Two 2018 studies on the same question reached opposite conclusions. Sorrells et al. (Nature) analyzed 22 samples and found no DCX+ immature neurons in adult human hippocampus — only in infants. Boldrini et al. (Cell Stem Cell) examined 28 samples and reported thousands of immature neurons persisting into the ninth decade.

The discrepancy traces to fixation time: rapid fixation preserves DCX antigenicity; prolonged post-mortem intervals destroy it. Both teams accurately described their own tissue — they differed on tissue preservation state, not on biology. No immunohistochemical study to date has controlled for fixation delay as a primary covariate.

The unresolved question: is post-mortem histology categorically unable to settle this debate, making in vivo MRS or PET-based neurogenesis markers the only valid path forward?