It's a new study that disagrees with previous findings, which is what science is all about. As a Nature paper, the strict length requirement on the paper unfortunately don't allow the authors to discuss the differences with previous findings in much detail. However, there is a [supplemental discussion](https://media.nature.com/original/nature-assets/nature/journal/vaop/ncurrent/extref/nature25975-s1.pdf
) (starts on page 5), something I have never seen before, that goes over several previous studies that found adult neurogenesis and explains why those results could be wrong. Clearly, the authors are aware that their results will be controversial in light of previous work on the subject. Most of their discussion seems to center on the methods used in the previous studies and why they could be unreliable or poorly suited for the job.
Maybe this study will shift the scientific consensus on adult neurogenesis and maybe it won't. Most likely, it will result in more research aimed at clarifying the issue. Eventually, consensus will shift, or it won't, depending on the data. This is how science works.
EDIT: /u/zmil posted [this blog post](http://snyderlab.com/2018/03/07/wtf-no-neurogenesis-in-humans/
) from another researcher in the field downthread, and I wanted to give it visibility here. It gives readable and reasonably brief summary of the adult neurogenesis controversy and the significance of this new paper.
The other day, I ran across this [really good blog post](http://snyderlab.com/2018/03/07/wtf-no-neurogenesis-in-humans/
) on this paper from another researcher in the field of neurogenesis. It's very even-handed and readable for non-specialists.
His summary of key points:
>-the quality of the histology is excellent, which is critical for interpreting any study, especially studies of human tissue
>-the use of young samples is a plus, since this demonstrates that they are capable of identifying neurogenesis using the same techniques that are used in the older brains
>-their definition of immature cells are those that express both of two markers that are commonly used in animal studies: DCX and PSA-NCAM. This is more stringent criteria than is common but it is warranted because they show that either marker on their own can be non-specific (and identify mature neurons or glia)
the downside is that there could be legitimate immature cells that only express one of the markers, that would be missed in the analyses
>-given species differences (between well-understood animals and poorly-understood humans) and methodological differences between studies, more research is needed to reconcile these negative findings with previous positive evidence for adult hippocampal neurogenesis in humans
>-it suggests a number of directions for future research: better comparisons between rodents and longer lived mammals, the possibility that neurogenesis is more relevant at earlier developmental stages, developing neurogenic strategies for repaired the damaged brain…
In general, we would not expect a single scientific article to alter the content of an encyclopedia type article, although in the case of wikipedia, this might cause a restructuring of the encyclopedia article to include a list and/or discussion of studies showing evidence for adult neurogenesis and those showing the opposite. It isn't necessarily the goal of an encyclopedia to make a decision on whether a particular topic is correct or not, but rather to record the history of the idea and reflect on current thinking.
The Nature study asserts that neurogenesus is rare or absent in adult hippocampus, which is a specific brain region with a specific developmental trajectory. This does not eliminate or even directly address the possibility that adult neurogenesis may occur in other brain regions, or even in the hippocampus under conditions they didn’t look at.
Technological advances, particularly in optogenetics and scanning/visualization techniques, have had a big effect on what it is physically possible to investigate and at what level of detail, so this allows discovery of new evidence that sometimes contradicts evidence collected using older, less precise techniques & technologies.
My previous professor, who is prominent in the field, indicated to me that a rebuttal article is being crafted right now to put these results in context. In their words, there are three lines of evidence that strongly support adult neurogenesis and its functional importance, and this work demonstrates a failure to reproduce one of the three lines, which they emphasize is the weakest line. So stay tuned! I wish I could give you more details, but it’s still ongoing. Please do continue to follow this topic.
Maguire, Frith and others have several great papers demonstrating increased hippocampal density in London taxi drivers (over time, and also versus bus drivers who follow fixed routes). So how is increased hippocampal density arising in adults in the absence of neurogenesis? Increased dendritic branching? Neurogenesis in a different hippocampal area than the very specific region considered by this paper?
I don’t mean to hijack your thread (and I won’t, because on one will ever see this comment, in all likelihood), but this is why it’s so important to talk in terms like “the data seems to currently show” and “we think that...” rather than harder terms like “science says...etc”. Science doesn’t SAY anything. Our studies say things, and they may or may not be well-designed and meaningful.
I'm an ex-researcher, now on the industrial, translation side. So basically, my opinion will be (and maybe should be) seen with bias.
That said, yeah, this article is contradictory to what you've perhaps read before. Great. These articles aren't meant to be digested by the general public to be translated by people not directly involved in relevant research topics. If they were, these articles would be required to have a much more non-scientific vocabulary.
These Nature (and Science, Cell, PNAS, etc) articles are meant for researchers who are scoping these discussions. They aren't looking for punchlines..or breakthroughs..or hype. They are looking to market their research to people who see this as insight/direction/non-direction. Nothing else.
So, I'm not trying to be THAT guy here...BUT, if you're not in the field, PAY NO ATTENTION TO THESE ARTICLES, imho. Don't read too much into it, and take it as breaking research that is up-and-coming -- even exciting. But that's it.
Just my two cents here.
From someone who isn't in the field, I think this study does a good job at showing that neurogenesis through pathways associated with development drops off at a young age and becomes undetectable in adults. That being said, maybe neurogenesis - and here I mean the production of new neurons from any source - in adults occurs through a different pathway, for example, via glial intermediates. Therefore I would say that it's premature to make the assertion that neurogenesis does not occur in adults at all.
I think the new study talks about the primate hippocampu specifically.
> that since the 1970's its been well established that adult neurogenesis is an ongoing phenomenon.
Well, the evidence isn't quite that unambiguous. Adult neurogenesis has been a subject of significant research interest and investigation largely *because* - even in papers that support it's existence - it is still seen and presented as an infrequent phenomenon that requires a specific set of conditions, may respond differently to different kinds of cellular damage (vs. a part of healthy brain maintenance), and may be restricted to certain neural subtypes and/or brain regions. Brain/CNS damage is still considered to be (mostly) a permanent change that may be compensated through plasticity, but not healed through cellular renewal and regeneration. It's definitely not like epithelium that undergoes constant self-renewal and easily observed lifelong new cell generation.
I found one major study examining the extent of renewal:
>In adult humans, 700 new neurons are added per day *[in the hippocampus]*, corresponding to an annual turnover of 1.75% of the neurons within the renewing fraction... *[which this study estimates is ~a third of the hippocampal volume]* [[Spalding et al, 2013, Cell](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4394608/
So, 700 neurons is not zero, but also not that many. For reference, the hippocampus contains 40.2x10^6 neurons. This is very much a needle-in-a-haystack problem, even to those who are bringing evidence in support.
the first quote clearly says neurogenesis is continuous in specific regions of the brain. The second says it does not happen in two specific regions. There are many specific regions of the brain. Clearly the researchers did not research the correct specific regions.
The thing about amazingly high-tier journals like Nature and Science is they only publish results that are controversial or attempt to change the majority opinion. This has a consequence of almost every article in nature being wrong as things that change the majority opinion tend to not be true when the majority opinion is based on good evidence and data. When you see an article in one of these journals you should pretty much just log it in the back of your mind and then check on it in 5 years to see if it's held up. Sometimes the consensus has changed in favor of the new article but usually it hasn't and the one controversial article was just disproven.
So how do I make new memories? I mean, that happens right? I'm 44, I'm still learning. Just started a new job and I'm learning new skills.
Neurons rewire themselves right? So, IF I'm not making new neurons, is that how I learn new skills?