The 100 billion neurons in your head have interconnected into a vastly complex network, and these connections can change and evolve as you "think" and "learn." Exactly how this network architecture is developed and even how individual connections are selected is not yet clear.

Image from PhysOrg.com

However, researchers from the Max Planck Institute for Neurobiology have experimentally verified that neurons have an even more efficient method for quickly selecting "good" connections from "maybe-not-so-good" connections, even before the critical synapse--the chemical controller that regulates communication between neurons--is fully developed.

The discovery shows that as an extension of a neuron (either a dendrite or axon) comes into contact with another neuron, a flood of calcium ions exchanges with the pair of cells and if certain threshholds are reached, then the growing connection will stick around long enough for a synapse to form; otherwise, it will retract and wiggle about growing into another direction.

The biological growth technique is observed to be quite efficient with "decision-making" for forming connections, in particular because synapse development can take much longer to complete. Even though the following article loosely suggests that this network connection technique "enables thinking," it's not necessarily the case that each time we have a "thought" that we are actually making a new, physical connection. Neural "learning" likely requires an evolution in the network structure, but our notion of "thinking" is likely related more to the patterns of electrical behavior in the existing network.

This work is also quite important for the future development of neurotechnological devices. For a pure neuron device to connect directly with a human brain, it will be required to have neurons living on the implanted device to grow extensions and interconnect directly with the subject brain... so, an understanding of how these connections develop and select one another will be absolutely vital for successful devices.

So, check out the following articles, and we'll be following the important developments.

This is an update to a previous Neuron News posting reviewing a new whole brain imaging technique--called Diffusion Spectrum Imaging--that tracks the flow of water molecules through axons to map neural interconnectivity. The research group has completed the imaging on a marmoset monkey, and the full three-dimensional animation of the result is now presented online.

The map was produced from a 24-hour scan of a dissected brain with a spatial resolution of 400 microns. View the animation and look closely at all of the intricate fiber pathways and interesting network patterns that are present. The level of complexity is not close to that of a human, but the system is certainly complex enough to begin the work on detailing the network to further understand brain function.

To be clear, each visualized pathway in the map does not represent a single axonal strand. However, it corresponds to hundreds of thousands of fibers that are all networked in approximately the same direction. So, this imaging technique does not resolve the network down to each individual connection, but an averaged view of large groups of connections.

The brain is a network. It is not just a lump of neurons. It's function and capabilities are entirely based on its structural characteristics as a network.

For neurotechnologies to be ultimately successful, a deep understanding of brain function will be required ... in other words, to connect into the brain we must understand the brain. And, this understanding requires a complete realization of the network structure that develops from a lump of neurons.

Recently published in PLoS Biology, is exciting research using a new method of brain imaging called diffusion imaging. This method uses magnetic resonance to monitor the movement of water molecules along the neuronal axons that are interconnected throughout the brain. This level of detail of a network map in a living brain has never been achieved before, and this initial work is just a first draft of low-resolution mapping.

Already in these low-res maps, intricate and even familiar structure is being discovered ... network structure that is also seen in other forms of complex networks, including the Internet. The main discovery is of a primary node that is super-connected to many other nodes located in the posterior medial and parietal cerebral cortex; i.e., the back of the head.

This is extremely critical work and very exciting. Remember, it's all about the network structure. This author is currently reviewing the published article, and will be updating Neuron News will an additional review soon.

Still, only in California.

Researchers from the Salk Institute for Biological Studies are bringing the control of brain cell development from in vitro to in vivo.

Stems cells -- in a petri dish -- are currently being routinely genetically converted into specific types of cells by introducing certain growth factors. Here, an injected retrovirus into the brain of a mouse to deliver a specific gene into adult stems is used to control stem cell development in vivo. It was previously shown that particular gene, called the Ascl1, converted neuronal stems cells into oligodendrocytes, the critical neuron network supportive cell that forms fatty insulation layers around axons to speed up the propagation of electrical signals.

The extremely exciting prospect of this discovery is the potential ability to increase the production of certain types of brain cells in patients where they are deficient. In particular, multiple sclerosis (more) is caused by the immune system killing off oligodendrocytes, so that neuron communication throughout the body is severely degraded. But, if replacement cells can be controlled, then the effects of the disease might be minimized.

