Nov 7, 2011The Neurobiology of Stress: The Stress Response Explained
Stress was put on the map, so to speak, by a Hungarian — born Canadian endocrinologist named Hans Hugo Bruno Selye (ZEL — yeh) in 1950, when he presented his research on rats at the annual convention of the American Psychological Association. To explain the impact of stress, Selye proposed something he called the General Adaptation Syndrome (GAS), which he said had three components. According to Selye, when an organism experiences some novel or threatening stimulus it responds with an alarm reaction. This is followed by what Selye referred to as the recovery or resistance stage, a period of time during which the brain repairs itself and stores the energy it will need to deal with the next stressful event.What is critical to the impact of stress on kids with LD or ADHD is the third stage of the GAS proposed by Selye. He said that if the stress — causing events continue, neurological exhaustion sets in. This phenomenon came to be referred to popularly as burnout. It’s a state of mind characterized by a loss of motivation or drive and a feeling that you are no longer effective in your work. When this mental exhaustion sets in, a person feels emotionally flat, becomes cynical, and may display a lack of responsiveness to the needs of others. Does this sound like any kids with LD or ADHD that you know?What’s going on behind the scenes to cause this exhaustion? When humans are confronted by physical or mental stress or injury, an incredibly complex and critically important phenomenon rapidly takes place. First to be put on alert is the hypothalamus, which is situated deep inside the brain, under the thalamus and just above the brain stem. It’s only about the size of an almond, but plays a crucial role in linking the nervous system to the endocrine system. The hypothalamus is particularly interesting because it controls the production of hormones that affect how the body deals with stress. When danger looms, the hypothalamus sends a nearly instantaneous chemical message down the spinal cord to the adrenal glands, which are located just above the kidneys. This first message signals the production of a stress hormone called adrenaline, also called epinephrine, which is released into the blood stream. Norepinephrine also plays a role here. The interaction of these two hormones controls the amount of glucose (sugar) in the blood, speeds up the heart rate, and increases metabolism and blood pressure, all of which get the body ready to respond to the stressor.Meanwhile, the hypothalamus has been closely monitoring these changes, as well as the source of the stress, and now releases something called a corticotrophin — releasing hormone (CRH). CRH travels along the neurons that go from the hypothalamus into the pituitary gland. This important gland, which is located at the base of the brain just above the roof of the mouth, releases something called adrenocorticotropic hormone (ACTH) into the bloodstream. ACTH travels down to the adrenal glands. This triggers the adrenal glands to release another hormone called cortisol. (Seriously, folks, isn’t this just amazing? )Some cortisol (it’s a steroid, by the way — you’ve probably used cortis one cream to quell some itch) is present in the bloodstream all the time. Normally, it’s present at higher levels in the morning and much lower at night. Incidentally, recent research has found that the opposite is true in some children with autism, a finding that might shed light on this condition. A little cortisol is a good thing. It can give you that quick burst of energy that comes in handy for survival purposes. For a brief period, it can enhance your memory and help boost your immune system. The right amount of cortisol helps keep your body systems in a healthy balance, and it can fight against inflammation and even lower your sensitivity to pain — all good things when you’ve been injured or if you’re going into battle against a single stressful opponent. But as often happens, too much of a good thing is, well … you know.The stress response described here temporarily turns down or modifies nonessential bodily functions and activates the ones we need to keep us safe and healthy. It’s a wonderfully efficient system, and it’s fine — tuned to do its job well. Our brains and bodies are exquisitely designed to handle occasional acute stresses or injuries. However, they’re not well — equipped to handle ongoing or chronic stress.Hans Selye’s research on the impact of stress in rats formed the foundation on which most subsequent studies about stress were built. Over time, and with the aid of sophisticated brain imagining technology, Selye’s hypothesis has been scrutinized and expanded. He believed that all types of stress resulted in the same reaction in the brain, but we now know that this process is much more complex. For example, contemporary research shows that the brain responds in different ways based on its perceptions of the degree of control that a person has over a stressful event. Here’s how this plays out in the brain.The more stress people are under, or think they are under, the greater the amount of cortisol that’s pumped into the blood by the adrenal glands. If too much cortisol is produced (as in acute stress) or is maintained at high levels in the bloodstream for too long (as in chronic stress), it can be very harmful. This hormone can cause a variety of physical problems, including blood sugar imbalances like hypoglycemia (a disturbance in the functioning of the thyroid), a decrease in muscle tissue and bone density, and high blood pressure. It can also make the body susceptible to disease by lowering immunity and inflammatory responses in the body and making it harder for wounds to heal. Prolonged exposure to excessive amounts of cortisol has been implicated in the rise of obesity because too much cortisol has been shown to be related to an increase in the amount of abdominal fat.
Being overweight can lead to a host of other problems, including a decrease in “good” cholesterol (HDL) and an elevation of “bad” cholesterol (LDL) as well as metabolic disorders, heart attacks, and strokes. Most important to our discussion of stress in the lives of students with LD and ADHD is that too much cortisol can cause brain changes that result in impaired cognitive performance.