MIT: Silent synapses ‘lets the brain create new memories without overwriting the important memories stored in mature synapses’

A new study published in the journal Nature is shedding light on how the adult brain is able to form new memories and absorb new information through “silent synapses” or inactive neuronal connections.

“These silent synapses are looking for new connections, and when important new information is presented, connections between the relevant neurons are strengthened,” said Dimitra Vardalaki, an MIT graduate student and the lead author of the study, according to MIT News. “This lets the brain create new memories without overwriting the important memories stored in mature synapses, which are harder to change.”

MIT News reports the discovery by MIT neuroscientists is surprising as silent synapses were previously believed to only be present early on in a person’s development when the brain is acquiring large amounts of new information. The study found about 30% of all synapses in the cortex of the brain of adult mice are silent.

When silent synapses were first discovered many years ago, scientists primarily saw them in the brains of young mice and other animals. The synapses were always believed to go away by the time mice were 12 days of age, which is equivalent to the first months of a human’s life.

In animal models of addiction, evidence has supported neuroscientists, who have suggested the connections may persist into adulthood and contribute to new memories being formed. Theoretical research puts forward the idea of neurons having plasticity in order for the brain to learn and retain new information.

Findings from the MIT study come following a previous study conducted by Mark Harnett, an associate professor of brain and cognitive sciences and a member of MIT’s McGovern Institute for Brain Research. That previous study used the eMAP technique to measure neurotransmitter receptors in different dendritic branches to see how synaptic input is processed.

“The first thing we saw, which was super bizarre and we didn’t expect, was that there were filopodia everywhere,” Harnett said, according to MIT News.

The new study aimed to look for filopodia, thin membrane protrusions that extend from dendrites, in other parts of the adult brain and determine whether the filopodia might be silent synapses.