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What Mislead Scientists on Neurogensis?

MasturDbtor
Posts: 45
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3/30/2015 4:11:47 AM
Posted: 1 year ago
Science used to think that in adulthood it was impossible for the brain to generate new cells.

And now we know that at the very least neurogenesis occurs in the hippocampus. We also know that it relates to our experiences. For instance London Taxi Drivers grew new neurons on the job.

It makes me wonder what evidence did they have before that they were going on to say positively that neurogenesis could not occur, as opposed to saying that it was inconclusive and that they did not know whether it could occur or not?

Anybody know this? I'm curious to know what mislead scientists on this.
UndeniableReality
Posts: 1,897
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3/30/2015 1:04:17 PM
Posted: 1 year ago
At 3/30/2015 4:11:47 AM, MasturDbtor wrote:
Science used to think that in adulthood it was impossible for the brain to generate new cells.

And now we know that at the very least neurogenesis occurs in the hippocampus. We also know that it relates to our experiences. For instance London Taxi Drivers grew new neurons on the job.

It makes me wonder what evidence did they have before that they were going on to say positively that neurogenesis could not occur, as opposed to saying that it was inconclusive and that they did not know whether it could occur or not?

Anybody know this? I'm curious to know what mislead scientists on this.

I think this was more of a belief based on not being able to find evidence of neurogenesis in adult birds and mammals despite looking for it. Better technology and methodologies eventually provided the evidence. To some extent, I would agree that the conclusions made about neurogenesis were premature, but I don't know enough about the history to be confident in that statement.

These are two of the first papers showing neurogenesis in adult mammals, and they discuss a little bit the basis for believing neurogenesis didn't occur in adults.

Hopefully the partial citations are sufficient to find them.
[1] Altman and Das. (1965). Autoradiogrpahic and HIstological Evidence of Postnatal HIppocampal Neurogenesis in Rats.
[2] Atman and Das. (1965). Postnatal Neurogenesis in the Guinea-pig.
RuvDraba
Posts: 6,033
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3/30/2015 3:13:03 PM
Posted: 1 year ago
At 3/30/2015 4:11:47 AM, MasturDbtor wrote:
at the very least neurogenesis occurs in the hippocampus. We also know that it relates to our experiences. For instance London Taxi Drivers grew new neurons on the job.

It's not so clear-cut, MD. Neuroscientists seem to be still homing in on the key questions, gathering data, and arguing over how to interpret it. Here's a brief historical summary, as best I understand it.

Over-all, neuroscientists want to find ways for neurons to regenerate, as it would allow treatment of brain injuries such as strokes, for example, and damage from disease. However scientists must be skeptical and meticulous,and their experiments must be ethical -- especially with humans.
"Everyone wants to believe that functional neurogenesis happens in adult humans, everyone wants to believe that we can repair damaged brains. But there's precious little evidence for it."
-- Andrew Lumsden, head of MRC Centre for Developmental Neurobiology, King's College.

For most of the 20th century, neuroscientists thought the brain stopped generating neurons after gestation. This view was first advanced by Nobel-winning 19th century anatomist Santiago Ramon y Cajal, whose foundational study of the neuron gave neuroscience an anatomical basis for further development.
"Once development was ended the founts of growth dried up irrevocably. In the adult, the nerve paths are immutable."
Santiago Ramon y Cajal

At the time, the evidence against was pretty strong: rapid neurological production had been observed in the foetuses of humans and other animals; the production seemed to end at birth when the infant started learning with the neurons already produced, and it was known that (for example) stroke victims suffering brain injury did not suffered long-term functional disability, e.g. with speech and movement, and had to relearn to use the damaged brains they had.

Theoretically, there was also the concern that new neurons couldn't take the place of old, because the old ones had very specific function and connections. New neurons could actually interfere with effective brain function, and there was thought to be an evolutionary pressure for them not to occur in adults, so there was not a lot of scientific effort in looking for adult neurological regeneration.

However, in the 1980s came the first accepted evidence that some adult animals could regrow their brains. It turns out that male canaries learn new songs every year to attract mates. With only small brains, the canary's song-producing brain-regions shrink at the end of breeding season, only to regrow next Spring.
"Our results showed beyond reasonable doubt that neurons are born in adulthood and incorporated into existing circuits."
Fernando Nottebohm, Rockerfeller University, New York

In 1992, it was shown that this can also occur in mammals. Samuel Weiss and Brent Reynolds at the University of Calgary isolated cells from the brains of mice that seemed to function as stem cells: in the laboratory, they divide repeatedly and can produce neurons and other kinds of brain cells, and seems to play a role in learning and memory, including learning new smells. This was also independently confirmed in macaques -- a kind of primate -- and therefore suggested that humans might see the same: our first whiff of hope.

