"Teachers: Nikki neuron reminds you to check the standards tables in the front of the toolkit to see which ones apply for this lesson and your subject area."
Recent research has made it clear that stress is an important factor in illness and behavior in general, but it especially plays a critical role in depression. Therefore, we need to understand stress in order to understand depression.
What is Stress?
Stress can be defined as our physical and/or psychological responses to changes that occur around us that place abnormal demands on us. The late Dr. Hans Selye1,2 was the most prominent early researcher and theoretician on stress. Although many more recent researchers have added considerably to the understanding of stress, Selye’s initial work proved to be foundational. He defined many of the terms used in current stress research. Some important concepts he developed include:
■ Stress — the response of a person to any demands that are sufficient to disturb homeostasis; the stress response tries to keep one’s systems in homeostasis.
■ Homeostasis — the state in which all systems in the body are functioning normally and smoothly, and there is no net loss of energy or ability to cope.
■ Stressor — any event that requires us to change or to adapt.
■ Distress — more stress than we can effectively cope with.
■ Eustress — effort without distress, having an effective capacity to cope.
Stress isn’t just determined by what happens to us; it also depends on how we perceive the stress or how we react to it. A football game might be very stressful to one person, while enjoyable to another. The same could be true for a book report; one person might find it a stressful chore, another, an interesting learning experience. A person’s response to stress also depends somewhat on one’s basic personality. A person who is a worrier will experience more stress than someone who is not. While a person may not be able to change his or her basic personality, one can learn, through education or therapy, to moderate or reduce the fight-flight response to stress by practicing stress management skills.
The Fight-Flight Response to Stress
When we encounter changes in our environment or something perceived to be dangerous, frightening, or difficult, our bodies go through many changes to better enable us to adapt to or deal with the stressor. Things that frighten or anger us trigger the fight-flight response, which is an inherited, “built-in” tendency we all have acquired through natural selection to help us deal with emergencies. (More recent research in stress adds a third “f” to the fight/flight response: “freezing,” which sometimes is observed in organisms responding to danger, the opossum being one excellent example.3)
Dozens of things change in our bodies in times of danger (or perceived danger): We breathe faster to get more oxygen into our bodies to fuel our response to the stressor, our heart pumps faster to get the blood quickly to the large muscle groups we will need to use in order to fight or flee, adrenaline rushes into our bloodstream to give us greater energy and strength, our muscles tense up and prepare for strong physical activity, and our pupils dilate to let in more light so that we can see better.
Incoming sensory information is first appraised by the old primal systems of the brain (first the hindbrain, then the midbrain) to determine the threat potential. In other words, the “old brain” reacts in a “fight vs. flight” context, in terms such as, is this a “kill or be killed” situation, should I run away, what must I do for immediate survival? If danger is perceived, then primitive survival instincts are activated, directed by the lower regions of the brain. If no immediate threat exists, the information is evaluated according to more everyday adaptation (e.g. eat when hungry, drink when thirsty). Only if our brain perceives that there is no immediate danger or survival issue do we have the luxury of allowing our higher brain center, the forebrain and cerebral cortex, to take primary responsibility for processing the information.4 Being aware of the brain’s hierarchical mode for handling input from our environment helps us understand why we often don’t think clearly about the consequences of our actions when we are highly emotional.
Is Stress Good or Bad?
When we all lived in caves and faced saber-toothed tigers, an instinct-driven brain made perfect sense; we’d see a tiger, our bodies would kick into fight-flight mode, and we’d have lots of energy and strength to either run from or try to fight off the tiger. Now, in our more civilized world, the fight-flight response doesn’t help us as much; our stressors tend to be things like getting upset at our parents, spouse, boss or friends. It is not always productive or socially appropriate to fight or run from these stressful situations. The unexpended energy is experienced in our bodies as tension.