"Adult Stem Cells Reprogrammed In Their Natural Environment" :: ScienceDaily :: July 1, 2008 :: [ READ ]

"Directed differentiation of hippocampal stem/progenitor cells in the adult brain" :: Nature Neuroscience :: Published online: 29 June 2008 [ READ ABSTRACT ]

Learn more about the researchers involved in the project:

• Fred H. Gage, Ph.D.,Laboratory for Genetics and the Vi and John Adler Chair for Research on Age-Related Neurodegenerative Diseases.
• Sebastian Jessberger, M.D., assistant professor at the Institute of Cell Biology at the Swiss Federal Institute of Technology in Zurich

Only in California. No, really.

With previous failures of converting embryonic stems cells only into supporting glial cells instead of general neurons, Stuart Lipton's research group at the Burnham Institute for Medical Research in La Jolla, CA recently discovered how to convert mice stem cells into neurons. These cells were then transplanted into a mouse brain and they successfully connected and functioned within the existing neuron network.

The work is funded from a four-year, $75 million grant (pdf) from the California Institute for Regenerative Medicine.

Understanding how stems cells transform into any of the hundreds of types of cells in the human body is still a challenge, but Lipton's team is focusing on the protein MEFC2 and how it links to the genes in the stem cell to tell it to turn into a neuron.

Although we're still far far away from doing clinical trials to throw these neurons into human brains and "see what happens", this research is critical just for further fundamental understanding of neuron cell development, growth, and function. How neurons grow and, in particular, how they interconnect with one another is a major factor in the overall resulting function of the brain. So, watching how a neuron is "born" (and understanding it so well that we can guide the process) and then interconnect will provide more insight into the function of a larger neuron network.

The research is published in The Journal of Neuroscience June 25, 2008 Issue [Read the abstract]

"Repairing damage to brain may be nearer" :: SignOnSanDiego.com :: June 25, 2008 :: [ READ ]

"Scientists repair brain using GM embryo cells" :: Telegraph.uk.co :: June 24, 2008 :: [ READ ]

Sophisticated brain imaging has never been able to directly image the activity of neurons (namely, fMRI and PET scans). Instead, the realization that active neurons caused increased blood flow to occur in the vicinity allowed researchers to develop the techniques that could more easily monitor the flow activity. As blood flow increased in a region of the brain, then the neurons in the area must also be screaming with increased activity.

But, neurons do not have a direct connection to blood vessels and blood flow in the brain.

The correlation between active neurons and the resulting blood flow changes has just now been directly realized by a team at MIT who used two-photon excitation microscopy developed by the lab of Watt Webb at Cornell University. They found that another very common cell that composes about 1/2 of all brain cells, called an astrocyte which directly affects blood flow and is electrically quite unlike the neuron, instead reacts to non-electrical stimuli from surrounding cells.

This is a rather significant discovery and further research will lead to a deeper understanding of how our complex neural networks function and how they stay alive in our heads.

.....

MIT unlocks mystery behind brain imaging :: PhysOrg.com June 19, 2008
[ read article ]

"Tuned Responses of Astrocytes and Their Influence on Hemodynamic Signals in the Visual Cortex"
James Schummers, Hongbo Yu, and Mriganka Sur
Science 20 June 2008: 1638-1643.
[ read abstract ]

Movies of visually evoked responses of neurons and astrocytes [ view ]

About Mriganka Sur at MIT

Picower Institute for Learning and Memory at Massachusetts Institute of Technology
[ visit ]

Of course, mounting a video camera into your skull isn't a pleasant idea. So, there are techniques that allow brain cells, called neurons, to be grown in other environments like glass dishes or silicon wafers. Coaxing the cells to actually survive in this foreign way is something of a black art, but when done successfully scientists have a great way to directly watch neurons do their thing.

An astounding recent advancement in imaging technology has pushed these movie makers to the next level with incredibly high effective frame rates. Just like a strobe light at a party make the dance floor look like a slow flashing of images before your hazy eyes, advanced, high-speed lasers can be pulsed very quickly to illuminate a field of view.

Jeff Lichtman, at the Washington University School of Medicine in St. Louis, MO, has taken advantage of this new technology to watch neuron development with such a high resolution. Scientists in other fields, such as chemistry, biology, and physics are also exploring important applications.

Read more about this exciting technology...

[ Read the article from Small Times ]

But how are these branches formed in the first place? How do the axons and dendrites know where to go so that the "correct" function results? This is an enormous question and many researches are experimenting with how neuron networks actually develop (this will later be highlighted in our upcoming academic research topical category).

Understanding this developmental process is critical to fabricating functioning neuron devices in silicon. If the neurons are to grow and live happily on a computer chip, then the environment on that chip must be just right for the finicky brain cell.

