Despite some debates, it is generally accepted that the human hippocampus generates new neurons even in adulthood. Yet, research led by Dr. Arturo Alvarez-Buylla and his team from University of California, San Francisco discovered evidence that neurogenesis in the human hippocampus drops drastically as age progresses.

Neurons are generated from the subgranular zone of the dentate gyrus. Dr. Alvarez-Buylla’s team analyzed 59 post–mortem and post–operative hippocampus samples that ranged from infancy to adulthood. The team’s data showed that at 14 gestational weeks of infancy, the fetal dentate gyrus and neural progenitors were proliferate in the dentate neuroepithelium. Meanwhile, in the 22nd gestational week, the proliferation level of the neural progenitors decreased. In the samples of children from seven to 13 years old, the number of newly generated neurons decreased further. The concluding evidence for the team’s proposition was that no new neurons were found in a 17-year-old’s hippocampus. Hence, the team concluded that production of new neurons in adulthood is extremely rare as neurogenesis decreased with age.