Brain Found to Store Three Copies of Every Memory

Like a computer system with built-in redundancies, one study found that brains use three different sets of neurons to store a single memory. A finding that could one day help smooth painful memories in people who have experienced trauma.

Researchers at the Biozentrum of the University of Basel were able to monitor the brains of mice to see what happens when a new memory is formed. What they found was that rodent brains fire three different sets of neurons to record the memory. The first are known as early-born neurons, which develop earliest as the fetus grows. At the other end of the spectrum are late-born neurons, which appear later in embryonic development. In between, there are neurons that form somewhere in the middle of growth in the womb.

The imaging study revealed that when new memories are stored in prematurely born neurons, they are initially harder to recall, but become stronger as time goes on.

On the other hand, the copy of the memory stored in the late-born neurons was initially very strong, but weakened over time until it became inaccessible to the brain. In the middle, the memory copy showed a higher degree of stability than in any of the other groups of neurons.

This cross-section of a mouse's hippocampus shows the early-born neurons responsible for creating a long-term copy of a memory in magenta
This cross-section of a mouse's hippocampus shows the early-born neurons responsible for creating a long-term copy of a memory in magenta

University of Basel, Biozentrum

“The challenge the brain faces with memory is impressive,” says Flavio Donato, head of the research group at the Biozentrum. “On the one hand, it needs to remember what happened in the past to help us understand the world we live in. On the other hand, it needs to adapt to the changes that are happening around us, and our memory needs to adapt as well to help us make appropriate choices for our future.”

With their new understanding, the researchers were able to look deeper into how memories are formed and accessed. It’s important to note that, although the study was conducted in mice, their brains are often used in neuroscience as a proxy for ours because they have 75 different cell types in their cortex, the same as humans. However, the results at this point are mouse-specific.

However, the researchers believe their work could have implications for treating people who have been harmed by a traumatic event. That's because they say their work shows how memories can be altered in the brain. For example, if a memory is fresh, meaning that late-born neurons have been activated, it can still be altered before it's passed on to middle- and early-born neurons for storage. But once the late-born neurons are activated and the memory is stored there, it becomes increasingly difficult to alter. Essentially, the longer a memory has been stored in the brain, the harder it is to alter.

“The extent to which memories are dynamically stored in the brain is evidence of the brain's plasticity, which underlies its enormous memory capacity,” says Vilde Kveim, lead author of the study.

Understanding this flexibility, as done through the work conducted by Kveim and his team, could one day help scientists understand how people can access memories they thought were lost forever or silence painful memories that pathologically interfere with daily life.

The team's work was published in the journal Science.

Source: University of Basel

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