A study published in Nature (2018) reveals that human hippocampal neurogenesis sharply declines during childhood and becomes undetectable in adults. The research, led by a team of scientists from multiple institutions, examined postmortem and intraoperative samples of the human hippocampus to investigate the presence of progenitor cells and young neurons from fetal to adulthood stages. The findings indicate that a defined population of progenitor cells does not coalesce in the subgranular zone (SGZ) during human fetal or postnatal development. Proliferating progenitors and young neurons in the DG sharply decline in the first year of life, with only a few isolated young neurons observed by 7 and 13 years of age. In adult patients, young neurons were not detected in the DG. In monkeys, a proliferative SGZ was present in early postnatal life but diminished during juvenile development as neurogenesis declined. The study concludes that the recruitment of young neurons to the primate hippocampus declines rapidly during the first years of life, and that DG neurogenesis does not continue, or is extremely rare, in the adult human. The early decline in hippocampal neurogenesis raises questions about how the function of the dentate gyrus differs between humans and other species in which adult hippocampal neurogenesis is preserved. The study used a variety of techniques, including immunohistochemistry, electron microscopy, and RNA in situ hybridization, to analyze the presence of progenitor cells and young neurons in the DG. The results indicate that the human DG does not contain a proliferative SGZ, and that the number of proliferating cells expressing progenitor/stem cell markers becomes largely depleted from the hilus by 7 years of age. The study also found that young neurons in the DG are rare in adults, with only a few isolated cells observed. The findings challenge the notion that robust adult neurogenesis continues in the human hippocampus and suggest that the human DG does not generate new neurons in adulthood. The study highlights the importance of understanding the limitations of adult neurogenesis in the human and other species to interpret findings from animal models.A study published in Nature (2018) reveals that human hippocampal neurogenesis sharply declines during childhood and becomes undetectable in adults. The research, led by a team of scientists from multiple institutions, examined postmortem and intraoperative samples of the human hippocampus to investigate the presence of progenitor cells and young neurons from fetal to adulthood stages. The findings indicate that a defined population of progenitor cells does not coalesce in the subgranular zone (SGZ) during human fetal or postnatal development. Proliferating progenitors and young neurons in the DG sharply decline in the first year of life, with only a few isolated young neurons observed by 7 and 13 years of age. In adult patients, young neurons were not detected in the DG. In monkeys, a proliferative SGZ was present in early postnatal life but diminished during juvenile development as neurogenesis declined. The study concludes that the recruitment of young neurons to the primate hippocampus declines rapidly during the first years of life, and that DG neurogenesis does not continue, or is extremely rare, in the adult human. The early decline in hippocampal neurogenesis raises questions about how the function of the dentate gyrus differs between humans and other species in which adult hippocampal neurogenesis is preserved. The study used a variety of techniques, including immunohistochemistry, electron microscopy, and RNA in situ hybridization, to analyze the presence of progenitor cells and young neurons in the DG. The results indicate that the human DG does not contain a proliferative SGZ, and that the number of proliferating cells expressing progenitor/stem cell markers becomes largely depleted from the hilus by 7 years of age. The study also found that young neurons in the DG are rare in adults, with only a few isolated cells observed. The findings challenge the notion that robust adult neurogenesis continues in the human hippocampus and suggest that the human DG does not generate new neurons in adulthood. The study highlights the importance of understanding the limitations of adult neurogenesis in the human and other species to interpret findings from animal models.