MIT neuroscientists have uncovered a surprising feature of the adult brain. It contains millions of "silent synapses," which are immature connections between neurons that remain inactive until they are needed to help form new memories. For many years, scientists believed these silent synapses existed only during early development, when the brain is rapidly learning about the world. But the MIT team found that in adult mice, roughly 30 percent of synapses in the brain's cortex are still silent. This suggests the adult brain holds a large reserve of unused connections that can be activated when new information arrives. Researchers say this hidden pool of synapses may explain how the brain continues to learn throughout life without disrupting existing memories. "These silent synapses are looking for new connections, and when important new information is presented, connections between the relevant neurons are strengthened.…