Many people’s brains deteriorate as they age, becoming riddled with malfunctioning proteins that result in cell death and the loss of memory. But others remain almost perfectly intact, their thinking as sharp at 80 as it was in their 50s
A paper in the journal Nature provides a new potential explanation for this discrepancy, tapping into a hot debate in neuroscience: whether human brains can grow new neurons in adulthood, a phenomenon called neurogenesis.
The study found that so-called superagers — people 80 and older with the memory of someone 30 years younger — had roughly twice as many new neurons as older adults with normal memory and 2.5 times more than those with Alzheimer’s. Research focused on the hippocampus, the primary birthplace of new neurons.
“This paper shows biological proof that the ageing brain is plastic,” said Tamar Gefen, an associate professor at Northwestern University.
To look for neurogenesis, scientists identified genetic markers for three cell types: neural stem cells, neuroblasts, and immature neurons. “It’s almost like neural stem cells are babies, neuroblasts are teenagers, and immature neurons are almost adults,” said Orly Lazarov, a professor at the University of Illinois at Chicago, who led the research.
The team searched for these cells in the autopsied brains of young adults and four groups of older adults. Each group had signs of all three cell types, but amounts differed dramatically. Superagers had substantially more immature neurons in their hippocampi than other older adults and even young adults. These neurons had unique genetic characteristics that researchers believe made them resilient to aging.
“Superaging happens not only because there’s more of these young cells, but because there is a type of genetic programming” allowing for their preservation, Gefen said.
Bryan Strange, a professor at the Polytechnic University of Madrid, said neurogenesis could explain why the hippocampus in superagers is often much larger. However, he noted superagers have other differences, like greater connectivity between brain regions, that this study doesn’t explain.
The research also uncovered something interesting about the Alzheimer’s group. They had more neural stem cells than other older adults but far fewer neuroblasts and immature neurons.
“If you have normal neurogenesis, you gradually lose the stem cells,” said Hongjun Song, a professor at the University of Pennsylvania. In Alzheimer’s, neurogenesis may be disrupted, leaving stem cells dormant. “If that’s true, that’s really opened up a new direction” to potentially treat Alzheimer’s by reactivating those cells, Song said.
Not everyone is convinced. Shawn Sorrells, an associate professor at the University of Pittsburgh, warned that the study might suffer from methodological flaws and wants the findings validated using other techniques.
While experts agree that children and certain animals generate new neurons, it remains unclear if human adults do. Numerous studies provide evidence on both sides. This latest study won't settle the debate, but it gives scientists new leads. Lazarov is now trying to understand how these special neurons relate to superior memory and if it is possible to capture that activity in a drug.
The New York Times