BrainMeta'   Connectomics'  

Welcome Guest ( Log In | Register )

 
Reply to this topicStart new topic
> Can the brain actually rewire itself?...
dutch84
post Aug 17, 2006, 10:47 PM
Post #1


Aspiring
**

Group: Basic Member
Posts: 95
Joined: Apr 17, 2006
Member No.: 5115



...or does it just substitute lost function by utilizing areas that were previously not in use?

I personally think it is the latter.
User is offlineProfile CardPM
Go to the top of the page
+Quote Post
rhymer
post Aug 18, 2006, 11:23 AM
Post #2


Supreme God
*******

Group: Global Mod
Posts: 2093
Joined: Feb 27, 2003
Member No.: 385



Some research info here !

http://www.livescience.com/othernews/05122...ron_growth.html
User is offlineProfile CardPM
Go to the top of the page
+Quote Post
Paul King
post Oct 25, 2006, 12:27 AM
Post #3


Newbie
*

Group: Basic Member
Posts: 49
Joined: Aug 14, 2005
From: San Francisco, CA
Member No.: 4500



There is ongoing rewiring in the adult brain.

What is less common is the birth of new neurons. However there are some places in the brain where this happens as well.

The brain rewires itself through a decentralized process in which the neuronal connecting fibers (axons and dentrites) sprout new branches and grow outward in some direction. These new branches may disappear days or weeks after first appearing, or they may persist, become longer, and sprout new branches themselves.

It is believed that this process happens as a side-effect of the activity of the neuron and the other neurons that it is near. The idea is that memories are stored initially though changes in the strenghts of synapses. However over a long period of time, memories can eventually emerge as changes in the actual wiring structure of the brain. This is called structural plasticity (as opposed to synaptic plasticity).

While structural plasticity has been seen in action (and photographed with microscopic movies), not much is known about when and why it happens, and what its relationship is to other activies of the brain, or to the information stored in the neural networks.
User is offlineProfile CardPM
Go to the top of the page
+Quote Post
dentroid
post Nov 06, 2007, 11:48 AM
Post #4


Newbie
*

Group: Basic Member
Posts: 6
Joined: Nov 06, 2007
Member No.: 14175



Seems like nobody understand where memory is stored. There is two teories about rewireing and synapses strenght or one teory with those two components? That's to me strange does neuron changing streng of synapses of all synapses of his axon at same time or only some of this synapses change connection/conductivity strenghts?
User is offlineProfile CardPM
Go to the top of the page
+Quote Post
forgottenpresence
post Nov 07, 2007, 10:56 AM
Post #5


Overlord
****

Group: Basic Member
Posts: 289
Joined: Aug 20, 2007
Member No.: 12281



QUOTE(dutch84 @ Aug 17, 2006, 10:47 PM) *

...or does it just substitute lost function by utilizing areas that were previously not in use?

I personally think it is the latter.


Can the nervous system become aware of itself?
User is offlineProfile CardPM
Go to the top of the page
+Quote Post
Trip like I do
post Nov 07, 2007, 05:25 PM
Post #6


Supreme God
*******

Group: Basic Member
Posts: 5156
Joined: Aug 11, 2004
From: Earth^2
Member No.: 3202



Can the brain rewire itself of its own accord or does it require external factors to influence this rewiring?
User is offlineProfile CardPM
Go to the top of the page
+Quote Post
opfor101
post Nov 07, 2007, 05:59 PM
Post #7


Aspiring
**

Group: Basic Member
Posts: 65
Joined: Oct 27, 2007
Member No.: 13879



QUOTE(Trip like I do @ Nov 07, 2007, 08:25 PM) *

Can the brain rewire itself of its own accord or does it require external factors to influence this rewiring?


it really depends, external factors usually are needed.

complete rewiring of the brain is seen for example this guy
was hit on the left side of his head by a baseball at the age of 9 or 11
cant remember which

but ever since that day he was able to memorize weather, temperature of everyday since that day
and if you call out a random day which he experience he can call it instantaneously

rewiring is possible, but external factors usually are required.
User is offlineProfile CardPM
Go to the top of the page
+Quote Post
dutch84
post Dec 22, 2007, 12:19 PM
Post #8


