Adult neurogenesis, human after all (again): Classic, optimized, and future approaches.

In this perspective article, we reflect on the recent debate about the existence of human neurogenesis and discuss direct, and also indirect, support for the ongoing formation, and functional relevance, of new neurons in the adult and aged human hippocampus. To explain the discrepancies between several prominently published human studies, we discuss critical methodological aspects and highlight the importance of optimal tissue preservation and processing for histological examination. We further discuss novel approaches, like single-cell/nucleus sequencing and magnetic resonance spectroscopy, that will help advance the study of human neurogenesis to its fullest potential - understanding its contribution to human hippocampal functions and related disorders like depression and dementia.