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A stressor is anything that threatens the body’s homeostasis, that disturbs its balance point. Our bodies are best designed to deal with acute stress and poorly designed to tackle chronic stress. The stressor does not have to be real to evoke a stressful response. You can be sitting on a chair and have thoughts that could activate your stress response. So, your nervous system generates all this energy to prepare you to run away but you are still sitting in your chair.
There are two parts to the stress response: fast and slow. An immediate response to a threat is activation of the sympathetic nervous system SNS, which speeds up the heart, dilates eyes, slows digestions and free up energy. The slower response results in the release of glucocorticoids which affect sensory, memory and cognitive systems.
Acute stressor, short-term stress.
During a short-term stressor, our general cognition including memory becomes sharper. Imagine that you are in a dark forest by yourself. The stress response commences by activating your SNS. It increases your survival by lowering sensory threshold so you can quickly react should an attack take place. Your vision becomes sharper, so you can quickly spot any potentially moving beings. Your hearing threshold is lowered so you can quickly assess faint noise in the bush. There is also an increase in decision-making abilities that is facilitated by slowing down in time. SNS also indirectly wakes up the hippocampus, the key player in consolidation of memories into long-term. Also, these enhancements in sensory and cognitive faculties and brain memory areas give rise to well-encoded memories. Many situations that evoke our stress response produce well-remembered events. When researchers pharmacologically block our sympathetic nervous system, the stress facilitated memory formation goes away.
Chronic stress: If stress goes on and on?
In chronic stress, the body’s adaptive strategies become destructive. The most deleterious effects of chronic stress impact the hippocampus and related memory areas. A part of the stress response is the release of glucocorticoids (you might know of cortisol). With chronic stress, this hormone accumulates and cause brain toxicity. In short-term stress, low to moderate amounts of glucocorticoids cause the hippocampus to efficiently function and consolidate events into long-term memory storage. However, excessive amounts of glucocorticoids activate the quieter receptors which leads to havoc when activated. These hormones interfere with the ability of the hippocampal neurons to communicate and thus a memory fails to form. In addition, excessive stress hormones encourage the forgetting circuits of the hippocampus, so other memories get deleted. Not surprisingly, in disorders related to elevated glucocorticoids such as depression, patients complain of memory problems.
In addition, emotional or highly arousing events (such as stressful ones) typically activate the amygdala. The amygdala is intimately connected with the hippocampus. During a highly disturbing event, the amygdala sends powerful messages to the hippocampus that also impede the formation of memories. In disorders where the amygdala is hyperactive such as anxiety, patients (not surprisingly) complain of memory problems.
There are a few areas in our nervous system where neurogenesis (birth of new cells) can continue during adulthood, such as the hippocampus. The high levels of glucocorticoids that accompany chronic stress inhibit the birth of new neurons in the hippocampus. Lastly, these high levels can kill hippocampal cells.
Memory loss may be a symptom of the toxic effects of chronic stress. Some people are more vulnerable to stress because of early childhood traumas or having certain personality types. Eventually, distortions in memory can affect relationships, careers, self-esteem, and confidence. Stress management might restore memory systems. Thus, if your memory loss is bothering you, search for a stress management routine that best suits your lifestyle.
