Whether neurogenesis occurs in the adult human hippocampus remains controversial. Using sophisticated tissue preservation methods and highly specific tissue-processing methods (involving optimized fixation time and neuropathological examination of tissue samples), thousands of immature neurons (identified by the marker doublecortin) at various stages of differentiation were found in the dentate gyrus of heathy people, including adults in their eighties. By contrast, the number of these immature neurons declined with advancing Alzheimer disease, a change that might be involved in the memory deficits associated with the disorder.