High stress can blur memories and trigger a more general fear response. Now, scientists may have just discovered why.
Study using mice published Friday (November 15) in the journal cell, Suggests that stress hormones can distort the state of the body memory are recorded, making your memory less accurate and prone to being unable to properly distinguish between safe triggers and threats in the future.
The new findings could help reveal new avenues for treating people with post-traumatic stress disorder (PTSD) and generalized anxiety disorder.
“This is the best study to answer a long-standing unanswered question: how traumatic or highly stressful experiences promote the generalization of fear.” Dennis KaiAssociate Professor of Neuroscience at the Icahn School of Medicine at Mount Sinai, who was not involved in the study, told Live Science via email.
Scientists have long known that acute stress changes how memories are encoded, the study's lead author said. sheena jocelyna memory researcher at the Hospital for Sick Children and the University of Toronto.
For example, a person exposed to gunfire may later feel intense fear after a loud noise, which is an inappropriate response. This is called overgeneralization of fear.
Josselyn and her colleagues set out to understand what happens in the brain as these memories are formed.
They restricted the movements of the mice for 30 minutes, which was an extremely painful experience for the rodents. The mice were then trained to recognize two specific noises: one that preceded an unpleasant electric shock and one that did not. As expected, the stressed mice had a poor memory of noise and instead became afraid of many sounds.
A close look at the brains of these mice shows that stress affects the “engrams” of traumatic events, the physical traces of memory left behind when groups of neurons change to encode memories. It became clear that there was.
Typical engrams use a small number of brain cells and tend to be very “sparse,” Jocelyn told Live Science. She says this keeps memories from getting jumbled together. However, the researchers found that when people were exposed to stress, their engrams grew larger.
This is because high stress blocked inhibitory interneurons, cells that normally regulate the excitability of other neurons. The study found that these cells normally act as gatekeepers that limit the number of neurons that are looped into an engram.
“They're like nightclub bouncers who keep the bad guys out. Only the most excited neurons are allowed into this nightclub and become part of the engram,” Jocelyn said.
Stress triggers the release of corticosterone, the mouse equivalent of the human stress hormone cortisol, which triggers the release of neurotransmitters called endocannabinoids, which block the actions of inhibitory interneurons.
The fact that more neurons encode traumatic memories is both why these memories become vague and why people tend to overgeneralize fear from the original event to other experiences. may be explained.
Importantly, administering metyrapone, a chemical that inhibits corticosterone synthesis, before the mice were exposed to stress reversed the effect without altering the memory of the original stressful event. .
Since the research was conducted ratJocelyn said it's not yet clear whether the results can be applied to humans.
Still, this study provides insight into how stress can lead to memory overgeneralization, allowing researchers to counteract that effect without affecting other memories. Cai said this could help develop targeted treatments.
“This has huge implications for mental health disorders such as PTSD and generalized anxiety disorder,” she says.
Jocelyn said the study also raises questions about the use of cannabis in the context of PTSD.
Several clinical trials are investigating whether cannabinoids or cannabis products can treat PTSD and other anxiety disorders, but the field is still in its infancy. As a result, the U.S. Department of Veterans Affairs recommends against using cannabis products to treat PTSD. Still, anecdotal reports suggest that some people with PTSD probably use cannabis to self-medicate, Jocelyn said.
“People use a lot of cannabis for recreational and semi-medical purposes, but the scary thing is that many of the effects of cannabinoids in PTSD are not really understood,” she says. “So this definitely needs to be studied.”
