One of the references cited in Linking adult neurogenesis to Alzheimer’s disease was https://www.nature.com/articles/s41591-019-0375-9 “Adult hippocampal neurogenesis is abundant in neurologically healthy subjects and drops sharply in patients with Alzheimer’s disease” (not freely available).

This 2019 Spanish human study used improved techniques to find:

“Adult hippocampal neurogenesis (AHN), confers an unparalleled degree of plasticity to the entire hippocampal circuitry. Direct evidence of AHN in humans has remained elusive. Determining whether new neurons are continuously incorporated into the human dentate gyrus (DG) during physiological and pathological aging is a crucial question with outstanding therapeutic potential.

By combining human brain samples obtained under tightly controlled conditions and state-of-the-art tissue processing methods, we identified thousands of immature neurons in the DG of neurologically healthy human subjects up to the ninth decade of life. These neurons exhibited variable degrees of maturation along differentiation stages of AHN. In sharp contrast, the number and maturation of these neurons progressively declined as AD advanced.

These results demonstrate the persistence of AHN during both physiological and pathological aging in humans and provide evidence for impaired neurogenesis as a potentially relevant mechanism underlying memory deficits in AD that might be amenable to novel therapeutic strategies.”

The control group was 13 neurologically healthy deceased people aged 43 to 87. The AD group was 45 deceased people, distributed among the six Braak stages of the pathology, aged 52 to 97.