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Can adults grow new brain cells?
Fair overview. This is not a simple question that can be answered with a Yes or No. It is a quantitative question at three levels:

1. What brain regions and neuron types?

2. What is the precise gain or turn-over of numbers of neurons per year?

3. What rates of change per year per type per brain region?

For humans we have essentially no hard data with which to address these three questions for structure or neuron type. Sadly this is also true for mouse with still shaky exception of the dentate gyrus and rostral migratory stream of one strain of mouse—C57BL/6J.

I still regard Pasko Rakic’s work as definitive—that in adult rhesus monkey females injected 4 to 6 times over several years with high levels of tritiated thymidine there is no evidence of adult neurogenesis in any brain region. Sure: proving the negative is a bitch, but these studies place a very low limit on levels of adult neurogenesis in primates—even in hippocampus. Meaninglessly low levels. And I have scanned this collection with Rakic.

The end of this review is on-the-mark: There are still very good reasons to be enthused about the POTENTIAL of adult neurogenesis. Being able to induce useful levels of adult neurogenesis would be a game changer. But reality and potential are different beasts.

I think this is probably right, dentate gyrus aside. Just flipping through the most recent publications, found this one: https://onlinelibrary.wiley.com/doi/full/10.1002/ana.27181
I'm curious if the body breaks down dead neuron cells in the central nervous system. There needs to be space for neurogenesis. For instance, the spinal cord can only be so large, constrained by the spinal column. If there's not enough fluid between the nerves a stricture can occur.
Yes it does—a process called apoptosis that is a “clean” way for a cell to die.
A follow up question(s) that occurs to me are: “Do neurons die?”

What is the lifecycle of a neuron? Does it get replaced? Will a neuron, whose connections to the broader brain decayed or otherwise went away, continue to “live”?

I’ll go ask ChatGPT, but spare this rigorous community the unreliable answers to my passive interest.

So without sharing what ChatGPT said, I will say that assuming it is correct it makes a lot of sense on this topic alone why individuals engaged in lifelong learning live longer and are less prone to Alzheimers.
In what sense could adult neurogenesis be useful? Stroke recovery? What about for "normal" people? And as opposed to just brain changes from traditional neuroplasticity?
Inducing regrowth of some cells could be a cure for parkinsons, for example.
CTE is cumulative. It adds over time, like hearing loss.
At a biological level, psilocybin induced a dose-dependent effect on neurogenesis, with a low dose increasing, and a high dose decreasing neurogenesis (62). (Again, mice)

https://pmc.ncbi.nlm.nih.gov/articles/PMC8461007/

This report has been taken a little out of context. In mice, a lot of things can be shown to stimulate neurogenesis.

Environmental novelty is even know to be correlated with neurogenesis markers in mice, which is a confounding factor when trying to determine if novel mind-altering substances are producing neurogenesis through some novel mechanism, or the mere experience of shaking up their world with drugs is just another novel experience.

That said, this is a good example of a case where we have a lot of research suggesting that mouse neurogenesis studies don’t translate well to humans. See the other well-written comment above as well as the associated article for more on the topic.

Unfortunately “mushrooms cause neurogenesis” has been taken as a given by a lot of mushroom enthusiasts, podcasters, and new age fitness guru types.

I missed “neurogenesis”. Most effects appears to be subtle changes in architecture of neurons.
Hasn't it been researched that psychadelics, namely lsd, are supposed to increase neuroplasticity?
  • sva_
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I think that has more to do with rewiring of existing neurons, rather than neurogenesis
Neuroplasticity is about rewiring the nodes, not creating new nodes.
On the topic of adult neurogenesis, I did find interesting Brant Cortright's "Neurogenesis Diet and Lifestyle".

It was probably the only divulgational book about the topic available at the time. It did seem to contain valuable information.

Unfortunately, it’s not really a good source for scientific information. Content like that can provide decent lifestyle suggestions overall, but the scientific basis on which they make their arguments are dubious at best.

Some people need a scientific sounding explanation before they’ll make any diet or lifestyle changes, so the material can still have a use. It’s just not a good source of scientifically accurate information about neurogenesis.

> not really a good source for scientific information

Probably so, but - while remaining of course based on academical articles - the perspective was that of a therapist - spendable information, not full caution. As said, it seemed to be the only work for the general public at the time.

> a scientific sounding explanation before they’ll make any diet or lifestyle changes

In a good basic commonsensical framework it's different: from e.g. "it seems that exercise also promotes some regeneration in the nervous system" follows "we have hints to value exercise even more". We most frequently work on hints, as that's what we most often only have.

I need to match this with e.g. some recent HN submission about the toxicity of some vitamines in the B group, making the abuse of supplement quite dangerous. Similarly, a prominent actress once declared her stroke an effect of extreme fitness regimes. So, you know, good commonsense... An extremist mentality applied to lifestyle (e.g. "Only/never eat butter, articles suggest") makes of science another miracles shop.

A+ for teaching me a new word!
  • bloqs
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one of the reasons neurogenesis slows down in adults is because of the chance of things going wrong, cancer or protein misfolds etc.

hubernan did a good episode on this which i cant find, but the episode was about improving the rate of learning amd our brain. essentially he asserts that we seem to have a strong mechanism for brain growth in desperate circumstances, like hunting for food while very hungry. I will try to find and edit this comment

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I can see the cancer angle, yet many parts of the body seem to have no trouble regenerating again and again without being particularly more prone to cancer.
Very likely answer is no: https://slatestarcodex.com/2018/04/04/adult-neurogenesis-a-p...

... but genome and local cell environment is malleable, and it is quite likely that some combination of molecular signals could be found to induce it.

This overview is perfect. Lots of misplaced enthusiasm for dubious data. Counting neurons is a hard business and very few practitioners do it correctly.
Coincidentally this was the topic of the latest episode of "The Studies Show" podcast [0]. It covers similar aspects including carbon 14.

[0] https://www.thestudiesshowpod.com/p/episode-74-neurogenesis - There is a transcript available from this page.

So does lion's mane work or no? What about regular sauna sessions?

I seem to remember that they alledgedly induced neoneurogenesis.

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It may also be an irrelevant question in light of connections research that shows circuits are more important than regions of cells.
Isn't it well established that pregnant women host new brain cells that migrate from the fetus?
Not that I have ever heard. How could that be established?
https://pmc.ncbi.nlm.nih.gov/articles/PMC2633676/ (2007)

https://academic.oup.com/clinchem/article/67/2/351/6071463?l... (2020)

https://en.wikipedia.org/wiki/Microchimerism#Fetomaternal_mi...

IIR, substantial and sustained fetal cell presence in the mother is often a sign that things are going wrong.

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