Stress intensifies unconnected memories

NYU (US) — Stress can enhance ordinary, unrelated memories, according to new research.

The findings may bolster understanding of post-traumatic stress disorder and offer a pathway for addressing PTSD and related afflictions.

“Our results show that stress can activate memory, even if that memory is unrelated to the stressful experience,” explains André Fenton, professor at New York University.

“Additional investigations into the effects of stress on memories could shed light on PTSD and other stress-related mood disorders.”

A common feature of PTSD and various mood and anxiety disorders is the formation of negative associations from otherwise innocuous stimuli or the recall of negative memories stimulated by unrelated, neutral circumstances.

What’s less clear is how stress influences these phenomena.

For the study, published in PLoS Biology, rats were taught to make distinctions between left and right in a T-shaped maze. One day later, the researchers induced stress in the rats through a commonly practiced technique—placing them in a bucket of water in which they had to swim.

Other rats were placed in shallow water, where swimming was not necessary. Subsequent to this procedure, the rats were again tasked with navigating the maze. Results showed that the rats that had undergone the stressful swim showed better memory for which way to turn in the T-maze than those placed in shallow water.

To test the validity of the findings—that the memory for navigating the maze was enhanced by the stressful swim and not other forces—researchers conducted a series of additional experiments.

These procedures ruled out that learning the maze itself was a source of stress and showed a clear link between the stress induced by the swim and changes in the memories of navigating the maze, even though the changed memories were unrelated to the stressful experience.

The results show that stress can reactivate unrelated memories, leading to the theory that, in humans, traumatic stress might reactivate non-traumatic memories and link them to the traumatic memory, thereby facilitating the pathological effects seen in post-traumatic stress disorder and other conditions.

Researchers from the Czech Republic’s Academy of Sciences; State University of New York Downstate Medical Center, and Rockefeller University contributed to the study.

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