When faced with a menacing threat, your brain's stress response system harnesses your body's energy resources in order to help you get out of harm's way. In the short-term, this response keeps you safe. If, however, your stress response system is subjected to constant danger, whether real or perceived, your mental and physical health could be at risk.
The Stress Response
If you need to escape a burning building or meet an impending deadline, the brain's fight or flight response gives your muscles the extra energy they need to ensure your survival. In the face of danger, a section at the base of the brain called the hypothalamus sends signals to the adrenal glands, which are located just above the kidneys, to release the stress hormones adrenaline and cortisol. These hormones increase the heart rate and blood pressure and also elevate blood glucose levels, your muscles' energy source. Cortisol also temporarily shuts down other body systems, like the digestive and reproductive systems, until the threat has passed.
Chronic Stress
When you are no longer in danger, the brain signals the parasympathetic nervous system to induce relaxation by suppressing the release of stress hormones and slowing the heart rate and blood pressure back down to normal levels. However, a chronically distressing situation can override the relaxation response and leave the body in fight or flight mode indefinitely. When this happens, the overabundance of cortisol and other stress hormones left in the system can wreak havoc on the brain and body.
Cortisol and Brain Damage
Extended exposure to high levels of cortisol can lead to the degeneration of the hippocampus, a region of the brain involved in memory and learning. Cortisol channels blood glucose to the muscles, which diminishes the amount of energy available to the hippocampus. Additionally, the hippocampus is partially responsible for turning off cortisol production after a threat has passed. Therefore, once it has been damaged by cortisol overexposure, it is less able to fulfill this function. This leads to a continuous secretion of cortisol and continual damage to this region of the brain.
Stress and Alzheimer's Disease
Chronic stress and anxiety can also make you more susceptible to Alzheimer's disease. In 2006, Washington University's David Holtzman exposed a group of rats to various lengths of chronic stress from three days to three months. After only three days, Holtzman found a 42 percent increase of amyloid beta peptide, a brain protein that have been linked to Alzheimer's disease. The rats that underwent three months of chronic stress had twice as much of the protein in their brain fluid as a control group.
Chronic Stress and Depression
Extended periods of stress can also lead to depression, according to a study conducted by Harvard University's Dr Kwang-Soo Kim. In the study, he exposed 58 mice with cortisol for either short or long periods of time. He then introduced the rodents to a new environment and observed their behavior. The mice that had experienced chronic cortisol exposure showed significant hesitation and fearfulness in the new environment, a behavior that indicates anxiety and depression. The study entitled, "Anxiogenic-like Effect of Chronic Corticosterone in the Light-Dark Emergence Task in Mice," was published in the April 2006 issue of the journal "Behavioral Neuroscience".
References
- Your Amazing Brain: Stress: Your Brain and Body
- Mayo Clinic: Win Control Over Stress In Your Life
- The Franklin Institute: How Your Brain Responds to Stress
- "The Hindustan Times"; Mechanism Behind Stess Leading to Alzheimer's Identified
- "Western Mail"; Stress Hormone Contributes to Symptoms of Depression; April 2006
