When people experience a traumatic event, they often carry very strong memories of the specific negative event but keep only vague memories of the surrounding context. This happens because the amygdala — the part of the brain used to store emotional memories — becomes more active during a negative event, while the areas that store neutral content become less active, according to a new study by researchers at University College London (UCL).
“When we presented people with negative content alongside neutral content, the brain areas involved in storing the negative content were more active while those involved in storing the surrounding context were less active,” explains lead author Dr James Bisby (UCL Institute of Cognitive Neuroscience).
“When we experience a new event, we not only store the contents of the event in memory, such as the people we met, but we also form associations with the context in which the event took place. The hippocampus is a crucial brain region for forming these associations so that all aspects of the event can be retrieved together and placed in the appropriate context, and it was here that we saw reduced activity.”
The study, published in the journal Social, Cognitive, and Affective Neuroscience, has important implications for understanding conditions stemming from negative events, such as post-traumatic stress disorder (PTSD).
“The imbalance between item memory and associative memory could lead to strong but fragmented memory for the traumatic content of an event, without the surrounding information that would put it in the appropriate context,” says senior author Professor Neil Burgess, Director of the UCL Institute of Cognitive Neuroscience.
“People who have suffered a traumatic event can experience vivid and distressing intrusive images from it, as in post-traumatic stress disorder. These intrusive images might occur due to strengthened memory for the negative aspects of the trauma that are not bound to the context it occurred in. This may be the mechanism behind ‘flashbacks’, where traumatic memories are involuntarily re-experienced as if they are happening in the present.”
For the study, 20 participants were placed in an MRI scanner and shown pairs of pictures to remember. Some of these pictures involved traumatic content such as a badly injured person.
The participants’ memories were then tested by being shown images while being asked if they had seen that image before. If they had, they were asked whether they could remember the other picture that had appeared next to it.
The findings show that the participants were better at remembering negative pictures compared to neutral ones. This was reflected by increased activity in the amygdala, a part of the brain used for processing emotional information. They also had a harder time remembering which other pictures appeared alongside negative ones, reflecting reduced activity in the hippocampus.
Source: University College London