Immature Brain Cells May Hold a Clue to Why Some People Resist Alzheimer's Symptoms

Roughly 30 percent of older adults whose brains develop Alzheimer's disease never experience its symptoms. That figure comes from Evgenia Salta, senior author of a new study from the Netherlands Institute for Neuroscience, and she is plain about what it leaves unanswered: nobody really knows why. She calls it a big mystery, and a very important one.

Salta and her colleagues went looking for a clue in donated human brain tissue supplied by the Netherlands Brain Bank, which collects and preserves brain samples for research. They compared three groups: people with no detectable brain pathology, patients who developed Alzheimer's dementia, and people whose brains showed Alzheimer's pathology but who stayed cognitively resilient, meaning their memory and thinking held up despite the damage.

They concentrated on a small region within the brain's memory center, one of the few places where new neurons are thought to arise. The cells they wanted are extremely rare, so the team had to develop new ways to find them, zooming in on the exact spot where they expected them to be. They also built new approaches to analyzing the data, which let them identify the cells without leaning heavily on assumptions drawn from animal studies.

The search turned up immature neurons in all three groups. These cells resemble neurons that have not fully matured. "Even at an average age of over 80, we still found these immature neurons in all groups," Salta says. Whether the adult human brain makes new neurons has been debated for decades, though adult neurogenesis is established in several animal species. Finding immature neurons does not prove they were recently formed.

The researchers had expected resilient people to carry substantially more of these cells, on the logic that more replacements might explain why some brains withstand the disease. The difference in numbers was far smaller than anticipated. That pointed them toward a different question: not how many immature neurons a brain holds, but how those cells behave under attack.

Here the groups diverged. In resilient individuals, the cells appeared to activate programs tied to survival and coping with damage, and they showed lower signals related to inflammation and cell death. Persistent inflammation in the brain can injure tissue and interfere with communication between neurons, and cell death steadily erodes the networks behind memory and thinking.

Salta suggests the cells' role may go beyond self-protection. "It might not be (only) about replacing lost neurons," she says. They could support the surrounding tissue and help the brain stay functional and "youthful," acting as a sort of fertilizer in a garden that has started falling apart.

She is careful about the limits. The protective role is inferred from patterns in tissue, not demonstrated by direct experiments. "We assume the cells' function based on the data, but we cannot confirm it in this type of study," she says. The findings do not show that new neurons are continuously produced in older people, nor that these cells prevent dementia. Other mechanisms almost certainly contribute. "This is one piece of a very large puzzle," Salta says.

Next, the team plans to study how immature neurons communicate with neighboring brain cells, which may show whether they actively drive resilience. The work reflects a wider shift in Alzheimer's research, from the processes that damage the brain, such as abnormal protein buildup and neuron loss, toward asking why some brains keep working anyway. Salta describes a decision point along the trajectory of aging, where some people stay stable and others develop dementia. Treatments remain a distant prospect, but she says that understanding what protects these brains could eventually lead to new therapeutic strategies.