Could adult hippocampal neurogenesis be relevant for human behavior?

Although the function of adult neurogenesis is still unclear, tools for directly studying the behavioral role of new hippocampal neurons now exist in rodents. Since similar studies are impossible to do in humans, it is important to assess whether the role of new neurons in rodents is likely to be similar to that in humans. One feature of adult neurogenesis that varies tremendously across species is the number of neurons that are generated, so a key question is whether there are enough neurons generated in humans to impact function. In this review we examine neuroanatomy and circuit function in the hippocampus to ask how many granule neurons are needed to impact hippocampal function and then discuss what is known about numbers of new neurons produced in adult rats and humans. We conclude that relatively small numbers of neurons could affect hippocampal circuits and that the magnitude of adult neurogenesis in adult rats and humans is probably larger than generally believed.

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► The functional importance of adult-born neurons depends on their properties and numbers.
► We calculate higher numbers of immature and/or adult-born neurons than expected.
► Relatively few new neurons could signficantly impact circuit function.
► In the human brain, there may be sufficient adult neurogenesis to affect behavior.