So, while the stress response is normally a good thing, it becomes a problem when it is chronic, severe or exceeds our natural capacity to cope. With chronic stress, a person stays in a state of hyper-vigilance and heightened arousal. Then stress becomes more than just feeling a little emotionally upset. It can actually cause physical problems, even changes in the brain.5,6 Research has shown that high levels of stress can impair immune system function, making one more vulnerable to infection.7,8 In one well-known study, medical students taking an exam had their blood drawn before and afterwards to measure levels of immune-response cells.9 The post-exam measures were significantly lower, apparently as a result of the stress of taking the exam. This may explain why we sometimes get sick after a period of high stress: Our body’s ability to fight off infection has been compromised by the stress.
On the other hand, too little stress can lead to complacency, a lack of being challenged, or a lack of alertness. You need a reasonable amount of stress to keep you alert and motivated to use your abilities to meet challenges and solve problems. For instance, if you are about to fall asleep, you won’t do very well on a test. If you are excited about the big game, but not too excited, you’ll be motivated to do well and are likely to perform better than if you were bored and uninterested. However, if you get too excited, the level of your body’s arousal turns into anxiety that can actually interfere with your performance.
The relationship between stress and performance10 can be plotted on a graph, with a stress level rating from low to high on the horizontal axis and performance measures from low to high on the vertical axis. The points on the graph, when connected, will form an inverted U-shaped curve (called a Yerkes response curve11). This curve shows how people typically perform under varying amounts of stress: If stress is low, performance improves with an increase in stress. But at very high levels of stress, the effect is reversed, resulting in declining performance. The ideal amount of stress for optimal performance is somewhere in the middle range.
So is stress good or bad? It can be either. Stress helps us accomplish the basic tasks of everyday living, like waking up to alarm clocks and working for our paychecks. The stress response is what helps us to slam on the brakes in time to stop short of the car ahead that has suddenly come to a halt. Even the happy things in our lives can be stressful if they are major events with a strong emotional impact. Your first date, going to the senior prom, a big party, getting married, having a child, getting a job promotion, even going on a big vacation – all are things we look forward to experiencing, but because of their importance, carry the potential for stress. Too much stress, for whatever reason, makes it harder to cope well.
The Caveman and the Lion12
Imagine a caveman out foraging for food in the savanna, and around the next tree he comes face to face with a lion. What does the caveman’s body need to do to survive? Run away fast. His muscles need all the energy they can muster, energy produced by burning glucose. Therefore, the stress response consists of producing glucose out of fat cells, liver cells, etc. for use by the muscles. Cortisol, a hormone from the adrenal gland, accomplishes this. To deliver all the necessary glucose to the muscles, the heart rate and blood pressure need to rise (this is accomplished by adrenaline and noradrenaline), and the need for oxygen increases so respiration also increases. Along with these responses, there are changes in his brain. Because the reticular activating system (RAS) of the brain is pounding away, and blood flow to the brain is boosted, especially to the frontal lobes, the senses become sharper and memory improves. The survival value of these changes to the brain is that they enable one to remember that man cannot outrun a lion; therefore, he needs an escape plan.
There are also a number of energy-consuming processes that the caveman will need to shut down in order to optimize energy use to meet the demands of this emergency: digestion, tissue repair, reproduction, sex drive and fighting infections. Therefore, during the stress response, his body stops tissue repair, curtails the production of hormones related to sperm (or egg) production, and the immune system is suppressed. The pain threshold is increased, so that if the caveman is clawed by the lion, he can still try to escape.
The manifestation of the stress response is normally short lasting and occasional. It is not intended for repeated, long-lasting responses to the environment. If chronic, the stress response can debilitate and even kill just as surely as a lion can, but more slowly. If the stress response is elicited repetitively for prolonged periods, the increases in blood pressure can lead to heart disease, including heart attacks and strokes. The skin does not repair the wear and tear of everyday aging; a simple paper cut can take days to heal or may scar. Poor use of glucose can lead to a form of diabetes; egg production or sperm count drops; libido (sex drive) decreases; and the body’s ability to fight infections, including cancer, is reduced.
