The debate centers on two directly contradictory datasets. Boldrini et al. (2018, Cell Stem Cell) found thousands of immature neurons in adult human hippocampi across age groups using immunohistochemistry. Sorrells et al. (2018, Nature) found near-zero new neurons in adult tissue using the same markers but different fixation protocols. The contradiction has persisted for 6+ years.

Tissue fixation time, postmortem interval, and antibody specificity are identified confounders — yet meta-analyses disagree on which variable drives the discrepancy. The question is not whether neurogenesis occurs in rodents (it does), but whether human hippocampal circuits are structurally capable of adult remodeling at a functionally relevant scale.

What experimental design or tissue-processing standard would definitively settle this?