A new study has revealed how the brain stores memories in multiple neural copies that vary over time, a finding that could revolutionize our understanding of memory and its adaptability throughout life.
The ability to convert experiences into memories allows us to learn from the past and use what we have learned as a model for responding appropriately to new situations. Therefore, as the world around us changes, this memory model cannot simply be a fixed archive of the “good old days” but must be dynamic, changing over time to adapt to new circumstances and help us predict the future and select the best course of action.
How the brain could regulate the dynamics of a memory was a mystery, but now a new study by researchers at the University of Basel has discovered multiple copies of memories. Specifically, it has revealed that the memory of a specific experience is stored in multiple parallel ‘copies’ that are retained for varying periods, modified to some degree, and sometimes deleted over time. The findings have been published in Science.
Professor Flavio Donato’s research group at the Biozentrum of the University of Basel uses mouse models to investigate how memories are stored in the brain and how they change throughout life. His team has found that in the hippocampus, a brain region responsible for learning from experience, a single event is stored in parallel memory copies between at least three different groups of neurons, which arise at different stages during embryonic development.
Flexible memories help us make decisions
Neurons that appear first during development are responsible for the long-term persistence of a memory. Indeed, although their memory copy is initially too weak for the brain to access, it strengthens over time. In humans, too, the brain might only have access to such a memory some time after it has been encoded.
In contrast, the memory copy of the same event created by late-born neurons is very strong at first, but fades over time, so that if one waits long enough, the copy becomes inaccessible to the brain. At some intermediate point, between neurons that emerge between the two extremes during development, a more stable copy can be observed.
Surprisingly, which copy is used might also be related to how easily a memory can be changed or used to create a new one. Memories stored shortly after acquisition by late-born neurons can be modified and rewritten. This means that remembering a situation soon after it has occurred prepares late-born neurons to activate and integrate the information present within the original memory.
“The dynamic way in which memories are stored in the brain is evidence of the brain’s plasticity, which underpins its enormous memory capacity.”
In contrast, recalling the same event after a long time triggers early-born neurons to retrieve its copy, but the associated memory can no longer be easily modified. “The dynamic way in which memories are stored in the brain is evidence of the brain’s plasticity, which underpins its enormous memory capacity,” said first author Vilde Kveim.
“The challenge the brain faces with memory is quite impressive. On the one hand, it must remember what happened in the past to help us understand the world we live in. On the other, it needs to adapt to the changes happening around us, and so must our memories, to help us make appropriate decisions for our future,” adds Flavio Donato.
Researchers have shown that the activation of specific memory copies and their timing could have significant consequences for how we remember, change and use our memories and hope that understanding what drives memories to be encoded and modified in the brain may be useful in the future to help soften those memories that are pathologically intrusive in our daily lives, or recover some that we thought were lost forever.