One recent animal study points out the difference between acute and chronic stress. When one is first exposed to stress, learning is improved. But after periods of chronic stress, the dendrites in the hippocampus, a part of the brain involved in learning and memory, begin to shrink. This leads to diminished cognitive performance.6,13
The Neurobiology of Stress
A growing body of research indicates that chronic stress, besides increasing the potential for physical ailments, increases one’s vulnerability for development of depression.14,15,16 The causes of depression are not fully understood. However, the most widely accepted theory at present attributes depression to disturbances in normal brain chemistry function, involving certain neurotransmitters, especially serotonin and norepinephrine. Stress, through its influences on the body’s HPA axis, has the potential to negatively influence this brain chemistry. Genetic and environmental factors are also believed to be key, with the level of stress in one’s life playing a prominent role.
Stress, Depression and the HPA Axis Connection 17,18
Stress effects are regulated by the body’s steroid hormone system, the Hypothalamic-Pituitary-Adrenal (HPA) axis, called this because it involves these three bodily organs in a feedback loop. Evidence indicates that chronic stress can lead to a malfunctioning HPA axis feedback loop; that dysfunction seems to be associated with the development of depression. The mood-regulating neurotransmitter serotonin is particularly affected by the performance of the HPA axis.
When the HPA axis works normally, a perception of a stressful event causes the HPA axis to initiate the fight-flight response to prepare the body to deal with the threat:
■ The sympathetic nervous system is aroused and the fight-flight response is triggered, including the release of adrenaline from the adrenal gland.
■ The reticular activating system stimulates the hypothalamus to release the hormone Corticotropin Releasing Factor (CRF) into the bloodstream.
■ The CRF stimulates the pituitary gland to release adrenocorticotrophic hormone (ACTH) into the bloodstream.
■ The ACTH travels to the adrenal glands, located on top of the kidneys, causing the release of cortisol, a longer-acting human stress hormone.
■ The hypothalamus monitors cortisol level in the blood, so when enough cortisol has been released, the hypothalamus adjusts its release of CRF so that the amount of cortisol in the blood stays at a healthy level.
Adrenaline (the neurotransmitter epinephrine) increases your heart rate, affects your blood vessels, and raises your blood pressure. The adrenaline rush one feels during an exciting or dangerous situation is an effect of the increased epinephrine in the brain and cortisol in the bloodstream. Cortisol (glucocorticoid) is a steroid with powerful effects, necessary at moderate levels for a variety of bodily functions. However, high levels of cortisol over time can cause harm.5
When the HPA axis works normally, it initiates the sequence of events described above, with the hypothalamus completing the cycle by regulating cortisol. But for individuals with chronic stress and depression, this feedback mechanism doesn’t work as well. The hypothalamus either fails to recognize abnormally high cortisol or is unable to lower it. It may be that the hypothalamus habituates (becomes accustomed to) elevated cortisol. Whatever the reason, the malfunctioning feedback loop results in a chronically high blood level of cortisol, which in turn can impair the parts of the brain that regulate mood and the capacity to experience pleasure. This may make persons with chronically high stress more likely to become depressed. 6,14,19,20,21
It has been clearly established that stress and depression are linked, but it isn’t clear which causes the other, or if both are a result of some other process. It is, however, well established that stress and depression are related to serotonin and the HPA axis.22 Individuals under chronic stress who also have a family history of depression are especially vulnerable to developing a depressive illness.
Stress Management: Ways to Cope with Stress23,24
There are numerous techniques for dealing with stress, but they all boil down to two options: Change or avoid the source of stress (change the environment) or improve your ability to cope with stress (change yourself).
The first thing to consider is whether you can eliminate or avoid, in some way, the thing that causes you stress. Of course, this is not always possible, but if you can easily avoid or change what is causing the stress without creating other problems or without being too avoidant of life and responsibility in general, then this might be tried first. But if eliminating the source of stress means dropping out of school or having your boss kidnapped, maybe that shouldn’t be your first choice!
If changing or avoiding the source of stress is not a good option, then your alternative is to change yourself and your response to the stress. Learn where you experience stress in your body. Know your “early warning signs” of stress so you can use your stress management skills to “de-stress” early on when interventions are more effective. Some people notice muscle tension in the neck, stomach or hands. Others notice rapid breathing or increased heart rate, while still others may notice a flushed face or sweaty palms. Whatever your early warning signs, learn to recognize them so you will know it is time to manage your stress.
