Human hippocampal neurogenesis drops sharply in children to undetectable levels in adults.
Level 4 - case-series / case-control
Cross-sectional post-mortem and surgical tissue case series.
PubMed 29513649 · doi:10.1038/nature25975
What was done
The authors analyzed human hippocampal dentate gyrus tissue across fetal development, infancy, childhood (including samples at ages 7 and 13), and adulthood (ages 18–77 years; n = 17 post-mortem control samples and n = 12 surgical resection samples from patients with epilepsy) to assess progenitor cell populations, proliferating progenitors, and young neurons. Hippocampal tissue from rhesus macaques (Macaca mulatta) was also examined across early postnatal and juvenile stages.
What was found
A defined progenitor cell population did not coalesce in the subgranular zone during human fetal or postnatal development. Proliferating progenitors and young neurons in the dentate gyrus dropped sharply during the first year of life, with only a few isolated young neurons observed by 7 and 13 years of age. In adult humans (ages 18–77, n = 29 total across control and epilepsy tissue), young neurons were not detected. Macaque hippocampal neurogenesis similarly diminished during juvenile development. Exact numeric cell counts were not reported in the abstract.
Why it matters
This study directly challenges the view that adult humans regularly generate new hippocampal neurons, suggesting neurogenesis drops sharply in early childhood and is undetectable or extremely rare in adults.
Limits
The total sample size for fetal, infant, and pediatric human specimens, as well as the macaque cohort, is not stated in the abstract. Adult tissue was restricted to post-mortem controls and surgical resections from epilepsy patients, which may introduce tissue preservation and pathology confounders.