Posted on 12/10/2001 8:29:43 AM PST by RightWhale
No Evidence Of New Neurons In Adult Primate Neocortex
Neuroscientists have not found any evidence that adult primates are able to create new neurons in the most sophisticated part of the brain, the neocortex, according to the results of a study published in today's issue of the journal Science.
The results from scientists at Yale University and the University of Rochester run counter to a widely publicized report two years ago when other researchers reported the first discovery of neurogenesis -- formation of new neurons -- in the neocortex of adult monkeys.
The new findings, in a study funded by the National Institutes of Health, come from David Kornack, assistant professor of neurobiology and anatomy at the University of Rochester, and his former adviser, neuroscience pioneer Pasko Rakic of Yale.
"As a neuroscientist, oftentimes the first question I'm asked when I meet someone is, 'How can I get more brain cells?' I'm as interested in the question as everyone else," says Kornack. "It's now apparent that although some parts of the primate brain do acquire new neurons in adulthood, the neocortex is not among these regions."
For decades, scientists believed that adult humans and other primates such as monkeys are born pretty much with all the nerve cells, or neurons, in the brain that they'll ever have. However, in the last few years, several scientists equipped with new imaging techniques have reported growth of new neurons in adult primates including monkeys and humans in certain older parts of the brain, such as the hippocampus, which is key to memory, and the olfactory bulb, which is important for smell.
Two years ago, the idea took a giant step forward when researchers reported new neurons growing in the neocortex of adult monkeys. The neocortex -- the wrinkled outer layer of the brain -- is the most evolved part of the brain, controlling our most sophisticated behaviors such as language and planning.
The birth of new neurons in that part of the brain could have vast implications for human health and for understanding how the neocortex performs its sophisticated duties.
However, in the study published this week in Science, Rakic and Kornack used the most sophisticated cell analysis techniques available and found no new neurons in the neocortex of adult monkeys despite painstaking analysis of thousands of new cells in the neocortex.
The team used two separate molecular markers to key in on candidates for new neurons, then used laser-based confocal microscopy to look closely at every candidate. They found that oftentimes a cell seemed to carry both signals, flagging it as a newly created neuron, but that when the team looked closely, the "new neuron" turned out to be two separate cells, usually one "old" neuron and one newly created cell of a different type, such as a glial cell.
The pair did find new neurons in the hippocampus and the olfactory bulb. And they did find new cells of other types, such as glial cells, in the neocortex. But the pair, who comprised one of the first teams of scientists to discover that new neurons can be made in the hippocampus of adult primates, did not detect a single new neuron in the neocortex, an idea which caused much excitement among neuroscientists two years ago.
One upshot of the new findings, Kornack says, is that scientists should look to mechanisms besides neurogenesis to understand the workings of the neocortex, such as how we learn and store memories over a lifetime. The work could also affect the development of therapies that use adult stem cells to replace neurons lost to brain injury or neurodegenerative diseases such as Parkinson's or Alzheimer's.
"If we can find out what allows stem cells in those few restricted brain regions to continue producing neurons into adulthood, perhaps we can mimic that magic in other areas of the brain -- such as the neocortex -- that can suffer neuronal loss but don't normally make neurons," says Kornack, who left Yale to join the University of Rochester faculty last year. He is part of the University's Center for Aging and Developmental Biology. - By Tom Rickey
Could new groups be added --as in adding a new lobe or replacing a lobe in its entirety-- and would the new lobe communicate with the existing structure? Could I have a lobe added to replace my missing aesthetic lobe?
I suspect that many of the crucial functions of the brain are established during development. Replacements of whole areas of the brain might well survive but communicate very little with existing structures, resulting in a reduced "you". The stem cell panacea is based on the notion that new development takes place in a context which directs the new cells to their proper function.
Indeed they are. Some symptoms of schizophrenia might be due to cross-wiring in the lower brain, whether acute and temporary or slowly developing and permanent. Some people see colors as part of their aesthetic reaction to objects. Read that in an old Smithsonian.
As if the organ knows what to do with fresh stem cells. This is a mystery. If that is actually true, why wouldn't a general subcutaneous shot of stem cells go to every place in the body they are needed and regenerate all lost or impared functions?
This is sort of what happens. Bone marrow stem cells, for instance, are released into the blood stream during the normal course of cell replacement. Once in the blood stream, they migrate to areas that need new cells. When these stem cells are injected into another person's veins, they migrate, in the same fashion, to areas of deficit.
Who gives the orders and provides the directions?
Interesting. Explains why my mom has always had the same problem. So maybe there's hope yet for some kind of, you-know-what therapy to replenish the right proteins in the right places to maybe do that, um, thing I want done, um, repair, that's it. (God I hate that syndrome!)
If you're really curious, and have at least some mathematical background, read this book: "Sparse Distributed Memory" by Pentti Kanerva
It's brilliant. It lays out a novel method of storing and retrieving data, and then rigorously analyzes the properties that such a memory device would have.
Interestingly, the storage method described has properties that are strikingly similar to human memory. For example, it can retrieve data via "reminders" that are only partially similar to the stored information; it has no fixed capacity, but overloading it tends to cause similar stored items to "blend together", with older data fading faster than more recently stored data; storing the same or similar data repeatedly helps to ensure long-lasting "memories"; and no piece of data is stored at any particular location -- if you cut chunks out of it, some memories lose coherence more than others, but none simply vanish.
Furthermore, it can have the "tip of the tongue" problem you describe, wherein it "knows" that it knows something, but can't manage to retrieve it at the moment.
Finally, the actual method of storage is both incredibly simple, *and* very well suited for being implemented in a device that is "grown" instead of meticulously arrayed -- and the more elements the memory device has, the crisper the memories will be. You could make one by building millions of identical components, and letting each one randomly decide what memory location it wants to be (with no problems caused by any two deciding to be the same location, or by none deciding to be any particular location). So an undiffentiated mass of neurons would be suitable for memory storage of this type.
Finally, the last section of the book shows a schematic drawing of how neurons in the human cerebellum are connected, and the layout looks strikingly similar to how a device built to implement the author's design would be constructed. (The cerebellum is the seat of "muscle memory", i.e. physical coordinations learned over time by repeated practice.)
The same storage technique, slightly altered, is also suitable for the storage of time-based data, such as speech and songs, and the technique would make it easy to retrieve succeeding data given a short passage from the middle of a sequence (just as humans can mentally "play through" their memory of an old song after you play a few bars for them from any point -- the memory floods back after you've heard a piece of the song again.)
It's a fascinating book, and I think the author is really on to something.
Some further reading
Actually, the ape is smarter, though. He doesn't pretend to be presidential material! Is there anything more ignorant than self-delusion?
That is truly amazing. This "behavior" must be programmed in the DNA. It is mind-boggling to consider that each of the specialized stem cell types is a slightly different program and these differences are also somehow coded into the DNA. What is a head scratcher is how the symmetry is broken since all start from one and a division should produce identical copies. I presume the mechanism is a sort of beat the clock race. The first cell to achieve the new type inhibits the twin cell from also differentiating. In terms of organism development this race must be modified by position, otherwise our noses might end up next to our other cheeks. At least that is my guess.
Let me guess… LOL!!!
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