Stress changes the way the brain stores memories, causing confusion between neutral and threatening situations, particularly in people suffering from post-traumatic stress, researchers say.
- A new study reveals how stress can broaden aversive memories, making safe situations frightening, such as in post-traumatic stress disorder (PTSD).
- Researchers have found that stress increases the release of endocannabinoids, disrupting the interneurons that limit the size of engrams, the brain’s memory structures. This generates generalized and inappropriate memories.
- By blocking these receptors, they reduced this phenomenon in preclinical models. This advance promises new therapies for PTSD, targeting memory with greater precision.
Why do certain stressful memories take on a disproportionate magnitude, to the point of resurfacing in otherwise harmless situations and triggering totally disproportionate reactions? A new study, led by neuroscientists from Hospital for Sick Children (SickKids) in Canada, today sheds light on the biological mechanisms behind this phenomenon, known as generalization of stress-induced aversive memories. Their results, published in the journal cellare paving the way for promising new treatments for people suffering from post-traumatic stress disorder (PTSD).
The influence of acute stress on memories
Memories are physically stored in the brain in the form of engrams, specific sets of neurons activated during an event – these are, in other words, the biological traces of memory. In normal situations, these engrams are restricted to a small group of neurons. But researchers have found that stress modifies this process, by considerably increasing the size of the engrams. These “expanded engrams” lead to generalized memories that manifest in harmless contexts, such as the sound of fireworks which will echo a trauma.
The SickKids team has identified a key player in this amplification of memories: endocannabinoids, natural brain substances that regulate many functions, including memory. In cases of acute stress, the excessive release of endocannabinoids disrupts the functioning of interneurons, the cells responsible for limiting the size of engrams. “Endocannabinoid receptors act as a selective barrier. When this barrier falls, the brain forms broader, poorly targeted aversive memories”can we read in a press release.
However, by blocking these receptors on interneurons in a preclinical model, researchers have succeeded in limiting the generalization of stressful memories. This advance could reduce a key symptom of PTSD that is particularly debilitating: inappropriate fear responses to safe situations.
Towards personalized therapies against post-traumatic stress
The implications of this discovery are vast. By 2023, previous research had shown that memories in developing brains naturally exhibit larger engrams, a phenomenon comparable to those induced by stress. This observation could provide a better understanding of how memories are formed at different stages of life, and how daily stress can alter positive memories.
Scientists point out that “the multiple biological processes linked to human memory are still largely unknown”. By revealing the mechanisms of the generalization of aversive memories, this research therefore opens the way to more targeted treatments against PTSD and other psychiatric disorders linked to stress and memory. If these findings translate into clinical therapies, they could transform the way millions of people deal with traumatic memories.
