Stress and Memory
Short-term stressors of mild to moderate severity enhance thinking, while enormous or prolonged exposure to stress is disruptive to cognition.2 With short-term stress, the sympathetic nervous system kicks into gear, pouring epinephrine and norepinephrine into the bloodstream. Glucose is dumped into the bloodstream, and there is increased blood flow to the brain.2 Glucocortoids, released by the adrenal glands adjacent to the kidneys, are mildly elevated. The hippocampus, the part of the brain responsible for placing and retrieving memories in the cortex, is extremely sensitive to glucocortoid levels. 2,15 With increased glucocortoids available during stress, memories are retrieved more quickly. Levels of glucocortoids vary with the time of day, generally highest in the morning at around 6-8 am and lowest around midnight.15 Another part of the brain, the amygdala, also influences memory storage and recollection by releasing hormones.16 While the hippocampus mediates conscious memories, the amygdala mediates unconscious memories and the way your body responds based on past experiences.17
In the case of big stressors or long-term stress, an enormous amount of sympathetic arousal disrupts the potential of the hippocampus.2 After about 30 minutes of stress and prolonged exposure to glucocortoids, the hippocampus neurons take up about 25% less glucose, so the energy supply is decreased.2 Glucocortoids actually begin to damage neurons in the hippocampus, reducing its volume by up to 14%.2,16,17 The end result is that under high or prolonged stress, memory and concentration are impaired.2 However, at the end of the stressful period, it appears that neurons can regenerate their connections.2
Victims of abuse have been found to have 5% reduction in volume of the hippocampus. People with smaller hippocampi are more likely to suffer post-traumatic stress disorder.16 In addition, it has been shown that memory performance of both older adults and young adults can be significantly altered by manipulating glucocortoid levels.17 Overall, it can be concluded that experiences cause a chemical change within the brain which alter the structure of the hippocampus.16
Current implications in research indicate that high glucocortoid levels increase damage if another neurological insult is added, such as Alzheimer’s, AIDS, epileptic seizure, or stroke.2 Unfortunately, doctors often prescribe synthetic glucocortoids to stroke patients in an attempt to reduce inflammation, and
they are often prescribed to AIDS patients to combat various aspects of the disease. But, the result may well be greater damage to the hippocampus and increased likelihood of dementia and memory loss.2
Stress and Aging
As people and other organisms age, their epinephrine, norepinephrine, and glucocortoid levels rise in the normal resting state when there are no stressors present.2 When there is a stressor, levels rise higher than they do in younger people, but the body is less responsive to them. After the stressor is gone, the levels of these hormones do not return quickly to pre-stress levels. Therefore, it takes older people and organisms longer to recover from stress.2
Glucocortoids cause aging of many of the body’s systems. As we get older, our ability to regulate glucocortoid levels in our bloodstream degenerates.2 The hippocampus loses a considerable number of neurons which affects the brain’s ability to control glucocortoids. Increased glucocortoid levels damage the neurons in the hippocampus which, in turn, impedes the feedback for controlling glucocortoid levels. One theory as to why this happens is that perhaps memories actually serve to slow us down.16 Reliance on the amygdala to signal the brain that there is danger and a need for survival tactics, without interference from the hippocampus, may be more adaptive from a flight-or-flight standpoint.16
Fortunately, many humans and other organisms age successfully in a way that spares them the cascade of hippocampal destruction.2 Not enough is known yet to understand how this works in humans, but it appears possible that a lifetime of severe stress or heavy long-term use of synthetic glucocortoids to treat some disease may accelerate aspects of this cascade.2
This concludes our overview of how stress affects various systems of the body. In the next article we will discuss the psychological and social factors that modulate the stress response of the body. In the final article we will share strategies for managing and coping with stress.
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This article and all of our articles are intended for your information and education. We are not experts in the diagnosis and treatment of specific medical or mental problems. When dealing with a severe problem, please consult with a healthcare or mental health professional and research the alternatives available for your particular diagnosis prior to embarking on a treatment plan. You are ultimately responsible for your
own health and treatment!