Whether transient or sustained, the physiological stress response alters the memory, causing difficulties in retaining new information and recovering established memories.
However, the effects of stress on memory can be somewhat contradictory and differ depending on whether we are talking about acute or chronic stress.
Relationship between stress and memory loss
When the demands of the situation in which we find ourselves exceed our physical and/or cognitive capacities, our organism activates the stress response. This consists of the release of glucocorticoids, the stress hormones, into the bloodstream.
Glucocorticoids have different effects on the body, including an increase in heart and respiratory rate, a reduction in gastrointestinal activity and the release of stored glucose reserves for use as an energy source.
If their concentration is excessive, glucocorticoids, among which cortisol stands out, can have a negative effect on the functions of the hippocampus, a brain structure associated with the formation and recovery of memories. This is partly because glucocorticoids redirect glucose from the hippocampus to nearby muscles.
Two types of stress have been described according to their origin: extrinsic and intrinsic . Extrinsic stress is caused by non-cognitive factors, such as those arising from a given situation, while intrinsic stress is related to the level of intellectual challenge required by a task. Some people present chronic intrinsic stress.
Stress interferes both with our ability to retain new information and to recover memories and knowledge, leading to memory loss. In addition, extrinsic stress seems to affect spatial learning. In the following sections we will describe these effects in more detail.
Yerkes-Dodson’s Law: The Inverted U
Yerkes-Dodson’s law states that stress does not always interfere negatively with cognition , but that a moderate degree of brain activation improves memory and performance on intellectual tasks. In contrast, excessive increases in stress levels worsen cognitive functions.
This gives rise to the so-called “inverted U effect”: if our organism responds to environmental demands with mild or moderate stress responses, the effectiveness of our productivity increases until it reaches a threshold (the ideal activation point) beyond which performance progressively decreases and memory loss occurs.
Overly intense stress responses interfere with the performance of intellectual tasks because they are associated with physical and cognitive symptoms such as concentration difficulties, tachycardia, sweating, dizziness, or hyperventilation.
Effects of acute or transient stress
When we find ourselves in a stressful situation our attention is focused on the most salient stimuli, while we pay less attention to the rest; this phenomenon is known as “tunnel vision” and facilitates the consolidation of some memories while interfering with that of others, causing memory loss.
Acute stress can have beneficial effects on some types of memory but only under certain conditions. In this sense, the Yerkes-Dodson law should be mentioned again; on the other hand, some studies have shown that glucocorticoids improve the formation of new memories but worsen the recovery of existing ones.
In addition, emotionally relevant stimuli are better remembered if the stress response has occurred before, if information retrieval takes place soon after coding, and if the memory situation is similar to that of learning.
Other research suggests that under conditions of stress, we learn and remember more information and situations that cause us emotional distress. This fact is associated with the mood congruence effect described by Gordon H. Bower, who describes similar results in relation to depression.
Consequences of chronic stress
The stress response not only involves changes in memory at the time it occurs, but if chronically maintained, can cause long-term damage to the brain. Since the organism consumes many resources and reserves in the activation of these physiological processes, chronic stress is significantly more harmful than acute stress .
After situations of acute or transitory stress our body recovers homeostasis, that is to say, physiological balance; on the other hand, chronic stress prevents the organism from reaching homeostasis again. Therefore, if stress remains, the body’s responses are unbalanced.
From a physiological point of view, this facilitates the appearance of symptoms such as abdominal, back and headaches, chronic difficulties in concentrating and in falling or staying asleep, crises of distress, etc. In addition, continuous stress is associated with social isolation, depression and the development of cardiovascular diseases.
As for memory loss, chronic stress increases the risk of dementia in the elderly. These effects are probably related to the activity of glucocorticoids in the hippocampus and other regions of the brain on which memory and cognition in general depend.