MIT researchers have discovered that the adult mouse brain contains millions of silent synapses, located on tiny structures called filopodia. Credit: Dimitra Vardalaki and Mark Harnett
Key Points:
- Neuroscientists discover the adult brian contains millions of “silent synapses."
- This process allows the brain to create new memories without overwriting the important older memories.
- Researchers hope to study how age or neurodegenerative disease affect the number or function of these synapses.
MIT neuroscientists have discovered that the adult brain contains millions of “silent synapses”—immature connections between neurons that remain inactive until they’re needed to help form new memories.
Previously, silent synapses were believed to exist only during early development, when they help the brain learn new information it’s exposed to early in life. However, the new MIT study published in Nature revealed that in adult mice, about 30 percent of all synapses in the brain’s cortex are silent.
The existence of these silent synapses may help to explain how the adult brain is able to continually form new memories and learn new things without having to modify existing memories.
“These silent synapses are looking for new connections, and when important new information is presented, connections between the relevant neurons are strengthened. This lets the brain create new memories without overwriting the important memories stored in mature synapses, which are harder to change,” says Dimitra Vardalaki, an MIT graduate student and the lead author of the new study.
When scientists first discovered silent synapses decades ago, they were seen primarily in the brains of young mice and other animals, but then disappeared as they matured. However, some neuroscientists have proposed that silent synapses may persist into adulthood.
As part of the new MIT team study, researchers tried to measure neurotransmitter receptors in different dendritic branches. Using a technique called eMAP, researchers could physically expand a tissue sample and then label specific proteins in the sample, making it possible to obtain super-high-resolution images.
While they were doing that imaging, they made a surprising discovery - filopodia were everywhere.
Researchers are now studying silent synapses in human brain tissue to see whether the number or function of these synapses are affected by factors such as aging or neurodegenerative disease.