Aspiring
**

Group: Basic Member
Posts: 95
Joined: Apr 17, 2006
Member No.: 5115



I sort of found my answer:

Learning and Memory: Rewiring the Brain

The mammalian brain appears most adaptive during the early postnatal period, and continues to adapt and learn from new experiences throughout its adult life. During the 1960s and 1970s a series of studies offered impressive evidence that rats grew thicker brains and new synapses when they were placed in complex and challenging environments. These findings were consistent with the then-popular belief that learning and memory in mature mammals (as opposed to the brain development of immature animals) were additive processes involving the formation of new synaptic connections or the strengthening of already existing ones. The influential Canadian psychologist Donald Hebb assumed that "the changed facilitation that constitutes learning" was the result of "the growth of synaptic knobs."[24] Similarly, Sir John C. Eccles, who shared a Nobel prize in 1963 for his research on the transmission of nerve impulses, believed that memory and learning involved "the growth . . . of bigger and better synapses."[25]

However, it was also suggested that more than just adding synapses was involved in learning. One of the first to propose that subtractive brain changes could be involved in adult learning and memory was J. Z. Young, who in 1964 posited that such learning could be the result of the elimination of neuronal connections.[26]Several years later J. S. Albus hypothesized that "pattern storage must be accomplished principally by weakening synaptic weights rather than by strengthening them,"[27] and Richard Dawkins speculated that the selective death of neurons could underlie the storage of memories.[28]

But how could a subtractive process of neuron elimination be involved in learning and memory? It is particularly difficult to understand how the learning of a new skill, such as riding a bicycle or speaking a foreign language, or acquisition of new memories, such as learning the words to a poem or song, could be made possible by loss of synapses. We saw in the development and maturation of the brain that synaptic connections that are rarely used are weakened or eliminated, whereas those in active neural pathways are retained and perhaps strengthened. This subtractive process makes sense when dealing with an overwired, immature brain that may have close to twice as many synapses as it will have as an adult. But how can it work for a mature adult brain that has already been substantially whittled down by synaptic pruning?

To illustrate this problem, imagine an adult Spaniard learning English. To do this, the Spaniard will have to learn to hear and produce certain sound distinctions that are not used in Spanish, such as the contrasts involved in ship versus sheep, sue versus zoo, and watch versus wash. The research of Werker and Tees would lead us to predict that the Spaniard would not initially be able to make these distinctions since they are not made in the language he has heard and spoken all his life. The synaptic connections necessary for making these discriminations were present when he was born, but we would expect them to have been promptly pruned away since they were not used in the language of his environment. It is therefore not clear how any further pruning of synapses would permit him to learn this aspect of the English language.

Instead, it seems more likely that a process involving the addition of new synapses, or at least reorganizing current ones, would be necessary for this learning to take place. But then we run into the equally thorny problem of understanding how the brain could ever know which new synapses to add or modify! Surely, some combination of synaptic changes should allow the Spaniard to learn English, since many adults learn English and other languages, and such learning must be the result of changes in the synaptic connections of the brain. But just which new combination of synapses will do the trick? At the very least it would appear that the brain would somehow have to try out a number of new combinations and select the best ones. But to select the best ones, a source of variation is necessary, perhaps not unlike the initial variation of synaptic connections present in the immature, overconnected brain.

A possible solution to this riddle was offered by French neurobiologist Jean-Pierre Changeux in 1983. In his book L'Homme Neuronal (published in English in 1985 as Neuronal Man), Changeux proposed a "Darwinism of the synapses"[29] to account for the development of the brain and the learning it undergoes within its cultural environment.

According to this scheme, culture makes its impression progressively. The 10,000 or so synapses per cortical neuron are not established immediately. On the contrary, they proliferate in successive waves from birth to puberty in man. With each wave, there is transient redundancy and selective stabilization. This causes a series of critical periods when activity exercises its regulatory effect.[30]

In effect, he was suggesting that all adaptive brain changes, or at least those occurring between birth and puberty in humans, involve the elimination of preexisting synapses, but that these preexisting synapses were not necessarily all present at the same time. From birth to puberty, Changeux hypothesized that waves of synaptic growth would occur, with subsequent experience serving to retain the useful ones and eliminate the useless and redundant ones. These waves of synaptic overproduction would provide the source of variation on which synaptic selection could operate. Such learning resulted in an absolute increase in synaptic growth and numbers over time. This growth was not constant, but was rather envisioned as analogous to repeatedly taking two steps forward--randomly adding new synapses--followed by one step backward--eliminating the useless ones just added.

