In 1998, Elizabeth Gould of Princeton University first reported neurogenesis in an adult primate when she observed that a significant number of new granule neurons (which get their name from their small size) were being produced in the hippocampus of adult marmoset monkeys.

She followed this discovery the following fall with the same observation in mature macaque monkeys, Old World primates closely related to humans. While scientists, including Gould, had previously observed neurogenesis in other animals, including canaries, rats and tree shrews, Gould’s discovery brought the focus to primates and supported Gage’s parallel findings in adult humans.

In March 1999, Gould extended knowledge about neurogenesis when she published research findings that indicate the number of neurons lost and new neurons generated in adult rats might be related to the degree of cognitive challenges an animal encounters. In other words, “use it or lose it” may have grounding in science.