For the first time, researchers at Mount Sinai Health System have identified a neural mechanism that enables the integration of memories, a process that spans both time and personal experiences. Published in the journal ‘Nature’, this study reveals how memories, stored in neuronal ensembles in the brain, are constantly updating and reorganizing with relevant information.
This discovery marks an important advance in understanding how our memories remain current and adapt to new information, which could be key to better understanding adaptive memory processes, such as causal inferences, as well as non-adaptive processes, such as cognitive disorder. post-traumatic stress (PTSD).
“It has long been believed that memories are formed in initial learning and remain stable in neural ensembles over time, allowing us to remember specific experiences,” says Denise Cai, Ph.D. in Neuroscience and associate professor at the Icahn School of Medicine at Mount Sinai, and lead author of the study.
‘Our work with mouse models shows that this theory is not entirely correct, as it does not explain how the brain can store memories and, at the same time, update them with new and relevant information. This combination of Stability and flexibility in neuronal ensembles is essential so we can make predictions and make decisions in an ever-changing world.”
The Mount Sinai team studied how memories are dynamically updated when new information is received, a topic that remains a challenge for neuroscience.
neural connection
For their research, the team recorded neural activity and behavior in the hippocampus of adult mice as they acquired new experiences, rested after each one (in “offline” periods), and recalled past experiences on subsequent days. The researchers observed that, after each event, the brain consolidates and stabilizes the memory by repeating the experience.
In the case of a negative experience, the brain not only relived the recent event, but also events that occurred days earlier, suggesting that it seeks to integrate related memories over time.
In mice that experienced a highly adverse event (such as receiving an electric shock in a specific environment), these negative experiences were observed to reactivate not only the recent memory, but also a “neutral” memory from previous days (a safe environment where no there were downloads).
“We discovered that when mice rested after a negative experience, they simultaneously reactivated the neuronal ensemble of that experience and that of the past neutral memory, thus integrating both memories,” explains Dr. Cai. «We call this phenomenon co-reactivation of neural ensembles and we now know that it facilitates the long-term binding of memories in the brain.
Contrary to previous studies highlighting the benefits of sleep for memory storage, the researchers found that memory binding occurred more frequently when the mice were awake. This finding raises interesting questions about the different roles that wakefulness and sleep play in memory processes.
Furthermore, the study showed that negative experiences tend to be linked more to past memories in a “retrospective” than “prospective” manner, and that more intense negative events are more likely to drive this retrospective linkage of memories.
“By discovering a complex neural mechanism that facilitates memory integration, we have taken a significant step towards understanding memory in the real world, where our memories are constantly updated and remodeled with new experiences, allowing us to function in a dynamic world, » concludes Dr. Cai.
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