One of the most fundamental and intriguing abilities of our brain, is the recording and preserving of memories which allow us to recall our past experiences.
For the last four decades, neuroscientists have been trying to find out more about the biological mechanisms which underlie how we store the information that our brain receives on a daily basis. Now researchers from the Faculty of Medicine of the University of Geneva have been able to demonstrate how the brain is able to regulate the size of the neuronal groups that organise the memories. They’ve also shown that it’s possible to target the neurons within the hippocampus to inhibit or resurface a memory.
The traces that memories leave in our brains are made up of a set of cells, called engram, which are located in the hippocampus. As the brain encodes memories, the neurons within the engram create a neural network. In order to embed a particular memory in the brain, the correct number of neurons need to be activated; too few and the memory won’t be made, too many and it may cause the information to become compromised.
Researchers were able to stimulate particular neurons within the brain of the mice
To understand more about this process, the researchers looked at the mechanisms that control the recruitment of neurons into the engram. They did this by presenting mice with a novel situation so that they would create a memory of what had happened. They then repeated this several times. Using optogenetics, the researchers were able to stimulate particular neurons within the brain of the mice. This forced the mice to use more or less neurons as they created the memory.
This technique enabled the researchers to observe that the cells that are mobilised into the engram also trigger inhibitory cells which prevent activation of the neurons in neighbouring cells. Through the identification of this mechanism, the team learned how the mobilised neurons were able to control the size of the engram, and thus control the stability of the memory. They found that more significant engrams led to better preserved memories, however if the engram grew beyond a certain size, the memory was compromised. Thus, the scientists were able to both artificially reinforce a memory, and also remove it completely.
Now that the team understands the basic mechanism of how the memories are created, they plan to learn more about the function of memory, and whether certain cells create certain kinds of memories.
This latest study was published in a recent edition of the online journal Neuron.
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