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Humans can make new brain cells up to the age of 90, but the production of new neurons affects those with Alzheimer's disease, even when the disease has recently settled, scientists have discovered.
The findings could help doctors diagnose early-stage Alzheimer's disease and identify those most at risk for exercise and other interventions that may stimulate the production of new brain cells.
This work is the latest in a topic that has divided neuroscientists for decades. Some claim that humans have all their brain cell quota in adulthood, while others claim that fresh neurons continue to age.
In research that can help solve the problem, Spanish scientists performed a battery of tests on brain tissue donated by 13 people aged 43 to 87 years. All were in good neurological health before their death.
María Llorens-Martin, neuroscientist at the Autonomous University of Madrid and senior scientist of the study, discovered that even though the healthy brain contained neurons of the newborn, their numbers gradually decreased with the # 39; age. Between 40 and 70 years, the number of fresh neurons detected in the part of the brain studied fell from about 40,000 to 30,000 per cubic millimeter.
The new cells are born in the part of the brain called dentate gyrus. It is a part of the seahorse that plays a central role in learning, memory, mood and emotions. The gradual reduction in the number of new brain cells seemed to go hand in hand with the cognitive decline associated with aging. This suggests that at the average age, about 300 fewer neurons per cubic millimeter are made in the dentate gyrus each year.
The study, published in the journal Nature Medicine, suggests that scientists do not agree to say whether an adult brain makes new neurons is due to the fact that different tests and treatments of tissues give different results. "In the same brain, we can detect many immature neurons or no immature neurons depending on tissue processing," said Llorens-Martin.
After studying healthy brain tissue, the scientists then examined the brains of people diagnosed with Alzheimer's disease prior to death. This time, the researchers analyzed the brain tissue of 45 patients aged 52 to 97 years. All had fresh brain cells in the dentate gyrus, including the oldest 97-year-old, the oldest person in whom "neurogenesis" was still observed.
However, while patients with Alzheimer's disease showed signs of new brain cell formation, there were clear differences with healthy brains. Even at the very beginning of the disease, their brains accounted for only half to three-quarters of the number of fresh neurons compared to healthy ones.
"This is very important for the field of Alzheimer's disease because the number of cells you detect in healthy subjects is always greater than the number detected in patients with Alzheimer's disease, regardless of their age, "said Llorens-Martin. "This suggests that an independent mechanism, different from physiological aging, could result in this decreasing number of new neurons." She explained that research was only possible thanks to the generosity of people who donated their brains to science.
She added that brain scans may one day be able to detect newly formed brain cells and thus diagnose Alzheimer's disease at an early stage. Based on rodent studies, those most at risk of contracting the disease could potentially benefit from exercise, socialization and cognitive stimulation.
Sandrine Thuret, head of the Neurogenesis and Mental Health Laboratory at King's College London, said the paper was "extremely timely" and provided "further strong evidence that neurogenesis is occurring in the adult human hippocampus."
Thuret said that Alzheimer's would not be cured by restoring neurogenesis once it had already been diagnosed and diagnosed. But she added that it was possible to use neurogenesis as a marker of Alzheimer's disease before implantation. "If you could just prevent or delay the onset of cognitive symptoms of Alzheimer's disease for a few years while maintaining neurogenesis, that would be fantastic," she said.
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