Around 30 percent of older adults whose brains accumulate the plaques and tangles of Alzheimer’s disease never develop dementia. They remain cognitively normal despite harboring the same pathology that robs others of memory and identity. This phenomenon, known as cognitive resilience, has been one of the most perplexing mysteries in Alzheimer’s research.
A study published July 3 in Cell Stem Cell by researchers at the Netherlands Institute for Neuroscience provides a new answer. The key, they find, is not that resilient brains produce more new neurons, but that the immature neurons they do possess activate protective programs that help them survive damage and support the surrounding tissue.
“This is one piece of a very large puzzle,” said senior author Evgenia Salta, a group leader at the institute. “There will never be just one factor that explains resilience. But understanding what protects these brains could eventually lead to new therapeutic strategies.”
Zooming in on a rare cell population
The hippocampus, the brain’s memory center, is one of the few regions where new neurons are thought to be generated throughout life, a process called adult neurogenesis. But the newborn neurons are rare, and studying them in human tissue is technically challenging.
The team, led by first author Giorgia Tosoni, developed new analytical methods specifically designed to detect these scarce cells in donated human brain tissue from the Netherlands Brain Bank. They examined three groups of donors: cognitively healthy individuals with no Alzheimer’s pathology, Alzheimer’s patients who had dementia, and resilient individuals who had Alzheimer’s pathology but remained cognitively normal.
“We had to develop new ways to find these cells,” Salta said. “They are extremely rare, so we really zoomed in on the exact spot where we expected them to be.”
The strategy paid off. Immature neurons, young cells that have not yet fully matured, were found in all three groups, even in donors over 80 years old. This alone was notable, as it confirms that the potential for new neuron formation persists into very old age.
Quality over quantity
The critical difference between resilient brains and those that succumbed to dementia was not the number of immature neurons. Resilient individuals did not have dramatically more of them. Instead, the difference was in how the cells behaved.
Transcriptional profiling revealed that immature neurons in resilient brains activated gene programs associated with cell survival and damage coping. They showed lower levels of inflammation and cell death signals compared to immature neurons in Alzheimer’s brains with dementia.
“In resilient individuals, these cells seem to activate programs that help them survive and cope with damage,” Salta said. “We also see lower signals related to inflammation and cell death.”
The interpretation the researchers offer is a shift in thinking about what adult neurogenesis does in the aging brain. Rather than replacing lost neurons, the traditional view, the immature neurons may play a supportive role, maintaining the health of the surrounding hippocampal tissue.
“It might not be only about replacing lost neurons,” Salta said. “It could be that these cells support the surrounding tissue and help the brain stay functional and youthful. They may act as a sort of fertilizer in a garden that has started falling apart.”
A pivot in resilience research
The finding adds a new dimension to the study of cognitive resilience, which has largely focused on genetic factors, lifestyle variables, and the accumulation of protective proteins. The idea that immature neuron activity, and in particular the cells’ survival and stress-response programs rather than their proliferation, contributes to resilience opens a new avenue for therapeutic development.
Instead of trying to stimulate the production of more new neurons, which has proven difficult in the human brain, therapies might aim to protect existing immature neurons and support their survival programs. This is a more tractable goal, as it targets molecular pathways that are already active in the cells.
The researchers caution that they cannot observe these cells in live action, the study is based on post-mortem tissue, which provides a snapshot rather than a dynamic view. Resilience is also almost certainly multifactorial. Genetic background, education, cognitive engagement, cardiovascular health, and many other variables are known to contribute.
“Somewhere along this trajectory, there’s a kind of decision point,” Salta said. “Some people remain stable, others develop dementia. We want to understand what drives that difference.”
The next step is to investigate how immature neurons communicate with other brain cells, astrocytes, microglia, and mature neurons, to exert their protective effects. Understanding those interactions could reveal the specific signals that maintain hippocampal health in the face of Alzheimer’s pathology.
Source: Tosoni G, Ayyildiz D, Snoeck S, et al. Transcriptional profiles of immature neurons in aged human hippocampus track Alzheimer’s pathology and cognitive resilience. Cell Stem Cell (2026). DOI: 10.1016/j.stem.2026.04.002