question: Why does continuous stress deteriorate the brain and neural connections?
comment: When you are stressed out your body and brain will release chemicals (stress hormones such as cortisol) which are meant to prepare your body for a fight or flight response. These chemicals break down tissues to increase blood sugar and provide the fuel needed for your response. Excessive exposure to these chemicals will therefore cause your tissues to breakdown to a point where they are not easily repaired, and this can cause long term neural and muscular damage, or even diabetes due increased blood sugar.
passages: Through these mechanisms, stress can alter memory functions, reward, immune function, metabolism and susceptibility to diseases. Definitions of stress differ. One system suggests there are five types of stress labeled "acute time-limited stressors", "brief naturalistic stressors", "stressful event sequences", "chronic stressors", and "distant stressors". An acute time-limited stressor involves a short-term challenge, while a brief natural stressor involves an event that is normal but nevertheless challenging. A stressful event sequence is a stressor that occurs, and then continues to yield stress into the immediate future. A chronic stressor involves exposure to a long-term stressor, and a distant stressor is a stressor that is not immediate.
   Stress affects many memory functions and cognitive functioning of the brain. There are different levels of stress and the high levels can be intrinsic or extrinsic. Intrinsic stress level is triggered by a cognitive challenge whereas extrinsic can be triggered by a condition not related to a cognitive task. Intrinsic stress can be acutely and chronically experienced by a person. The varying effects of stress on performance or stress hormones are often compared to or known as "inverted-u" which induce areas in learning, memory and plasticity. Chronic stress can affect the brain structure and cognition.
   Section::::Long-term memory.
  
  Long-term memory (LTM) is the ability to store an unlimited amount of information over long periods of time, ranging from a few days to many years.
  
  Less is known about the effect of stress on LTM than is known about the effect of stress on STM. This could be due to the fact that LTM is not affected as severely as STM and WM are, and is also influenced by the effect of stress on STM and WM.
   Stress, to a physiologist, means any situation that threatens the continued stability of the body and its functions. Stress affects a wide variety of body systems: the two most consistently activated are the hypothalamic-pituitary-adrenal axis and the norepinephrine system, including both the sympathetic nervous system and the locus coeruleus-centered system in the brain. Stressors of many types evoke increases in noradrenergic activity, which mobilizes the brain and body to meet the threat. Chronic stress, if continued for a long time, can damage many parts of the body. A significant part of the damage is due to the effects of sustained norepinephrine release, because of norepinephrine's general function of directing resources away from maintenance, regeneration, and reproduction, and toward systems that are required for active movement. The consequences can include slowing of growth (in children), sleeplessness, loss of libido, gastrointestinal problems, impaired disease resistance, slower rates of injury healing, depression, and increased vulnerability to addiction.
   WM is affected to a greater extent by stress than LTM. Stress has been shown to both improve and impair WM. In a study by Duncko "et al.", the positive effect of stress manifested itself as a decreased reaction time in participants, while the negative effect of stress causes more false alarms and mistakes when compared to a normal condition. The researchers hypothesize that this could be representative of faster information processing, something helpful in a threatening situation. Anxiety has also been shown to adversely affect some of the components of WM, those being the phonological loop, the visuo-spatial sketchpad, and the central executive. The phonological loop is used for auditory STM, the visuo-spatial sketchpad is used for visual and spatial STM, and the central executive links and controls these systems. The disruption of these components impairs the transfer of information from WM to LTM, thus affecting learning. For instance, several studies have demonstrated that acute stress can impair working memory processing likely though reduced neural activity in the prefrontal cortex in both monkeys and humans.
   This type of stressor is unforeseen and unpredictable and, as such, is completely out of the control of the individual. Examples of crises and catastrophes include: devastating natural disasters, such as major floods or earthquakes, wars, etc. Though rare in occurrence, this type of stressor typically causes a great deal of stress in a person's life. A study conducted by Stanford University found that after natural disasters, those affected experienced a significant increase in stress level. Combat stress is a widespread acute and chronic problem. With the rapid pace and the urgency of firing first, tragic episodes of accidentally killing friendly forces (“brother” killing “brother” or fratricide) may happen. Prevention requires stress reduction, emphasis on vehicle and other identification training, awareness of the tactical situation, and continual risk analysis by leaders at all echelons.
   Chronic stress is a stressor that is ongoing for a long period of time. When chronic stress is experienced, our body is in a state of continuous physiological arousal. Normally, our body activates our fight-or-flight-response, and when the perceived stress is over our body returns to a state of homeostasis. When chronic stress is perceived, however, the body is in a continuous state of fight-or-flight response and never reaches a state of homeostasis. The physiological effects of chronic stress can negatively affect memory and learning. One study used rats to show the effects of chronic stress on memory by exposing them to a cat for five weeks and being randomly assigned to a different group each day. Their stress was measured in a naturalistic setting by observing their open field behaviour, and the effect on memory was estimated using the radial arm water maze (RAWM). In the RAWM, rats are taught the place of a platform that is placed below the surface of the water. They must recall this later to discover the platform to exit the water. It was found that the rats exposed to chronic psychosocial stress could not learn to adapt to new situations and environments, and had impaired memory on the RAWM.
   The major effect of stress on LTM is that it improves consolidation of memory, while it impairs the retrieval of memory. That is, one will be able to remember information relating to a stressful situation after the fact, but while in a stressful situation it is hard to recall specific information. In a study by Park "et al." done on rats, the researchers found that shock induced stress caused the rats to forget what they learned in the phase prior to the shock, but to have distinct memory for where the shock occurred. This negative effect on the retrieval of memories caused by stress can be attributed to cortisol, the stress hormone that is released in stressful situations.
   The immune system also plays a role in stress and the early stages of wound healing. It is responsible for preparing the tissue for repair and promoting recruitment of certain cells to the wound area. Consistent with the fact that stress alters the production of cytokines, Graham et al. found that chronic stress associated with care giving for a person with Alzheimer's disease leads to delayed wound healing. Results indicated that biopsy wounds healed 25% more slowly in the chronically stressed group, or those caring for a person with Alzheimer's disease.
  
