Yikes. It isn’t generally a good idea to put all your faith in a single new study, but it’s an interesting thought:
So it’s not like any one person made a spectacular mistake anywhere along the lines. Most of the studies done were in rats, and 100% correct. A few studies were done in humans, and may have gotten the wrong answer in a very difficult domain, while also hedging their bets and admitting they were trying something hard. It was only on a structural, field-wide level that all of this came together into people just assuming that adult human neurogenesis had to happen and be important.
…or at least, that’s the optimistic take on it. But I can’t help thinking – antidepressants work in humans, which suggests that the people who found neurogenesis was necessary for antidepressant effects must have just been plain wrong. And if exercise has antidepressant effects in humans, then the claim that those effects are neurogenesis-mediated must be wrong too. And, uh, humans form spatial and temporal memories, so unless we do this by a totally different mechanism than the ones rats use, people must have been wrong when they said neurogenesis was involved in that. ECT? Works in humans. Brain plasticity? Happens in humans. So maybe it would be better to say that the original claim that adult neurogenesis happens in humans seems innocent and understandable – but if the new study is true, that suggests that a lot of the followup claims must have been imaginary. Anything that focuses on a process that happens in humans and says “neurogenesis causes this” must not only be wrong to extend the results to humans, but must be under strong suspicion of being wrong even about rats, unless rat brains and human brains accomplish the same basic tasks through totally different mechanisms (eg antidepressants work on rats but for different reasons than in humans).
Coverage of the study is here… I’m still reading it over.