Stability of a Memory: from forming to fading

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Researchers at Caltech have identified the neural process that makes some memories stable, while others fade very easily. This can also be an implication of the understanding of brain damage and Alzheimer’s disease.

To figure out how memories form, the team developed a test to examine mice’s neural activity as they learn about and remember a new place. In the test, a mouse was placed in a straight enclosure, about 5 feet long with white walls. Unique symbols marked different locations along the walls – for example, a bold plus sign near the right-most end and an angled slash near the centre. Sugar water (a treat for mice) was placed at either end of the track. While the mouse explored. The researchers measured the activity of specific neurons in the mouse hippocampus (the region of the brain where new memories are formed) that are known to encode for places.

Upon studying how memories fade, they decided to withhold the mice from the track for twenty days and observe the results. They found that the mice had the capability of remembering the task quickly due to the encoding of the higher number of neurons. Although some neurons showed different activity, the mouse’s memory of the track was clearly identifiable when analyzing the activity of large groups of neurons.

Through the experiment, they have concluded that neurons firing in synchrony can help in providing redundancy which enables these memories to persist over time. The work was done in the laboratory of Carlos Lois, a research professor of biology, and is described in a paper that appears in the August 23 of the journal Science.

“Imagine you have a long and complicated story to tell. In order to preserve the story, you could tell it to five of your friends and then occasionally get together with all of them to re-tell the story and help each other fill in any gaps that an individual had forgotten. Additionally, each time you re-tell the story, you could bring new friends to learn and therefore help preserve it and strengthen the memory. In an analogous way, your own neurons help each other out to encode memories that will persist over time.”


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