  Section::::Effects of chronic stress.:Development.
   Daily hassles are the most frequently occurring type of stressor in most adults. The high frequency of hassles causes this stressor to have the most physiological effect on an individual. Carolyn Aldwin, Ph.D., conducted a study at the Oregon State University that examined the perceived intensity of daily hassles on an individual's mortality. Aldwin's study concluded that there is a strong correlation between individuals who rate their hassles as very intense and a high level of mortality. One's perception of his/her daily stressors can have a modulating effect on the physiological impact of daily stressors.
   The length of time since occurrence and whether or not it is a positive or negative event are factors in whether or not it causes stress and how much stress it causes. Researchers have found that events that have occurred within the past month generally are not linked to stress or illness, while chronic events that occurred more than several months ago are linked to stress and illness and personality change. Additionally, positive life events are typically not linked to stress and if so, generally only trivial stress while negative life events can be linked to stress and the health problems that accompany it. However, positive experiences and positive life changes can predict decreases in neuroticism.
   When humans are under chronic stress, permanent changes in their physiological, emotional, and behavioral responses may occur. Chronic stress can include events such as caring for a spouse with dementia, or may result from brief focal events that have long term effects, such as experiencing a sexual assault. Studies have also shown that psychological stress may directly contribute to the disproportionately high rates of coronary heart disease morbidity and mortality and its etiologic risk factors. Specifically, acute and chronic stress have been shown to raise serum lipids and are associated with clinical coronary events.
   In the nervous system, structural and functional abnormalities are a result of chronic prolonged stress. The increase of stress levels causes a shortening of dendrites in a neuron. Therefore, the shortening of dendrites causes the decrease in attention. Chronic stress also causes greater response to fear of the unlearned in the nervous system, and fear conditioning.
   No matter the magnitude of the stressor and stress, most stressor-stress relationships can be evaluated and determined by either the individual or a psychologist. Without proper attention, stress can produce severe effects on mental health and the immune system, which can eventually lead to effects on the physical body. Therapeutic measures are often taken to help replenish and rebuild the individual’s coping resources while simultaneously aiding the individual in dealing with the current stressor.
  
