One of the lead authors, Sheena A. Josselyn, a neuroscientist at the University of Toronto, notes: “A little stress is good; it’s what gets you up in the morning when your alarm goes off, but too much stress can be very disabling. Patients with PTSD may experience and display fearful reactions to situations or environments that are safe. We sought to limit this fear response to at least the specific situations that cause PTSD.”
A stressful event that recurs inevitably leads to stress again, because the brain associates it with the first unpleasant experience. This type of stress is linked to a memory. But stress caused by traumatic events like violence or generalized anxiety can spread far beyond the original event, something experts call
generalization of aversive memory induced by stress.
So, different stimuli can also trigger frightening memories and recreate stress or anxiety. In the case of PTSD, this can lead to severe negative consequences.
A better understanding of this process of memory generalization can inspire concrete therapies for different psychiatric disorders and other brain disorders, underline the researchers who propose here a promising new approach to restore “healthy” memory in patients suffering from the syndrome. post-traumatic stress disorder (PTSD).
The study seeks to identify the biological processes behind this stress-induced generalization of aversive memory and thus suggests an intervention that could help treat patients with PTSD:
The research team exposed mouse models to acute, but harmless, stress to create a fear memory that could be triggered by unrelated harmless situations, similar to how PTSD develops in humans. ‘Man ;
- examination of memory engrams or memory traces (physical representations of a memory in the brain) shows that these stress-induced memories involve many more neurons than other types of memories;
- it is these larger engrams that reproduce generalized fear memories even in harmless or unrelated situations;
- stress actually induces an increase in the release of endocannabinoids (endogenous cannabinoids) which disrupts the function of interneurons, whose role is precisely to limit the size of the engram.
The endocannabinoid system in fact participates in the formation of memory and makes it possible to link lived experiences to specific behaviors. In the amygdala, the emotional processing center of the brain, certain “guardian” interneurons have special receptors for endocannabinoids and help limit the size of the engram and the specificity of the memory.
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But, when too many endocannabinoids are released, the function of the guardian interneurons is disrupted, causing the engram to increase in size.
The team then shows that blocking endocannabinoid receptors on interneurons limits the generalization of aversive memory induced by stress;
“By blocking these endocannabinoid receptors only on these specific interneurons, we could essentially prevent one of the most debilitating symptoms of PTSD”conclude the scientists, who are now looking at how daily stressors can impact happy memories.
“Many biological functions and processes that make up the complexity of human memory remain to be discovered”…
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