Measure stress in yourself by rating it from 1 to 100 (low to high) and watch it change over time. Rate your stress levels throughout the day to see if you are more likely to experience greater stress at some time rather than another. Try one of the techniques described below then rate your stress level afterwards to see how well it worked. Graph your stress ratings over time. Sometimes, just increasing your awareness of stress helps you to better manage it. (For an example, see the stress rating handout.)
■ Relaxation exercises: Learn to relax muscle groups throughout your body on cue so you can use this skill on a moment’s notice to reduce tension. Practice calming the muscle groups one by one. Focus on one area of the body. Tense the muscles for a few seconds, then relax them. Or do a total-body exercise by tensing then relaxing the entire body at once. Pay close attention to how your muscles feel both when they are tense and when they are relaxed, so that you can become more aware when your body is under stress. As you continue to practice this technique, try to increase the degree of relaxation in the muscles. You might find it helpful to try this with your eyes closed.
■ Breathing exercises: In response to stress, the fight-flight response tends to make us breathe rapidly and shallowly. However, this can lead to hyperventilation and panic, or more often, general distress. Learning to breathe correctly, in a way that mimics what we do when we are calm, can help us to gradually get the flight-flight response under control.
Diaphragmatic breathing exercise (imagine a balloon in your abdomen): The main thing is to breathe 1) slowly, and 2) deeply, from the belly. To slow down your respiratory rate, count while inhaling slowly, then hold your breath for the same count. Finally, exhale for the same count. With each breath, increase the number of seconds you count. This will force you to breathe more slowly. To be sure you are breathing deeply, imagine that each inhalation is blowing up a balloon in your belly. Involving the abdomen in this way will involve your diaphragm more (muscle tissue in your abdomen which helps with efficient breathing) in breathing, which increases the efficiency of your respiration. You should notice your abdomen swelling up as you “inflate the balloon” and become more relaxed in the process.
■ Meditation: There are a variety of ways to meditate (traditional contemplative prayer, quiet contemplation of a repeated thought, Transcendental Meditation, a scientifically based “relaxation response” and others). Scientific research has shown that this type of activity can be very calming and can improve your ability to tolerate stress.27
■ Visual imagery: Take time out from your stressful day to imagine a pleasant and calming scene and place yourself in it. The more details you can build in the scene and the more vivid you can make it, the more real and effective the image will be.
■ Moderate physical exercise: Regular and moderate physical exercise does more than benefit our physical health. Many studies have shown that exercise can be an effective way to improve your emotional and mental health and even help reduce depression in some cases.28
■ Positive self-talk: Calming and positive self-talk can help turn around a stressful situation. Talk to yourself with phrases such as “I am calm, I can stay relaxed,” “Breathe deeply and slowly, let the tension go,” or “I can handle this.” Stress-prone people often do the opposite, frequently thinking in extremely negative ways about the situation or their ability to cope with it. Improve this inner self-talk and you will reduce your perception of stress and thus your stress response.
■ A balanced, healthy lifestyle: Proper nutrition, sleep, and time set aside for recreation, relationships and spiritual growth help maximize your capacity to withstand the physical and psychological effects of stress. Overeating is a common way to cope with stress that may seem to help you feel better at first, but in the long term, can cause more problems than it solves.
■ Avoidance of alcohol and drugs as a way to cope with stress29: Substance abuse only creates its own set of stressors, so avoid relying on drugs or alcohol to relieve stress.
Other Tips for Handling Stress
■ Identify stress in your life.
■ Make a plan for how to deal with the stress.
■ Think of alternatives for handling the situation so you are less likely to feel stressed.
■ Practice stress management techniques to improve your coping ability.
■ Try acting as if you are calm and see if your stress rating changes for the better.
■ Try to see the humor in situations that are stressful but you can’t avoid.
■ Think about how you will perceive this stressful event in five or 10 years so that you gain some perspective on the problem.
The Medical Basis of Stress, Depression, Anxiety, Sleep Problems and Drug Use http://www.teachhealth.com/ (Award-winning website about stress)
1. Selye H. Stress without Distress. New York, NY: Signet; 1975.
2. Selye H. History of the stress concept. In: Goldberger and Breznitz, eds. Handbook of Stress: Theoretical and Clinical Aspects. 2nd ed. New York, NY: The Free Press; 1993.
