Adult Human Brains Do Not Produce New Neurons, Study Suggests (newatlas.com)

Rich Haridy reports via New Atlas: New research from scientists at UC San Francisco is challenging half a century of conventional wisdom by suggesting the human brain may cease producing new neurons beyond childhood. While the divisive study may prove a blow to some research aimed at birthing new neurons to battle neurodegenerative disorders, it offers a new perspective on how the human brain can adapt in later life without such a capability. The team generated its data by studying brain specimens of 59 subjects, from babies to the elderly. The strategy was to look for the presence of young neurons or dividing cells by using certain antibodies that bind to those cells of interest. The focus was on the hippocampus region of the brain, known to be crucial for memory, and a comprehensively studied area previously suggested to be a key location for neurogenesis. The results were fairly comprehensive. Young or immature neurons were identified in plentiful volumes in prenatal and newborn samples but the rate consistently declined over childhood. The oldest sample that immature neurons were found in was 13 years of age, and adult samples displayed no evidence of new neurons. The study has been published in the journal Nature.

Comments

Wrong.

[Qbertino]

The study found that certain indicators associated with the growth of cells in young mamals/people couldn't be found in grown-ups. This doesn't contradict the growth of cells in adult brains. The study isn't disputed as heavyly as the conclusions drawn are, but they are disputed.

Re:Wrong.

[macklin01]

There's a big difference between growth of cells (they get bigger) and proliferation of cells (they divide to create new cells), and so it's important to be careful. (I've been working on modeling both cell growth and cell division for a good while, mostly in cancer and a little in tissue engineering and synthetic biology. e.g., here.)

I looked at the study. They stained for Ki-67, the gold standard immunohistochemical marker for cell division. Cells that are actively cycling--in late G1, S, G2, and M phase, and a smidgen of G1 phase after division because Ki67 protein doesn't instantaneously degrade--stain positive for this marker. In particular, it is a nuclear marker, so the stain is localized to the cell nucleus, and the stain is very definitive. It's one of the easiest immunostains to do image processing on, because you can do nuclear segmentation, then analyze the colors in the segmented nuclei to see if they stained positive or negative for Ki-67.

And that Ki-67 marker was virtually non-existent in the region of interest in all the samples above 13 years old. See Figure 2. This is *the* universal gold standard marker for cell division used across pathology and experimental biology. So yes, the study indeed found no proliferating cells in the GCL. And then they used this "young neuronal cell" marker (DCX+PSA-NCAM+ cells) to further confirm what they already saw in Ki67.

Also, the Nature link is the *summary* of the paper, and not the actual paper. It's pretty common for the big journals to ask for a non-involved scientist in the same field to write a summary and commentary when a potentially controversial or significant paper comes out. Here's the actual paper.

Re:Wrong.

[macklin01]

No problem, and thanks for reading and replying.

I was confused on that, too, and neurobiology is pretty far from my regular work. Part of the problem is that there's a lot going on here: plasticity and differentiation (cell adaptations, transformations from one phenotype to another, differentiation, etc.), cell proliferation, tuning of connections, etc. It's a messy area with lots of new and sometimes contradictory data coming out.

From what I understand, there's a lot of plasticity in the brain as an adult: far more than was originally appreciated. I thought that we "knew" there were no new brain cells, and then we "knew" there were, and now we may "know" there aren't. That's the nature of evolving science, as others point out. And imprecise science communication--and imprecise English--doesn't help, either. Even biologists can get tripped up: we talk about tumor growth and cancer cell population growth, but we really primarily are talking about cell division there.

And there are all sorts of neat surprises. It was found that glial cells (a type of brain cell responsible for maintaining brain structure) can transdifferentiate into endothelial cells (which make blood vessels). See this PNAS paper and this one. This has all sorts of implications for gliomas and other brain cancers. And God only knows what other surprises are waiting to be found.

I suppose that's another reason they looked at the "new neuronal cell" marker: to see whether other cells could become new neuronal cells by transdifferentiation or other plastic processes. Biology is weird. :-)

Unless you take Ayahuasca

[Anonymous Coward]

For a long time, scientists believed that no new neurons are born in the brains of adults, meaning that when our existing brain cells become damaged or die, they are not replaced. However, it was later discovered that neurogenesis – meaning the creation of new neurons – does in fact in occur in the hippocampus, a brain region associated with memory. Unfortunately, the rate of neurogenesis is not always sufficient to replace all of our damaged neurons as we age, which is why many people suffer from dementia and other age-related cognitive deficiencies. Fortunately, a study conducted by the Beckley/Sant Pau Research Programme, and published in the journal Scientific Reports, reveals that certain compounds present in the psychedelic Amazonian brew ayahuasca actually stimulate the birth of new neurons.

Researchers placed harmine and tetrahydroharmine – the most prevalent alkaloids in ayahuasca – in a petri dish with hippocampal stem cells, and found that this greatly increased the rate at which these cells developed into fully mature neurons. The results of this study were first presented at the Interdisciplinary Conference on Psychedelics Research in 2016, and represent the first evidence that components of ayahuasca have neurogenic properties, thereby opening up a wealth of possibilities for future research.

We are currently conducting additional experiments to discern the magnitude of the observed effects, as well as undertaking studies on live animals. The replication of the present findings in vivo would represent a major breakthrough in mental healthcare, with potential applications ranging from treating neurodegenerative and psychiatric disorders to redressing brain damage associated with stroke or trauma.

---
http://beckleyfoundation.org/ayahuasca-stimulates-the-birth-of-new-brain-cells/

Re:50 Years?

[hey!]

That's the way science works. You keep gathering more evidence and as it mounts you sometimes have to change your mind. The eventual goal is to tackle complex questions.

What makes a question complex? Evidence can be found for more than one possible answer. The world abounds in questions like that.

If evidence in principle can force you to change your mind, then why keep collecting it once you've made up your mind? There's two good reasons. One is that once you've collected a lot of evidence, you don't have to change your mind every time a bit of contradictory evidence comes up, as long as the balance of evidence weighs in a certain direction. For example this study looked for new neurons and didn't find any. The news media's poor understanding of science means they jump to the conclusion that there aren't any new neurons. But at this point in the evidence gathering it's more likely they didn't do a good job of looking for them.

The second reason is to learn to ask better questions. Thirty years ago we believed the brain was essentially static except for decay once you reached maturity. However at this point there is almost incontrovertible evidence that brain is far, far more plastic than we believed possible -- e.g. documented cases of epilepsy patients treated with a hemispherectomy regaining motor control of the affected body side. We assumed that this was because those patients grew new neurons, but if this finding holds up, we then have to ask: what is the mechanism of brain plasticity?

Or it may be that this finding describes the usual case but in unusual ones the brain can rewire itself with new neurons. We don't know yet, but the point was until we looked we didn't understand well enough to know what we don't know.

Re:Thats' science!

[religionofpeas]

Actually, the studies were not done with eggs, but with high amounts of isolated cholesterol. And the cholesterol wasn't given to humans but to rabbits. Rabbits, who don't usually eat eggs or meat as part of their diet, are very bad at handling high amounts of cholesterol.

Alright

[DontBeAMoran]

Childhood = build the internet
Adulthood = route around damage, like the internet