Stress and The Brain
Stress - particularly chronic stress - can have a profound impact on the brain and its overall function. Individuals who experience high levels of stress frequently also report such things as forgetfulness or being overly emotional.
Studies show that stress over life events can affect the autonomic nervous system, the hypothalamic-pituitary-adrenal axis, and the immune system. McEwen (1998) refers to the long-term effects of chronic over-activation of the physiological systems as "allostatic load." Scientists are only now addressing how the brain is affected by stress. The following are elements that Paper Masters suggests when writing research on stress and the brain:
- Explore the research on negative impact of the brain due to prolonged stress. Reveal general findings and known stress responses will lay the groundwork toward understanding the issue.
- Investigate known effects of hormones and other chemicals related to stress will be discussed in terms of how they affect mood or trigger depression.
- Research regarding Post Traumatic Stress Disorder and other causes of stress and their effects will be reviewed.
Research has shown that when a person is stressed, the electrical signals in their brain focus on emotions rather than factual memories. Individuals are also less capable of making rational decisions when they are experiencing a period of increased stress. This state also contributes to the vicious cycle that is stress causing fear and anxiety, which in turn causes more stress. When a person is stressed, their amygdala increases in size and activity; this creates a greater sense of fear and anxiety, which only feeds into the factors that cause the changes in the amygdala.
Hormonally, when a person experiences stress, their body produces more levels of cortisol. This hormone can have profound implications on the brain, including impact the ability of the brain to produce more cells. A protein known as brain-derived neurotropic factor (BDNF) allows for the creation of new brain cells; cortisol, when present, prevents BDNF from being created, which in turn prevents the creation of new brain cells. Research has also shown that when levels of BDNF decline, there is a greater likelihood of other health problems, ranging from Alzheimer's disease to schizophrenia to depression.
In the past, theorists assumed that the generality model of stress was most accurate. This model maintained that all stressors triggered stereotyped physiological responses in all people. Modern stress researchers understand, however, that the relationship between stressors and effects is moderated by the specific stressful conditions, the qualitative appraisal of the situation, and the distinct emotional and physiological responses in each person. Furthermore, the effects of stress are multi-directional. For instance, immune cell products may affect the brain. This may lead to altered mood and cognition, which may contribute to depression. People who are depressed may over-react to stressful events. The cycle continues.
The human body has evolved several support reactions that allow for survival in threatening situations. For instance, our ancestors, when confronted with a ferocious beast, needed to respond immediately and efficiently. Their bodies reacted by mobilizing necessary physiological systems and suppressing systems that were unnecessary at the moment. Therefore, upon seeing the attacking animal, their bodies would increase the available concentrations of glucose to ready the body for running. This response continues to today, although instead of saber-toothed tigers, stressors may be traffic, relationships, noise, or many other modern hassles. Immediate and temporary reactions to stress have no long-term consequences. However, chronic activation of these systems can have adverse long-term physiological and health effects.
Studies have long confirmed that the constant use of neuroendocrine and central nervous transmitter systems is damaging to the body. Chronic stress has been shown in animal studies to induce changes in neuroendocrine and neuronal systems, including changes in size of brain nuclei, in morphology of neurons, and in neurotransmitter and second messenger systems. The body of research on the issue shows that the body cannot regenerate these functions after the damage has occurred.
In response to stress, the hypothalamus is one area of the brain that is called into action. The rapid response of the brainstem and the hypothalamus circumvents the relatively slower cognitive processing in the limbic and cortical areas of the brain (Fuchs & Flugge, 2003). This structure contains collections of neurons that regulate sleep and appetite, as well as control several hormones. Critical to our management of stress is the paraventricular nucleus. This collection of neurons secretes corticotrophin-releasing hormone (CRH) which triggers the stress reaction. This is managed in two ways. First, it signals other organs by releasing a hormone. This signal reaches the pituitary gland in the brain and the adrenal glands in the kidneys. This function is known as the hypothalamus-pituitary-adrenal axis. In response, the pituitary releases adrenocorticotropic hormone (ACTH) into the bloodstream. This signals the adrenal glands to release glucocorticoid hormones into the blood. These hormones increase glucose levels to provide energy. The hypothalamus monitors these hormone levels and continually sends out signals to regulate them.