3. Marks IM. Fears, Phobias, and Rituals: Panic, Anxiety, and their Disorders. New York, NY: Oxford University Press; 1987.
4. Damasio, Antonio. The Feeling of What Happens:
Body and Emotion in the Making of Consciousness. Austin, Texas: Harcourt; 1998.
5. Sapolsky R. Why stress is bad for your brain. Science. 1996;273(5276):749-750.
6. Sapolsky R. Why Zebras Don’t Get Ulcers. New York, NY: W.H. Freeman & Co; 1998.
7. Cohen S, Herbert TB. Health psychology: psychological factors and physical disease from the perspective of human psychoneuroimmunology. Annual Review of Psychology. 1996;47:113-142.
8. Chrousos GP, Gold PW. The concepts of stress and stress system disorders: overview of physical and behavioral homeostasis. JAMA. 1992;267:1244-1252.
9. Malarkey WB, Pearl DK, Demers LM, Kiecolt-Glaser JK, Glaser R. Influence of academic stress and season on 24-hour mean concentrations of ACTH, cortisol, and ß-endorphin. Psychoneuroendocrinology. 1995;20:499-508.
10. Koob GF. Arousal, stress, and inverted U-shaped curves: implications for cognitive function. In: Lister RG, Weingartner HJ, eds. Perspectives on Cognitive Neuroscience. New York, NY: Oxford University Press; 1991.
11. Yerkes RM., Dodson JD. The relation of strength of stimulus to rapidity of habit-formation. Journal of Comparative Neurological Psychology. 1908;18:
12. Garcia-Rill E. Personal communication; 2002.
13. Sapolsky RM. Stress, the Aging Brain, and the Mechanisms of Neuron Death. Cambridge, Mass:
The MIT Press; 1992:3-11.
14. Brown GW, Harris TO, Hepworth C. Life events and endogenous depression: a puzzle reexamined. Archives of General Psychiatry. 1994;51:525-534.
15. Gold PW, Goodwin FK, Chrousos GP. Clinical and biochemical manifestations of depression: relation to the neurobiology of stress. New England Journal of Medicine. 1988;319:413-420.
16. Paykel E. Causal relationships between clinical depression and life events. In: Barrett JE, ed. Stress and Mental Disorder. New York, NY: Raven Press; 1979.
18. Kaplan HC, Sadock BJ, eds. Comprehensive Textbook of Psychiatry, 5th ed. Baltimore, MD: Williams & Wilkins; 1991.
19. Post RM. 1992. Transduction of psychosocial stress into the neurobiology of recurrent affective disorder. American Journal of Psychiatry. 1992;149:999-1010.
20. López JF, Chalmers D, Little KY, Watson SJ. Regulation of 5HT1a receptor, glucocorticoid and mineralocorticoid receptor in rat and human hippocampus: implications for the neurobiology of depression. Biological Psychiatry. 1998;43:547-573.
21. McEwen H. The neurobiology of stress: from serendipity to clinical relevance. Brain Research. 2000; 886(1-2):
25. Charlesworth EA, Nathan RG. Stress Management: A Comprehensive Guide to Wellness. London: Souvenir Press Ltd; 1993.
26. Davis M, McKay M, Eshelman E. The Relaxation and Stress Reduction Workbook, 5th ed. Oakland, CA:New Harbinger Publications Inc; 2002.
27. Bishop SR. What do we really know about mindfulnessbased stress reduction? Psychosomatic Medicine. 2002;64(1):71-83.
28. O’Neal H, Dunn A, Martinsen E. Depression and exercise. International Journal of Sport Psychology. 2000;31(2):110-135.
29. The Medical Basis of Depression, Stress, Anxiety, Sleep Problems, and Drug Use. Available at http://www.teachhealth.com. Accessed July 26, 2002
Sponsored by the UAMS College of Medicine, Department of Psychiatry’s Partners in Behavioral Health Sciences program which is made possible by support from a Science Education Partnership Award (R25 RR15976) from the National Center for Research Resources at the National Institutes of Health.