Everyday life can be filled with stressful situations. Giving a presentation at work, taking an important test, going on a first date-even thinking about the last time you felt “stressed out” can make you sweat a little and bring back the physical sensations that often go along with stress: muscle tension, a headache, an upset stomach, a pounding heartbeat.
It may feel uncomfortable at times, but stress serves a vital role in alerting our brains to important information about our environment and preparing our bodies to react appropriately. Feeling stressed about standing too close to a poisonous snake-and moving to a safe distance because of it-is a good example of how we use stress to protect ourselves from danger. Stressful situations can also cause the body to release adrenaline, a process that facilitates attention to important details and can produce vivid memories by helping the brain record them in long-term memory.
Stress has its benefits, but a growing amount of scientific research also suggests that long-term exposure to chronic stress can have a significant negative impact on learning and memory.
How the Brain Responds to Stress
The brain has a sophisticated chemical system designed to react to stress. When the brain perceives a threat-whether it’s a looming deadline at work or bee that’s just landed on your arm-the body’s sympathetic nervous system activates the fight-or-flight response, a jolt to the adrenal glands that releases a flood of hormones including epinephrine (also called adrenaline) and norepinephrine. These hormones trigger physical changes in the body, such as increased heart rate, higher blood pressure, and faster breathing, which provide the body with plenty of energy and oxygen to respond to the threat at hand.
The hormones released into the bloodstream during times of stress also affect the brain and the ability to remember. The entire nervous system responds to stress, but the brain’s limbic system plays a particularly important role. The limbic system includes the hypothalamus, the hippocampus, the amygdala, and other important brain structures that govern emotional responses, behavior, and long-term memory. The release of adrenaline increases levels of activity in these areas of the brain and has been associated with improved memory.
When Stress Does More Harm than Good
Stress has important benefits-helping us stay alert and avoid danger-but exposure to chronic stress can have negative effects on the body, leading to sustained high blood pressure, increased abdominal fat, and decreased bone density. It can also damage the brain, particularly the hippocampus, and impair the ability to remember.
When we feel stressed, the adrenal glands release epinephrine and norepinephrine, but they also release steroid hormones called glucocorticoids-more commonly known as corticosteroids or cortisol-into the bloodstream. The hippocampus has a high density of receptors for glucocorticoids, and under normal circumstances the sea-horse shaped organ helps regulate the production of the stress hormones.
However, the hippocampus is particularly sensitive to these hormones. Studies have shown that the hippocampal neurons of rodents die when they are exposed to glucocorticoids for months, and that neuronal dendrites atrophy and retract after just a few weeks of stress. As a result of the damage, stress hormones continue to be secreted at increased levels, resulting in even more damage to the hippocampus.
Recent research has also shown that short-term stress can damage the brain, taking minutes-not months-to impact neurons responsible for learning and memory. Scientists at the University of California, Irvine, found that acute stress activates selective molecules called corticotropin releasing hormones. Like cortisol, these hormones disrupt the process by which the brain collects and stores memories.
Because exposure to stress can damage the hippocampus, and since the hippocampus is an important brain structure associated with declarative memories for facts, researchers have been particularly interested in how stress affects our ability to remember new information.
Studying Stress in the Human Brain
Studies have shown that rats exposed to high levels of stress hormones have memory deficits. Researchers who want to study the link between stress and memory in healthy human beings have several options. They can expose people to doses of stress hormones, create experiences in their laboratories that are stressful for participants, or they can study the memory performance of people who have experienced stressful events like war, severe accidents, or the death of a loved one.
In fact, a growing number of these kinds of studies have shown that stress negatively effects declarative memory. For example, researchers at Washington University School of Medicine found that participants who were given doses of cortisol at levels corresponding to times of moderate or major stress were not able to remember as much information from short paragraphs as study participants who were given placebos. The effect went away after a six-day “washout” period, suggesting it is reversible.
The effort required to suppress thoughts about stressful life experiences like a death in the family or starting a new job may also affect our ability to juggle and make use of multiple pieces of incoming information. Psychologists have found that the more negative life stress participants reported-and the more time they reported thinking about those events-the poorer was their performance on difficult working memory tasks.
Stress is an inevitable part of life, so learning how to cope with stressful situations and manage the body’s responses to them is key. Deep breathing, meditation, exercise, and spending time with family and friends have all been shown to reduce stress. It may take some effort, but setting aside some time to relax will benefit both the body and the brain.
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