In 1998, neurogenesis in adult human hippocampuses was reported in Nature.
Human brain tissue was obtained postmortem from patients who had been treated with the thymidine analog [...] BrdU [...]. Using immunofluorescent labeling for BrdU and for one of the neuronal markers, NeuN, [...] we demonstrate that new neurons, as defined by these markers, are generated [...] Our results further indicate that the human hippocampus retains its ability to generate neurons throughout life.
Fred H Gage et al, Neurogenesis in the adult human hippocampus, Nature Medicine 1998 [http://www.nature.com...]

This discovery produced worldwide press coverage, in part because it chimed with the growing belief in neuroplasticity. However the study has not been repeated because it requires a significant number of cancer patients who have already been treated with BrdU. Yet there is supporting evidence from another brain-staining technique, and more evidence for stem cells in the human brain thanks to people who have surgery for epilepsy -- excised hippocampuses also may contain stem cells.

But as promising as these results may be, the case for human neurogenesis still isn't proven. For example, Pasko Rakic, head of Yale's neurobiology department, having written articles both for and against human neurogenesis, was critical of Gage's work, arguing that BrdU can itself induce cell division, can mislabel dying cells, and argued over how to identify new neurons reliably. Other evidence against includes carbon-14 decay data from victims near atomic bombs. [http://www.pnas.org...]

So, science is still gathering evidence and working through it. There's not just scientific reputation involved here -- there's human welfare at stake, so this question will get exhaustively researched on any skerrick of hope. However, the brain is complex, human neurological experiments are restricted by ethical concerns, so useful experiments are few, and progress is painstakingly slow.

This kind of contention is business-as-usual for science, however when popular media get involved they often take a side -- reporting a single experimental result as a final conclusion, for example, or drawing connections between possibly unrelated scientific results (for example, do the hippocampuses of London taxi-rivers grow due to there being more neurons, or the tissue itself growing?)

This can give the inadvertant appearance of scientists holding back progress, more than testing it skeptically. I think that's what's happening here.

I hope that helps.

(Quotes and links sourced from Mohab Constandi, The mystery of the missing brain cells, New Scientist 21 Feb 2012 [http://www.newscientist.com...])
UndeniableReality
Posts: 1,897
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3/30/2015 4:03:51 PM
Posted: 1 year ago
At 3/30/2015 4:11:47 AM, MasturDbtor wrote:
Science used to think that in adulthood it was impossible for the brain to generate new cells.

And now we know that at the very least neurogenesis occurs in the hippocampus. We also know that it relates to our experiences. For instance London Taxi Drivers grew new neurons on the job.

It makes me wonder what evidence did they have before that they were going on to say positively that neurogenesis could not occur, as opposed to saying that it was inconclusive and that they did not know whether it could occur or not?

Anybody know this? I'm curious to know what mislead scientists on this.

You may also want to look up some of the work by Neil Burgess and Sue Becker who are current players on this topic. The Byrne Becker Burgess model might be fun to play with as well, if you're familiar with Matlab coding. I can send you a link to the code if you'd like.
RyryMase
Posts: 43
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3/31/2015 3:18:20 AM
Posted: 1 year ago
At 3/30/2015 4:11:47 AM, MasturDbtor wrote:
Science used to think that in adulthood it was impossible for the brain to generate new cells.

And now we know that at the very least neurogenesis occurs in the hippocampus. We also know that it relates to our experiences. For instance London Taxi Drivers grew new neurons on the job.

It makes me wonder what evidence did they have before that they were going on to say positively that neurogenesis could not occur, as opposed to saying that it was inconclusive and that they did not know whether it could occur or not?

Anybody know this? I'm curious to know what mislead scientists on this.

I learned about the taxi drivers and neurogenesis in one of my psychology classes like a year ago. The reason this is relatively new is because of the ideological switch from behaviorism to cognitivism in recent time, and new technology.

New technology has given us the ability to get an image of our brain without us having to be dead. CT scans for example.

The most important reason is that behaviorism ruled psychology until 1950. Nothing was studied outside of that until cognitivism started gaining momentum eventually ruling out behaviorism as the study of psychology. Behaviorism is conditioning. While cognitivism is thinking. So if you started studying thinking then you start to look at the brain and it's neurons. If you study behaviorism then you get Pavlovs stupid dog experiment.
UndeniableReality
Posts: 1,897
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3/31/2015 9:50:12 AM
Posted: 1 year ago
At 3/31/2015 3:18:20 AM, RyryMase wrote:
At 3/30/2015 4:11:47 AM, MasturDbtor wrote:
Science used to think that in adulthood it was impossible for the brain to generate new cells.

