How memory formation is triggered by stem cells

Researchers at the RIKEN-MIT Center for Neural Circuit Genetics have discovered an answer to the long-standing mystery of how brain cells can remember new memories while also maintaining older ones.
They found that specific neurons in a brain region called the dentate gyrus serve distinct roles in memory formation depending on whether the neural stem cells that produced them were of old or young.
The study links the cellular basis of memory formation to the birth of new neurons, a finding that could unlock a new class of drug targets to treat memory disorders. The findings also suggest that an imbalance between young and old neurons in the brain could disrupt normal memory formation during post-traumatic stress disorder (PTSD) and aging.
The researchers tested mice in two types of memory processes: pattern separation (the process by which the brain distinguishes differences between similar events) and pattern completion (recalling detailed content of memories based on limited clues). Pattern separation forms distinct new memories based on differences between experiences; pattern completion retrieves memories by detecting similarities.
The researchers found that young neurons are required for pattern separation, while old neurons are required for pattern completion.
Individuals with brain injury or trauma (deficient in old neurons) may be unable to recall people they see every day. Others with PTSD are unable to forget terrible events (deficient in young neurons).