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A new study suggests that the answer to how we store memories lies in the connections between certain brain cells, rather than within the cells themselves.
Researchers from Trinity College Dublin have been scratching their heads to uncover how the brain stores memories.
The team looked at certain forms of learning and believe that the answer lies in the continuous formation of connectivity patterns between specific cells in different regions of the brain.
These cells are known as ‘engrams’, which the researchers define as changes in the brain when information is retained for later use.
“Memory engram cells are groups of brain cells that, activated by specific experiences, change themselves to incorporate and thereby hold information in our brain,” said Dr Clara Ortega-de San Luis, a postdoctoral researcher and lead author of the study.
“Reactivation of these ‘building blocks’ of memories triggers the recall of the specific experiences associated to them. The question is, how do engrams store meaningful information about the world?”
The team – led by Dr Tomás Ryan – wished to learn more about how experiences modify the cells in our brains to form new memories. To do this, they studied a form of learning in which two similar experiences become linked by the nature of their content.
The researchers used genetic techniques to label two different populations of engram cells in the brain for two discrete memories. They then monitored how learning manifested in the formation of new connections between those two populations of cells.
The team used optogenetics to observe these connections. This is a method that lets researchers control brain activity with light.
The researchers claim they identified a certain molecular mechanism, which is linked to a specific protein located in the synapse that is involved in regulating the connectivity between engram cells.
This study suggests that these changes in synaptic connections between engram cells are a likely mechanism for how memories are stored in the brain. Ryan said this runs counter to other theories around memory storage.
“In 21st century neuroscience, many of us like to think memories are being stored in engram cells, or their sub-components,” Ryan said. “This study argues that rather than looking for information within or at cells, we should search for information between cells, and that learning may work by altering the wiring diagram of the brain – less like a computer and more like a developing sculpture.
“In other words, the engram is not in the cell; the cell is in the engram.”
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