Brain tissue samples suggest we stop growing new neurons in our early teens

[ramblerman]

I see this as a positive. I always lamented the idea that as we grew older we generated less and less neurons, and thus our learning capacity decreased (I thought).

But it seems even young university students are no longer generating neurons. Nor are the 30 year olds learning new languages or switching careers.

It seems neuron growth thus has nothing to do with 'plasticity' or our capability to learn.

* disclaimer: I know very little of neurology so please correct any false assumptions.

[heldrida]

True! But someone who learns to play the guitar, or a language at 8 ~ 15 years old shows skills that are very difficult to master (if not impossible) when you are older. There's a lot of evidence of this if you talk with guitar teachers, someone who moved and start speaking a different language when adult, etc...

[redka]

Considering that as we age we lose some of our neurons - even if not _because_ of aging itself but for other reasons such as drugs or disease - there still could be an observable difference in both 'plasticity' of our brain and our capability to learn.

[shaki-dora]

The neurogenesis hypothesis was always more about mood/mental health rather than learning, I believe.

[NutriSugar]

I think learning is more about losing neurons, not creating it. Or meatspace neural netowrks are less about changing weights and more about pruning connections.

[sevenfive]

I mean, we already know the differences between 20- and 30- year olds from simple observation. So it's not really positive or negative.

[jmcgough]

This article has some good insights from other researchers and their different opinions on the study:

https://www.theatlantic.com/science/archive/2018/03/do-adult...

Adult neurogenesis in rats was my thesis focus, so it's interesting that all the rat work we did may or may not translate over to humans.

[jey]

I'm gonna wait for the replication, as always.

But what about all that exercise-induced BDNF-mediated neurogenesis stuff? Was that only observed in mouse models?

[SubiculumCode]

Neurogenesis in the hippocampus and olfactory bulbs is ongoing trough the lifespan. I am presuming this is not about that neurogenesis.

[kristiandupont]

Absolute pitch is something that supposedly can only be learned before the age of 6 but the drug Valproate seems to reopen this window.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3848041/

[rorykoehler]

I learned it as a teenager and lost it in my 20s. Like anything I learned it through practice and familiarity. Once I stopped working in music production I slowly lost my absolute pitch too. Similar to the way I used to be able to speak French but now can only string a few words together.

[CuriouslyC]

I suspect that valproate works by increasing BDNF levels. Exercise also increases BDNF levels, and a diet high in fermentable fiber has been linked to increases in BDNF as well, through increased short chain fatty acid production. It is worth mentioning that valproic acid is just a branched-chain short chain fatty acid, so it is likely that many of its effects are similar to those from short chain fatty acids derived via dietary fiber fermentation.

[bsder]

I thought they used isotope analysis from nuclear testing fallout to prove that the neurons in the brain are between 15-20 years old on average? How do they reconcile this?

http://www.physicscentral.com/explore/action/nuclear-neurons...

[jey]

A likely possibility: the molecules get replaced, but it's still the same cell.

[divbit]

Afaik nature has good stuff, but it's not like a 'research journal' it's more popular stuff. A quote from the article: "There are only a handful of studies out there that have already attempted to look at this, and they came to wildly different conclusions." So, although I didn't look into this more deeply, it seems to me there is wide room to not take this popular article as 'full confirmation'.

[otakucode]

This worries me. First, any study of neurology it must be kept in mind is done on a specific population. The neurology of a Papua New Guinea highlander and an upper middle class white kid from the suburbs of NYC are not going to have the same brain development. Brain development does NOT proceed as a consequence of aging. This is a dangerous and destructive myth that gets perpetuated all the time. Brain development proceeds as a consequence of experience. If you eliminate experience from a persons life, you will eliminate brain development.

We can see this clearly in the very young. An infant must master binocular vision by about 3 weeks old, or else they will never master it. Putting an eyepatch on an infant because they are "not ready" for binocular vision or because their brain "isn't mature" in the region responsible for that would damage them for life. A child must be exposed to the general concepts of language before about age 5 or else they will remain incapable of learning any sort of language-based communication for their entire life. Likewise if you were to restrict them and keep them away from language exposure because their brains are 'not mature' or because they're 'not ready' for it or whatever, you would do them grievous harm by actively preventing brain development.

There are similar critical periods and developmental milestones like the Existential Crisis where children develop an understanding of death as the end to life and understand their own mortality around age 10. It was always thought that neuroplasticity pretty much disappeared after adolescence. I've always wondered if that was a consequence of the way the life experience of a person in a western society changes after adolescence. That is typically when almost all experience of novelty comes to a grinding halt. Jobs are taken up, spouses found, routines established. And without unique experience providing intense stimulus to a brain, it will stop developing. Absent those stimuli, it never would have developed in the first place. It is the origin of growth.

If we start to see neuroplasticity decreasing even earlier in members of our society, I would not be terribly surprised given the degree to which adolescence has been either criminalized or heavily regulated. And we will pay the price for that.

[azinman2]

Unless it happens somewhere other than the hippocampus..

[chrisabrams]

I was wondering as well, is it possible that there’s another part that it happens instead?

[MarlonPro]

Is this a blow to neuroplasticity?

[jateenjoshi]

Not this result in itself. Neuroplasticity refers to the ability of existing neurons of creating/pruning connections to other neurons.

However, separately, there is scientific evidence to show that neuroplasticity decreases after adolescence.

[robbrown451]

I appreciate the suggestion, but how am I supposed to do that?

[taneq]

And why would I listen to a brain tissue sample anyway?