretion learn from stressful experience, just as all neurons learn from whatever they experience. What neurons in the cortisol control circuit learn in chronic stress is that the usual controls can’t work any more.
A typical response to a repeated stress of a certain type (for example, constant quarrels with a spouse or repeated job failures) can be habituation. It’s like “tuning out.” Repeated exposure to the same stress teaches the neurons to stop responding as much as usual. Thus, there is less of the benefits that glucocorticoids provide.
At the same time, the hormone control system becomes hypersensitive to other stresses, especially unpredictable or especially severe stresses. The control system learns to over-react to everything other than the stress to which it has habituated. Now, the damaging effect of too much glucocorticoid becomes pervasive, both for body and brain.
Whether the brain learns stress-coping strategies depends on conscious over-ride of hyper-active responses to stress, because the neural system (the limbic system) that operates our emotions also regulates the glucocorticoid control system. We can not only reduce excessive glucocorticoid but also teach our brain better ways to deal with stress by doing the following:
· Simplify and organize our life,
· Do one thing at a time and finish it,
· Find pleasure in the little things,
· Learn to have a more positive attitude,
· Laugh and be happy,
· Suppress anxiety,
· Be more rational and less emotional,
· Develop supportive social relations,
· Reduce exposure to stressors.
For more on learning and memory in general, see Dr. Klemm’s new book, Memory Power 101, Skyhorsepublishing.com.
Photos courtesy of FreeDigitalPhotos.net, by Artur 84 and Ambro
 Herman, James P. 2013. Neural control of chronic stress adaptation. Frontiers in Behavioral Neuroscience. August 8. Doi: 10.3389/fnbeh.2013.00061