Human adult neurogenenesis, yes or no?

While I was at school it was almost a dogma that you’d not get a neuron more than those you were born with. Later, at university we learned that actually there was a region in the human brain, namely the hippocampus (key region for memory formation) where there was indeed adult neurogenesis, that is, formation of new neurons.

Now, a new research article ¹ in the journal Nature comes once again to put human adult neurogenesis under question. In this article, the researchers used several different (immunohistochemistry) markers of neurogenesis in brain tissue samples from 59 human subjects going from fetal developmental stages to old age. They had several patient samples from each age range to avoid error due to sample status and used the embryonic samples as positive control for neurogenesis, and used various markers to avoid mislabelling of new neurons.

What they found was that, as expected, most neurogenesis takes place during fatal development and that after birth neurogenesis is greatly reduced to the extent that the oldest sample where immature neutrons were found corresponded to a 13-year old. Therefore, these findings seem to contradict the idea that there is new neutron formation in the adult human brain.

Now, obviously the results of this work raise a lot of questions and it is natural to wonder how do these results relate to the previous body of work in humans and/or other mammals. As discussed in an editorial accompanying the article, and mentioned in the discussion by Sorrels et al., some of the markers classically used in animal neurogenesis studies (DCX and PSA-NCAM or BrdU) can lead to false positives in humans. Moreover, there might also be issues relating to species differences like a longer maturation period for neurons in primates/humans than in rodents, where the continuous addition of neutrons would be a way of increasing plasticity that in humans would be mimicked by the longer neuronal development.

Be it as it may, and though more research is needed to settle the matter, it is yet another proof that in science there is no truth written in stone. Let’s just wait and see what the future holds…