Superagers Grow New Brain Neurons Faster Than Their Peers. Alzheimer's Patients Barely Grow Any.
Somewhere in the brains of octogenarians with the memory of people half their age, neurons are still being born. The finding, published in Nature, comes from direct examination of donated human brain tissue - not from animal models or inference from imaging studies - and it adds a concrete biological correlate to a cognitive phenomenon that has been documented but poorly explained.
The researchers, from the University of Illinois Chicago, Northwestern University, and the University of Washington, examined brain samples from five groups: healthy young adults, healthy older adults, older adults with exceptional memory (designated superagers), individuals with mild or early-stage dementia, and those with a confirmed Alzheimer's disease diagnosis. The key measure was adult neurogenesis in the hippocampus - the brain region central to memory formation and one of the few areas where new neurons have been shown to develop throughout life.
What the Tissue Showed
Superagers - octogenarians with memory performance comparable to people in their fifties or sixties - showed the highest rates of new neuron production among the older groups. Healthy older adults without exceptional cognition showed less. Those with early dementia showed further reduction. Alzheimer's patients showed negligible new neuronal growth.
The gradient is striking. It suggests that the capacity for hippocampal neurogenesis is not simply an all-or-nothing phenomenon that declines uniformly with age, but rather that it varies substantially among individuals and tracks with cognitive outcomes in a way that may be meaningful.
"This is a big step forward in understanding how the human brain processes cognition, forms memories and ages. Determining why some brains age more healthily than others can help researchers make therapeutics for healthy aging, cognitive resilience and the prevention of Alzheimer's disease and related dementia," said Orly Lazarov, professor in UIC's College of Medicine and director of the Alzheimer's Disease and Related Dementia Training Program.
A Long-Running Scientific Controversy
Adult neurogenesis in humans has been contested territory for years. After researchers established in the latter half of the 20th century that new neurons develop in the rodent hippocampus throughout life, studies in primates extended the finding to non-human species. But whether the same process occurs in adult humans at meaningful levels has been debated, with some high-profile studies arguing it does not.
The new study, using donated tissue and direct histological methods rather than imaging proxies, adds to the body of evidence supporting human adult neurogenesis and connects it specifically to cognitive performance. The study affirms that neurogenesis occurs in adult humans, and it goes further by demonstrating that the rate differs between cognitive groups in a manner consistent with the hypothesis that new neurons support memory function.
What This Does and Doesn't Establish
Several important caveats apply. The study is cross-sectional, not longitudinal - it compared brains at one point in time rather than tracking individuals as they aged. This means causation cannot be established directly. It is possible that superagers have higher neurogenesis because their memories are better, rather than the other way around. It is also possible that some third factor - genetic, lifestyle, or physiological - independently produces both exceptional cognition and elevated neurogenesis.
The donated tissue samples also represent people who agreed to participate in brain donation programs, which may not perfectly represent the general population. And the number of superager brains available for study is inherently limited - genuine cognitive superagers are rare.
What the study does establish is a correlation strong enough and a gradient clear enough to make neurogenesis rate a serious candidate for investigation as a marker of brain aging. If the relationship holds up in larger samples and longitudinal designs, it opens a line of research into what drives the difference - whether factors like exercise, sleep, stress, or specific genetic variants predict neurogenesis rates - and whether that rate can be influenced.
Alzheimer's researchers have particular interest in the lower end of the gradient. The near-absence of new neuron growth in Alzheimer's brains, if confirmed as a consistent feature rather than an artifact of sample selection, would be relevant for understanding the disease's progressive memory loss and potentially for evaluating interventions.