A new rodent study shows that newborn neurons destabilize established connections among existing brain cells in the hippocampus, a part of the brain involved in learning and memory. Clearing old memories from the hippocampus makes way for new learning, researchers from Japan suggest in the November 13 Cell.
Other researchers had proposed the idea that neurogenesis, the birth of new neurons, could disrupt existing memories, but the Cell paper is the first to show evidence supporting the idea, says Paul Frankland, a neuroscientist at the Hospital for Sick Children in Toronto.
Scientists have known that memories first form in the hippocampus and are later transferred to long-term storage in other parts of the brain. For some amount of time the memory resides both in the hippocampus and elsewhere in the brain. What’s not been known is how, after a few months or years, the memory is gradually cleared from the hippocampus.
Researchers have also debated the role of neurogenesis in learning and memory. The hippocampus is one of only two places in the adult brain where scientists know that new neurons form. On the basis of previous studies, many researchers think new neurons stabilize memory circuits or are somehow otherwise necessary to form new memories.
The new study suggests the opposite: Newborn neurons weaken or disrupt connections that encode old memories in the hippocampus.