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The brain stores at least three copies of each memory 

New research in mice suggests that the brain creates multiple copies of memories, allowing it to regulate their change over time

New research suggests that the brain creates at least three copies of each memory. This also includes those encoded by early-formed neurons, which appear purple in a microscope cross-section of a mouse hippocampus. (Image credit: Biozentrum, University of Basel)
New research suggests that the brain creates at least three copies of each memory. This also includes those encoded by early-formed neurons, which appear purple in a microscope cross-section of a mouse hippocampus. (Image credit: Biozentrum, University of Basel) 

Memories develop throughout our lives, changing as we learn and experience new things and as we recall memories again and again. Then, memories deteriorate as we get older.

Previously, scientists thought that this flexibility was the result of changes in the brain cells that originally encoded the memory, and they believed that these cells store only one copy of each memory in the brain. However, new research suggests that this may not be true.

The scientists discovered that in rodents, the brain stores at least three copies of a particular memory, and encodes it in several places in the organ.

These copies are encoded by different groups of neurons in the hippocampus, an area of ​​the brain critical for learning and memory. The copies differ in terms of when they were created, how long they last, and how changeable they are over time.

In the new study, published August 16 in the journal Science, the scientists showed that when the mice encode new memories, they first create what are called early-born neurons. These neurons are responsible for storing a long-term copy of the memory, which is initially weak but becomes stronger over time.

Next come intermediate neurons, which are more stable than the first neurons, followed by late-formed neurons that initially encode very strong copies of a memory. However, this strength weakens over time.

The researchers uncovered these findings by examining the activity of different groups of neurons in the hippocampus after the mice completed different memory tasks. These tasks involved learning to avoid harmful situations, such as receiving an electric shock to their legs, before facing the same task again later.

The way these three groups of neurons work at different times may help explain how the brain regulates memories over time, the study authors suggested. However, it's still unclear exactly how these neurons communicate with each other to facilitate this, study co-author Flavio Donato, an associate professor of neurobiology at the University of Basel in Switzerland, told Live Science.

The team found that the memories stored by late-formed neurons were more plastic, or flexible, than those of early-formed neurons. This suggests that early in memory formation—when early-born neurons dominate—stored information remains fairly stable over time, while later stored memories are more easily distorted by new information.

If the same phenomenon occurs in humans, this finding could one day lead to the development of new treatments for specific disorders, Donato said. For example, in post-traumatic stress disorder (PTSD), people experience intrusive memories, that is, unwanted and disturbing memories of a traumatic event. It may be possible to design a drug that preferentially activates the late-generated neurons, which are more plastic and therefore more responsive to psychotherapy, he said.

In a story related to memory loss due to dementia, for example, a different type of drug can stimulate the activity of the early-formed neurons, whose data is stored more rigidly. More broadly, such treatments would take advantage of the properties of memory by choosing which type of neuron would be used to encode it in the brain, Donato explained.

"I feel that now we have enough data in a way that may allow us to push in a more or less plastic direction, in order to preserve it or actually rewrite it," Donato said.

for the scientific article

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