Some brains seem to defy Alzheimer’s. Even when the disease’s telltale plaques and tangles are present, certain individuals remain mentally sharp well into old age. This phenomenon, known as cognitive resilience, is one of the most intriguing puzzles in neuroscience today.
At the Netherlands Institute for Neuroscience, researchers led by neuroscientist Evgenia Salta have uncovered new clues. Their work suggests that resilience may depend not on the sheer number of brain cells, but on how a special class of cells, called immature neurons, respond to damage.
For decades, neuroscientists have debated whether the adult human brain retains any meaningful population of “immature” neurons, youthful-looking cells tucked inside the hippocampus.
In rodents, these cells have been shown to play active roles in memory and even in buffering against Alzheimer’s disease. But whether humans continue to generate new brain cells in adulthood has been hotly debated, and if so, what do they do?
A new study, published in the journal Cell Stem Cell, has uncovered evidence that could shed some light on the topic. Using single-nucleus RNA sequencing of hippocampal samples from healthy aged donors, Alzheimer’s patients, and individuals resilient to dementia, researchers identified persistent populations of immature neurons across all groups.
The cells carried a kind of “youthful signature,” showing traits of juvenile functions that seemed to fade or break down in Alzheimer’s disease.
Evgenia Salta, the last author, said, “Even at an average age of over 80, we still found these immature neurons in all groups.”
The hippocampus, often called the memory center of the brain, is one of the first areas to fail in Alzheimer’s disease. The very presence of immature neurons, even in adults, implies that they are not remnants of the developmental process but may play an active role in maintaining brain function under stressful conditions.
The team’s experiments and computational analysis showed that these neurons were always present, but their gene activity changed with the disease. The neurons in the more dementia resilient people also held onto many traits of youth, indicating that maintaining this youthful behavior partially shielded their brains from dementia. But in patients with Alzheimer’s, those same characteristics had diminished, indicating a loss of this possible form of protection.
The biggest surprise was that the resilient group didn’t have far more of these cells than the Alzheimer’s patients. The difference wasn’t in the number of immature neurons, but in how they behaved.
In resilient individuals, these cells don’t just sit idle; they activate survival programs that help them withstand damage, while dialing down signals of inflammation and cell death. That means the story isn’t only about replacing lost neurons.
Instead, these immature cells may act as caretakers, nourishing the surrounding tissue and keeping the brain youthful, like fertilizer holding a fragile garden together.
This shifts the focus: instead of asking if adult neurogenesis stops, the main question is how those cells tip the balance toward supporting resilience or toward disease.
The implications are profound. Potential therapies targeting the preservation or recapitulation of juvenile traits in these cell types might be beneficial if they help restore equilibrium in the aging hippocampus. This kind of strategy may open up novel avenues for the prevention of cognitive decline generally or for protecting against Alzheimer’s-related vulnerability/resilience.
Salta states, “Cognitive resilience is extremely exciting. If we understand what protects these brains, it could eventually lead to new therapeutic strategies. For now, the message is clear: the aging brain may be more adaptable and more complex than we once thought.”
This research was published in Cell Stem Cell.
Fact-checked by Mike McRae
