The development of new neurons in the brain’s hippocampus decreases as we get older and has stopped completely by adulthood, reports a paper published online this week in Nature.
Neurons are cells that carry electrical impulses. In some mammals, new neurons are created throughout adulthood within the hippocampus - a process that has been linked to memory, mood, stress, exercise and neurological diseases. Previous studies have suggested that in humans, neurons alsocontinue to be formed in the hippocampus during adulthood. Studying this neurogenesis, it had been thought, might improve our understanding of learning processes, emotional disorders and neurodegenerative diseases.
A new study by Arturo Alvarez-Buylla and colleagues, however, suggests that neurogenesis may not continue for as long as has previously been thought. The authors used marker antibodies to reveal neural precursor cells and immature neurons in 59 human brain tissue samples that were taken from subjects of various ages - from fetal to adulthood stages. The authors found that new neurons are produced early in life, but neuron formation rates decrease rapidly as subjects get older. The oldest sample that still contained developing neurons was taken from a 13-year-old subject. The authors propose that previous studies may have misreported the detection of immature neurons, because the proteins used to mark these neurons in animals do not work the same way in humans.
In an accompanying News & Views article, Jason Snyder notes that these results in humans are not inconsistent with similar studies in animals - neurogenesis in rodents also diminished by middle age. He concludes: “If the focus of rodent studies were shifted to identifying the mechanisms by which neurogenesis diminishes over time, and to how neurogenesis can be enhanced to offset pathology caused by age and disease, we just might be able to translate the authors’ sobering findings into discoveries that improve human health.”