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(https://directorsblog.nih.gov/2024/12/05/study-suggests-new-experiences-can-refresh-memories-of-past-events-with-implications-for-understanding-ptsd/) Study Suggests New Experiences Can Refresh Memories of Past Events, with Implications for Understanding PTSD
Dec 5th 2024, 09:00

New research in mice suggests a memory of a recent negative event can be linked in the brain to a memory of an earlier, neutral event. Credit: Donny Bliss/NIH, Adobe Stock

Your memories of life experiences are encoded in collections of neurons in the brain that were active at the time the event took place. Later, those same patterns of neural activity are replayed in your mind to help stabilize your memories of past events. But new research suggests those memories aren’t fixed. An NIH-supported study in male mice reveals how an older memory can be “refreshed” and altered by association with newer events.

The findings, reported in (https://www.nature.com/articles/s41586-024-08168-4) Nature, show that a memory of a recent negative event can become linked to the memory of a neutral event that took place days earlier, changing the way it’s remembered. This provides important insight into what we know about how the brain updates and reorganizes memories based on new information. These findings could also have implications for our understanding of neurobiological processes that might occur in the brain in memory-related mental health conditions like (https://www.nimh.nih.gov/health/topics/post-traumatic-stress-disorder-ptsd) post-traumatic stress disorder (PTSD), when people feel stress or fear even in situations that present no danger.

The research team, led by (https://www.denisecailab.com/denise) Denise Cai at the Icahn School of Medicine at Mount Sinai in New York City, wanted to learn more about how new events and associated memories could influence older memories in the hippocampus, a brain region that plays a key role in learning and memory. To explore this, the researchers designed behavioral experiments with mice to track behavior and brain activity as the mice learned from new experiences, rested after each experience, and then recalled memories in the following days.

The researchers found that as the mice rested, each memory was consolidated and stabilized through replaying the experience in their brains. The study team also found that after a negative experience (in this case, a foot shock in a specific environment), the measures of brain activity suggested that the mice replayed the memory of that event along with a memory from a neutral experience that they had recorded days earlier. The researchers suggest that the brain appeared to be searching for potentially related events it could link together to update and integrate the memories. As further evidence for this, the mice subsequently responded more fearfully to the previously neutral environment.

While there is evidence for the importance of sleep for memory storage, the researchers in this study found that the linking of negative and neutral memories took place while the mice were awake and at ease. The findings also suggest that recent memories of bad experiences are more likely than memories of good experiences to become linked with memories from the past.

Although these findings were obtained in a mouse model, according to the researchers, the study results suggest that our brains may integrate memories to form a cohesive understanding of real-world experiences in ways that offer stability and flexibility. These insights suggest that memories of the past are constantly updated and refreshed by new experiences in ways that may help us function in a world marked by constant change.

The findings also suggest that negative experiences can lead us to fear seemingly unrelated places or events in ways that are detrimental. This may help to explain why for people with PTSD, exposure therapy—in which people work to overcome fears through gradual exposures to them in a safe environment—can stop being effective. The hope is that findings like these might shed light on potential new ways to treat PTSD and related disorders.

Reference:

Zaki Y, et al. (https://www.nature.com/articles/s41586-024-08168-4) Aversive experience drives offline ensemble reactivation to link memories across days. Nature. DOI: 10.1038/s41586-024-08168-4 (2024).

NIH Support: National Institute of Mental Health, National Institute of Neurological Disorders and Stroke, National Institute on Aging, National Institute on Drug Abuse

Forwarded by:
Michael Reeder LCPC
Baltimore, MD

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