  Section::::Psychological Stressors.
   Chronic stress and a lack of coping resources available or used by an individual can often lead to the development of psychological issues such as delusions, depression and anxiety (see below for further information). This is particularly true regarding chronic stressors. These are stressors that may not be as intense as an acute stressor like a natural disaster or a major accident, but they persist over longer periods of time. These types of stressors tend to have a more negative effect on health because they are sustained and thus require the body's physiological response to occur daily.
   Short-term memory (STM) is the ability to store small amounts of information for a limited amount of time. The "Miller's Law" that the capacity of an average person's STM is 7±2 objects, and lasts for a matter of seconds. This means that when given a series of items to remember, most people can remember 5-9 of those items, the average being 7. However, this limit can be increased by rehearsing the information. Information in STM can be transferred to long-term memory (LTM) by rehearsal and association with other information previously stored in LTM.
   Chronic stress is a term sometimes used to differentiate it from acute stress. Definitions differ, and may be along the lines of continual activation of the stress response, stress that causes an allostatic shift in bodily functions, or just as "prolonged stress". For example, results of one study demonstrated that individuals who reported relationship conflict lasting one month or longer have a greater risk of developing illness and show slower wound healing. Similarly, the effects that acute stressors have on the immune system may be increased when there is perceived stress and/or anxiety due to other events. For example, students who are taking exams show weaker immune responses if they also report stress due to daily hassles. While responses to acute stressors typically do not impose a health burden on young, healthy individuals, chronic stress in older or unhealthy individuals may have long-term effects that are detrimental to health.
   Stress in early childhood can impede brain development of children that results in both physical and mental health problems. Healthy brain and physical development can be hampered by excessive or prolonged activation of stress response systems. Although both adrenaline and cortisol help prepare the body for coping with stressors, when they are used to prolonged and uncontrollable stress, this stress response system can lead to impairments in both mental and physical health.
   Chronic stress is unlike acute stress. It has a wearing effect on people that can become a very serious health risk if it continues over a long period of time. Chronic stress can lead to memory loss, damage spatial recognition and produce a decreased drive of eating. The severity varies from person to person and also gender difference can be an underlying factor. Women are able to take longer durations of stress than men without showing the same maladaptive changes. Men can deal with shorter stress duration better than women can but once males hit a certain threshold, the chances of them developing mental issues increases drastically.
   Conversely, reversal learning is inhibited by the presence of anxiety. Reversal learning is assessed through the reversal learning task; a stimulus and response relationship is learned through the trial and error method and then without notice, the relationship is reversed, examining the role of cognitive flexibility. Inhibited reversal learning can be associated with the idea that subjects experiencing symptoms of anxiety frustrate easily and are unable to successfully adapt to a changing environment. Thus, anxiety can negatively affect learning when the stimulus and response relationship are reversed or altered.
  
  Section::::Stress, memory and animals.
   This depletes the body's energy more quickly and usually occurs over long periods of time, especially when these microstressors cannot be avoided (i.e. stress of living in a dangerous neighborhood). See allostatic load for further discussion of the biological process by which chronic stress may affect the body. For example, studies have found that caregivers, particularly those of dementia patients, have higher levels of depression and slightly worse physical health than non-caregivers.
   Chronic stress affects a person's cognitive functioning differently for normal subjects versus subjects with mild cognitive impairment. Chronic stress and elevated cortisol (a biomarker for stress) has been known to lead to dementia in elderly people. A longitudinal study was performed which included 61 cognitively normal people and 41 people who suffered from mild cognitive impairment. The participants were between 65 and 97 years old. 52 of the participants were followed for three years and repeatedly received stress and cognitive test assessments. Any patient that suffered from signs or conditions that would affect their cortisol level or cognitive functioning was exempt from participating.
   Chronic stress has also been shown to impair developmental growth in children by lowering the pituitary gland's production of growth hormone, as in children associated with a home environment involving serious marital discord, alcoholism, or child abuse.
  
  More generally, prenatal life, infancy, childhood, and adolescence are critical periods in which the vulnerability to stressors is particularly high.
  
  Section::::Effects of chronic stress.:Psychopathology.
   Working memory is impaired by acute and chronic psychological stress. This phenomenon was first discovered in animal studies by Arnsten and colleagues, who have shown that stress-induced catecholamine release in PFC rapidly decreases PFC neuronal firing and impairs working memory performance through feedforward, intracellular signaling pathways. Exposure to chronic stress leads to more profound working memory deficits and additional architectural changes in PFC, including dendritic atrophy and spine loss, which can be prevented by inhibition of protein kinase C signaling. fMRI research has extended this research to humans, and confirms that reduced working memory caused by acute stress links to reduced activation of the PFC, and stress increased levels of catecholamines. Imaging studies of medical students undergoing stressful exams have also shown weakened PFC functional connectivity, consistent with the animal studies. The marked effects of stress on PFC structure and function may help to explain how stress can cause or exacerbate mental illness.
   It has long been believed that negative affective states, such as feelings of anxiety and depression, could influence the pathogenesis of physical disease, which in turn, have direct effects on biological process that could result in increased risk of disease in the end. However, studies done by the University of Wisconsin-Madison and other places have shown this to be partly untrue; although stress seems to increase the risk of reported poor health, the "perception" that stress is harmful increases the risk even further. For example, when humans are under chronic stress, permanent changes in their physiological, emotional, and behavioral responses are most likely to occur. Such changes could lead to disease. Chronic stress results from stressful events that persist over a relatively long period of time, such as caring for a spouse with dementia, or results from brief focal events that continue to be experienced as overwhelming even long after they are over, such as experiencing a sexual assault.
  