Editor’s summary

Whether adult neurogenesis occurs in the human hippocampus is one of the most debated issues in neuroscience. Dumitru et al. used a single-cell transcriptomic approach to address this issue in human samples of various ages from birth through adulthood (see the Perspective by Quiniou and Jessberger). Machine learning algorithms helped the authors to identify proliferating neural progenitor cells in the adolescent and adult human hippocampus that resembled progenitor cells found in mouse and pig. The results support the idea that adult neurogenesis occurs in the human hippocampus and add valuable insights of scientific and medical interest. —Mattia Maroso

Still, not everyone in the field agrees that the cells identified in this study are indisputably emerging adult neurons. “When I first heard about this study, I was excited. It’s the sort of approach you would want to use to ID rare subtypes,” Shawn Sorrells, a neuroscientist at the University of Pittsburgh who co-authored the 2018 study with Paredes, tells Popular Science.

But, after a closer look, he was “disappointed by how few cells they found,” and in his view, there’s an alternate potential explanation.

“The most likely conclusion is that the cells they are looking for are rare or nonexistent in most people. The other possibility is that the cells they claim are adult neural stem cells are associated with a disease process in these individuals or some other cell type altogether.”

The human brain is full of cells that do divide and replicate throughout life called glial cells. These are the supportive and connective cells that enable neurons to do the job of conveying nerve signals. Glial cells are neurons’ pit crew. It’s possible that, in their efforts to identify neurons in progress, the study authors may have inadvertently included some glial stem cells in their analysis, Sorrells suggests.