Also, if the route to fabricating the device is to have baby neurons grow their branching networks on their own (which is a typical method used by researchers), and if we want the device to result in a specific function, then it might be very important to know how to guide the growing branches to the appropriate neighboring neuron (although this will be an important point of debate).

John Thomas, a professor at the Salk Institute, has recently reported on an important discovery on a certain protein interaction occurring in the neuron's environment that signals to a growing branch to "go the other way!" Read more about this work, and consider how it could be a vital bit of biology that will aid in controlling how neurons may develop and live in a silicon world.

[ Read the article from ScienceDaily News ]

Don't loose your nerves. You might not get them back.

It's an well know "fact" that once a brain cell dies, it won't grow back. Scientists are continuing to discover that this is not always the case, as has been previously discussed here in Neuron News. More developments from a United States government lab is continuing to show that damaged nerve cells might be coaxed into rejuvenation.

Surya Mallapragada, an Ames Laboratory associate in Materials Chemistry, has developed micro channels in degradable polymers that can guide growing axons to fill in gaps of important nervous system wiring caused by some sort of damage.

There has been some success with nerves in rats, but they are still learning about how this approach will work in the central nervous system comprised of the brain, spinal cord and optic nerve.

[ Read the article from the Ames Laboratory ]

This is at least what scientists at the University Of South Florida Health Sciences Center are anticipating. Instead of plugging in a device that relies on silicon chip-interfaced brain cells to replace damaged nervous communication links, Prof. Samuel Saporta and his group directly transplant neurons grown from a special type of cancer cell. These neurons connect up with the existing network on their own without any outside control.

This is a very critical concept that we must understand in more detail, not only for the above application, but also for making neuron devices. If we want to be able to control the activity of an implanted device, we must be able to design the neurons in such a way that they will properly communicate with the recipient's existing neural network.

Neuron are capable of connecting up to other neurons in functional ways on their own, which an example of "self-organization" (to throw in a buzz-word). Before neurotechnologies will every be widely useful, we must understand the self-organizational properties of neurons--as has been indirectly witnessed by Saporta's team--in order to guide the proper development of neural prosthetic devices.

Once again, scientists are discovering new reasons why the adage that your brain cells never grow back is not entirely correct. The article below describes the recent results from Dr. Marc Tessier-Lavigne of Howard Hughes Medical Institute at Stanford University where his group fed a special molecule to a neuron and then cut it (in a rat, of course). The neuron's structures grew back after the injury giving some clues as to how we might be able to build on this technique to help humans repair a damaged nervous system.

In order for implanted neuron devices to successfully be used as a corrective tool for neurological disorders, it is critical that we have an understanding of exactly how the electrical activity between neurons corresponds to actual physical movement of the body.

A Princeton University team recently took electrical measurements in a monkey's brain suggesting that groups of neurons in the motor cortex (generally near the surface of the top of your brain) controlled complicated physical postures. This is in significant contrast to the prevailing view that these motor neurons only control specific muscles.

This is an interesting new look at brain function because it suggests that small clumps of interconnected neurons can direct much higher-level body function. This might make the barriers to better understanding the brain even higher, since we won't be able to attribute a single neuron or neuron group directly to a specific part of our body.

So, instead of thinking "this specific neuron that excites a muscle has to talk to this other neuron to excite another muscle, which then has to talk to this other neuron" in order to coordinate the lifting of a finger, we must think more in terms of networks of neurons collectively directing complicated behaviors. It really will become messy if we find different networked groups of neurons controlling the same set of muscles, but resulting in different physical behaviors.

Your mother always told you that you if you loose your brain cells to too much booze, then they won't ever grow back.

Contrary to this popular belief, scientists have found that baby neurons in rat brains can develop and form new, functional connections within established neuron networks. To see this "neurogensis" in action, a stain was introduced into the brain that would only make dividing cells glow. Younger neurons undergoing cell division appeared a distinctive fluorescent color, while the older, non-dividing neurons remained in the dark.

Of course, it is still an assumption that this phenomena occurs in humans as well. However, it is anticipated that by gaining an understanding of how neurogenesis works, scientists can develop therapeutic methods to help reverse degenerative conditions like Alzheimer's disease.

Your brain is absolutely remarkable. Because of the unique and complex method in which neurons organize themselves to keep your body alive and allow it to interact with the environment, a young girl in Holland with only 50% of her brain can now speak two languages.