Trials, strokes of fate or other stressful situations – even years later, people often have astonishingly detailed pictures of such experiences in front of their eyes. An experimental study now sheds light on the neural mechanisms underlying this intensified memory. The researchers were able to make it clear that objects perceived under stress are stored in the brain as connected to one another and that their processing is based on a similar activity as with memories of the stress trigger itself.
The pattern of ties, the colors of cups, the faces of those involved: people can often remember scenes and impressions in connection with stressful experiences such as an exam situation for a long time in astonishingly detail. The impressions of a walk through the park on the same day, on the other hand, are quickly forgotten. What is this difference about? Researchers at the Ruhr University in Bochum are investigating the background to this memory phenomenon. As they explain, in addition to providing fundamental insights into how the brain works, this research could also provide an understanding of psychological disorders associated with problematic – traumatic – memories.
Stress memories in sight
Basically, it is already known that the increased release of certain neurotransmitters in the brain plays a role in the increased memory performance in stressful situations. These messenger substances evidently cause changes in the neuronal representations during these experiences. Previous studies and theoretical considerations had so far led to different explanations for how memories of stressful experiences differ from neutral ones. In order to gain further insights, the Bochum scientists have now recorded the memory traces in connection with real stressful situations by means of a study with a total of 65 volunteers.
To ensure experimental stress, the so-called Trier Social Stress Test was used: In a fictitious job interview, the test subjects had to answer questions to two people who looked motionless and gave no positive feedback. In addition, they were demonstratively filmed in the situation. Subsequent saliva tests showed that this actually caused stress in the test subjects. During the unpleasant situation, a total of 26 objects could be seen in the room: from a garbage can to a Coke can to a fan. The “committee” used some “central objects”: For example, certain vessels were used to drink something. In the control group, the test subjects were confronted with the same objects and actions, but not exposed to any stress: It was a friendly conversation without video recordings.
Special features of stress become apparent
The day after the test, the researchers then showed the study participants in both groups the objects they saw while they recorded their brain activity in a magnetic resonance tomograph. The focus was on the amygdala – a brain region that is important for emotional learning, among other things. The comparison of the neural traces showed: In the control group, the nervous patterns in the case of the objects used in the relaxed conversation situation hardly differed from those in the non-central objects in the room. In the test subjects with the stress experience, however, the memory traces between the objects used and those not used differed significantly: Objects that were the focus of the stressful episode because they were manipulated by the experimenters had similar representations in the amygdala. That means: The neural anchoring of the important objects from the stressful situations appear grouped and are clearly separated from other impressions, the scientists explain.
In addition to the pictures of the objects from the application situation, they also showed the test subjects photos of the people on the application committee the day after the stress test. As the scientists explain, from a psychological point of view, they were not some kind of object in the context of the situation, but the stress triggers. The ability to remember and the comparison of brain activity when looking at the faces with those of the different objects showed that the test subjects remembered in particular those objects whose brain activity was similar to that triggered by the memory of the committee members. “It therefore seems that the connection between the objects and the stress triggers was decisive for the improved memory,” explains co-author Nikolai Axmacher.
As the researchers sum up, their study results now suggest: The mechanism that reinforces emotional memories is characterized by the fact that the important aspects of the respective scenario are linked to one another at the neural level and are then linked to the stress trigger. “This result could be an important building block for a better understanding of emotional and traumatic memories,” says first author Anne Bierbrauer.
Source: Ruhr University Bochum, specialist article: Current Biology, doi: 10.1016 / j.cub.2021.09.044