Neurogenesis interferes with past learning in infant and adult mice.
For anyone fighting to save old memories, a fresh crop of brain cells may be the last thing they need. Research published today in Sciencesuggests that newly formed neurons in the hippocampus — an area of the brain involved in memory formation — could dislodge previously learned information1. The work may provide clues as to why childhood memories are so difficult to recall.
“The finding was very surprising to us initially. Most people think new neurons mean better memory,” says Sheena Josselyn, a neuroscientist who led the study together with her husband Paul Frankland at the Hospital for Sick Children in Toronto, Canada.
Humans, mice and several other mammals grow new neurons in the hippocampus throughout their lives — rapidly at first, but more and more slowly with age. Researchers have previously shown that boosting neural proliferation before learning can enhance memory formation in adult mice2, 3. But the latest study shows that after information is learned, neuron growth can degrade those memories.
Although seemingly counterintuitive, the disruptive role of these neurons makes some sense, says Josselyn. She notes that some theoretical models have predicted such an effect4. “More neurons increase the capacity to learn new memories in the future,” she says. “But memory is based on a circuit, so if you add to this circuit, it makes sense that it would disrupt it.” Newly added neurons could have a useful role in clearing old memories and making way for new ones, says Josselyn.