Emotional experiences are easy to remember, but if the experience is too tragic, it can lead to PTSD and memory impairment. Stress is the physical and mental response to external stimuli, and the hippocampus, which functions as the memory center in the brain, can atrophy due to strong stress. I will explain in detail the relationship between stress-induced memory impairment and the hippocampus.
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memory loss caused by excessive stress
In “The suspension bridge effect improves memory? Why do you remember less intense experiences? ”, we found that memories of experiences that change emotions, such as happiness and fear, remain strong, and the neurotransmitter dopamine is part of the mechanism. I explained the possibility that However, it is also known that when there is too much emotional movement, memory impairment occurs conversely.
If it is a light stress that you feel in your daily life, you can resolve it yourself, but if you suddenly experience a shocking experience, it will cause extreme stress, and you will not be able to cure it by yourself. It may also invite Some of the victims of the Great Hanshin-Awaji Earthquake, the Tokyo subway sarin attack, the 9/11 terrorist attacks in the United States, the Great East Japan Earthquake, etc. suffered from emotional trauma due to strong stress and suffered from post-traumatic stress disorder (PTSD). It’s better to have a disease called.
PTSD is accompanied by persistent anxiety, insomnia, and memory problems. Memory impairment in people with PTSD appears to be an inability to remember or an inability to remember the traumatic event. Although such disorders have been known for some time, they were not considered diseases and were not actively treated. In recent years, as tragic disasters and incidents, as well as child abuse, have become a social problem, PTSD is regarded as a disease, and it has come to be thought that proper treatment should be done. This time, I will explain why painful experiences cause memory impairment.
Memory impairment in PTSD patients may be due to hippocampal atrophy
In 1995, Dr. J. Douglas Bremner and his colleagues at Yale University School of Medicine in the United States investigated changes that occurred in the brains of veterans engaged in the Vietnam War using MRI, one of the brain imaging techniques. They found that hippocampal volume decreased on average by 8% in 26 people with PTSD compared to 22 people without PTSD ( Am J Psychiatry, 152: 973 ). -981, 1995 ). At this time, since there was no difference in other brain regions, it was thought that PTSD causes atrophy not in the entire brain but in the hippocampus in particular.
In the following year, 1996, Dr. Tamara V. Gurvitz of Harvard Medical School in the United States conducted a follow-up study on seven Vietnamese veterans with PTSD, and found that the frequency of combat engagement was proportional to the degree of hippocampal atrophy. reported ( Biol Psychiatry, 40: 1091-1099, 1996 ).
In 1997, Dr. Bremner et al. also investigated 17 adult female patients who developed PTSD due to physical or sexual abuse in childhood, and found that hippocampal withdrawal decreased by an average of 12%. ( Biol Psychiatry, 41: 23-32, 1997 ).
Since then, many similar cases have been reported, so it seems safe to assume that the memory impairment seen in PTSD patients is related to hippocampal atrophy.
In the first place, stress is a reaction to adapt to external stimuli.
There are surprisingly few people among you who can properly explain the meaning of the word stress. Some of you may be. In order to deeply understand the relationship between stress and memory impairment, it is necessary to understand the nature of stress.
Stress is a term originally used in physics to refer to a state in which an object is distorted by an external force. This was used by American biologist Walter B. Cannon to explain the mechanism of the human body, and later developed by Canadian medical scientist Hans Selye, advocating the “stress theory” in 1936. Since then, the word “stress” in its current sense seems to have spread.
In the fields of current medicine and psychology, an external stimulus applied to the mind and body is called a stressor, and various reactions that occur in an attempt to adapt to the stressor are called stress reactions. It is important to properly use the words stressor and stress, so please master them properly. People often say things like, “Work is hard and stressful,” but that’s not true. It is correct to say that “hard work is a stressor” or “work is a stressor.”
As long as we live, we will always respond in some way to external stimuli. It’s no exaggeration to say that if you don’t react, you’re not alive. So everyone experiences stress all the time. There is no such thing as “stress-free” in the correct sense. Remember that stress is never a bad thing.
The action of nerves and hormones that try to resist stressors
Nerves and hormones work when our minds and bodies respond to stressor stimuli.
For example, just before I have to give an important presentation at a meeting, I get nervous and my heart starts pounding. From now on, you will have to use your body and mind actively, and in order to prepare for that, the sympathetic nerves will be activated and the heart will be pumped. So it’s a good thing because it’s proof that you’re preparing for what’s to come. Many people tend to think that they shouldn’t be nervous, but being nervous is never a bad thing. If you’re really nervous, you’ll be able to fight right away in the real thing, so let’s have confidence.
When the state of tension continues for a little longer, hormones collectively known as “glucocorticoids”, which are a type of adrenocortical hormone, are secreted from the organ called “adrenal glands” located above the kidneys. As the name suggests, this hormone raises blood sugar levels by stimulating the synthesis of glucose in the liver. If you continue to be tense, your body will need more and more energy.
In this way, the sympathetic nerves are activated and glucocorticoids are secreted from the adrenal glands when you are tense, to protect your mind and body against stressors.
However, if the stressor is too strong or lasts for a long time, the mind and body will not be able to handle it. We describe this state as “stressful and painful”.
Nerve cells die due to stress response and the hippocampus becomes smaller
Hormones travel long distances in the bloodstream and have various effects throughout the body. For more information, please read ” “Brain hormones” do not exist! Also see Differences Between Neurotransmitters and Hormones .
When the stress response continues and large amounts of glucocorticoids are secreted, it also affects the brain. In particular, there are glucocorticoid receptors in the hippocampus, and when these signals are received, hippocampal neurons are unnecessarily excited and damaged. In extreme stress disorders like PTSD, neurons die one after another and the hippocampus shrinks. As a result of the hippocampus not working, we fall into memory impairment.
Is memory impairment associated with PTSD a “last mile” to protect yourself?
The hippocampus is highly sensitive to stress and easily damaged, so it goes without saying that it is best to avoid excessive stress as much as possible. Since the avoidance method is introduced in various places, I dare not describe it here.
Rather, as a neuroscience researcher, I would like to conclude this article by considering why the hippocampus is so sensitive to stress.
Do you want to remember it forever when you have a painful experience? The tragic scenes of disasters, the abusive words, and violence received from immediate family members, etc… I think that I would like to forget such things if possible. When you are in a state of excessive stress, through the action of hormones, the memory system of the hippocampus is shut down so that you do not leave bad stressor memories. In this way, the memory impairment associated with PTSD may be the “last mile” to protect oneself.