PARIS – Around the age of 13, the human brain region that hosts memory and learning appears to stop producing nerve cells, said a study Wednesday.
The finding challenges a widely held view that the hippocampus continues to generate neurons, which transmit information through chemical and electrical signals, well into adulthood in humans, as in other mammals.
Some research had suggested that hundreds of neurons are created in the human hippocampus every day, and it was thought that finding ways to boost such neurogenesis may help tackle age-related brain degeneration.
Looking at brain samples from 59 adults and children, however, “we found no evidence of young neurons or the dividing progenitors of new neurons” in the hippocampi of people older than 18, said study co-author Arturo Alvarez-Buylla of the University of California in San Francisco.
They did find some in children between birth and 1 year old, “and a few at 7 and 13 years of age,” he said.
Published in the scientific journal Nature, the study “shows that the human hippocampus is largely generated during fetal brain development,” the team said.
They did find some newly created neurons in different bits of the brain called ventricles, but said other regions have yet to be explored to determine whether or not neurogenesis happens there.
In a comment carried by Nature, neuroscientist Jason Snyder from the University of British Columbia described the study results as “sobering.”
“These findings are certain to stir up controversy,” he said, and underlined that they would have to be confirmed by other researchers.
There had been a “general consensus that the hippocampus is one region in which adult neurogenesis exists in humans as it does in animals,” he wrote.
“This is based on several studies.”
But the authors of the latest paper said previous research may have misreported the detection of new hippocampal neurons because the protein that is used to trace them in animals does not work the same way in humans.
The hippocampus has also been linked to mood, stress and some neurological diseases in humans.
Adult neurogenesis has been observed in the hippocampi of rodents and monkeys. But it is known not to occur in cetaceans — dolphins, porpoises and whales.