And now we know that at the very least neurogenesis occurs in the hippocampus. We also know that it relates to our experiences. For instance London Taxi Drivers grew new neurons on the job.

It makes me wonder what evidence did they have before that they were going on to say positively that neurogenesis could not occur, as opposed to saying that it was inconclusive and that they did not know whether it could occur or not?

Anybody know this? I'm curious to know what mislead scientists on this.

I learned about the taxi drivers and neurogenesis in one of my psychology classes like a year ago. The reason this is relatively new is because of the ideological switch from behaviorism to cognitivism in recent time, and new technology.

New technology has given us the ability to get an image of our brain without us having to be dead. CT scans for example.

The most important reason is that behaviorism ruled psychology until 1950. Nothing was studied outside of that until cognitivism started gaining momentum eventually ruling out behaviorism as the study of psychology. Behaviorism is conditioning. While cognitivism is thinking. So if you started studying thinking then you start to look at the brain and it's neurons. If you study behaviorism then you get Pavlovs stupid dog experiment.

I'm not sure how this relates to the OP actually. While much of what you're saying is correct, behaviourism and cognitivism never applied to neurobiology, and postnatal neurogenesis was discovered via histology.
MasturDbtor
Posts: 45
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4/1/2015 12:39:53 AM
Posted: 1 year ago
At 3/30/2015 4:03:51 PM, UndeniableReality wrote:
At 3/30/2015 4:11:47 AM, MasturDbtor wrote:
Science used to think that in adulthood it was impossible for the brain to generate new cells.

And now we know that at the very least neurogenesis occurs in the hippocampus. We also know that it relates to our experiences. For instance London Taxi Drivers grew new neurons on the job.

It makes me wonder what evidence did they have before that they were going on to say positively that neurogenesis could not occur, as opposed to saying that it was inconclusive and that they did not know whether it could occur or not?

Anybody know this? I'm curious to know what mislead scientists on this.

You may also want to look up some of the work by Neil Burgess and Sue Becker who are current players on this topic. The Byrne Becker Burgess model might be fun to play with as well, if you're familiar with Matlab coding. I can send you a link to the code if you'd like.

I would. Thank you.
UndeniableReality
Posts: 1,897
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4/1/2015 9:52:52 AM
Posted: 1 year ago
At 4/1/2015 12:39:53 AM, MasturDbtor wrote:
At 3/30/2015 4:03:51 PM, UndeniableReality wrote:
At 3/30/2015 4:11:47 AM, MasturDbtor wrote:
Science used to think that in adulthood it was impossible for the brain to generate new cells.

And now we know that at the very least neurogenesis occurs in the hippocampus. We also know that it relates to our experiences. For instance London Taxi Drivers grew new neurons on the job.

It makes me wonder what evidence did they have before that they were going on to say positively that neurogenesis could not occur, as opposed to saying that it was inconclusive and that they did not know whether it could occur or not?

Anybody know this? I'm curious to know what mislead scientists on this.

You may also want to look up some of the work by Neil Burgess and Sue Becker who are current players on this topic. The Byrne Becker Burgess model might be fun to play with as well, if you're familiar with Matlab coding. I can send you a link to the code if you'd like.

I would. Thank you.

Sent in a PM.
MasturDbtor
Posts: 45
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4/3/2015 1:02:41 PM
Posted: 1 year ago
At 4/1/2015 9:52:52 AM, UndeniableReality wrote:
At 4/1/2015 12:39:53 AM, MasturDbtor wrote:
At 3/30/2015 4:03:51 PM, UndeniableReality wrote:
At 3/30/2015 4:11:47 AM, MasturDbtor wrote:
Science used to think that in adulthood it was impossible for the brain to generate new cells.

And now we know that at the very least neurogenesis occurs in the hippocampus. We also know that it relates to our experiences. For instance London Taxi Drivers grew new neurons on the job.

It makes me wonder what evidence did they have before that they were going on to say positively that neurogenesis could not occur, as opposed to saying that it was inconclusive and that they did not know whether it could occur or not?

Anybody know this? I'm curious to know what mislead scientists on this.

You may also want to look up some of the work by Neil Burgess and Sue Becker who are current players on this topic. The Byrne Becker Burgess model might be fun to play with as well, if you're familiar with Matlab coding. I can send you a link to the code if you'd like.

I would. Thank you.

Sent in a PM.

Didn't go through.