Changeux provided no hard evidence for his hypothesis that synaptic variation in the form of overproduction would precede the elimination of synapses as part of the brain's restructuring to permit the learning of new skills and acquisition of new knowledge. But such evidence was found a few years after the publication of his book. William Greenough and his associates, whose work on the maturational development of the rat's brain was noted earlier, also conducted research on changes in the brain induced by placing adult rats in special, enriched environments. In one study this resulted in a 20% increase (roughly 2000) in the number of synapses per neuron in the upper layers of the visual cortex.[31] Later research showed that such dramatic increases in synapses were not restricted to the rat's visual cortex.[32]

These and other similar findings led Greenough's group to propose that the waves of synapse proliferation first described by Changeux could be elicited by the complex demands placed on the adult brain in a new, challenging environment. These researchers referred to this process as "experience-dependent" development since it depends on the environment triggering the formation of new synaptic growth on which the selective process can act.[33]

Greenough's conception of how the adult brain is able to learn new skills and form new memories offers an appealing solution to the problem concerning the additive and subtractive processes underlying the adult's brain adaptation to new environments. According to this theory, experience-dependent learning combines both additive and subtractive processes. The additive component involves the blooming of new synapses in response to the animal's attempt to control aspects of a new, complex environment. Although the brain does appear to know what part of itself has to be involved in this new synapse-construction project, it need not (indeed, could not) know which particular connections to make. By forming a large variety and number of new connections, the brain can select the combinations that work best, in the same way that the immature, developing brain retains useful connections from its initial oversupply of synapses. The long-term result is an overall addition to the number of synapses. But the actual selection process that fine-tunes the connections is a subtractive one in which the useful connections are selectively retained and less useful ones eliminated. Although clear evidence exists for synaptic increase in learning, as I write this we still have no such evidence in mature learning for an overproduction of synapses that are then pruned away. However, recent research has found evidence for an overproduction of dendrites in mature rats during readaptation of the brain after brain injury, which at least suggests that synaptic overproduction may be involved as well.[34] These findings fit very nicely with the subtractive synapse findings on brain maturation and provide a solution to the mystery of how the brain could know exactly which new synaptic connections to establish to enable it to acquire new knowledge, skills, and memories.

Although only a relatively small number of neuroscientists have opted for a selectionist approach to their research and theorizing, Changeux and Greenough and their associates are not the only ones whose research suggests that the adult brain develops and learns through a process of cumulative neural variation and selection. This theory has now been embraced and given additional support by several other leading neuroscientists. William Calvin refers to the brain as a "Darwin machine" that follows the plan "make lots of random variants by brute bashing about, then select the good ones."[35] Gerald Edelman, who shared a Nobel prize in 1972 for his research on the chemical structure of antibodies in the immune system, has contributed a remarkable outpouring of books describing aspects of his "neuronal group selection theory" of brain development and learning through a selectionist process he refers to as "neural Darwinism."[36]And noted psychologist and neuroscientist Michael Gazzaniga, best known for his ground-breaking research on humans with split brains, recently embraced a selectionist account of brain functioning and development.[37]

Current research is under way to determine whether unambiguous physical evidence can be found for the overproduction and elimination of newly formed synapses in the adult brain in response to environmental changes. Such a finding would place the brain alongside the immune system as another striking example of how cumulative variation and selection processes during the lifetime of an organism make it possible to adapt to complex, changing environments.

We have now seen that understanding both the adapted and adaptive complexity of the human brain involves finding answers to three questions: how did the brain originate as a biological organ?; how does it develop from a fertilized egg into a mature brain?; and how is it able when mature to rewire itself to learn from and adapt to changes in its environment?

Much more work must be done before we have detailed answers to these questions. But substantial progress has already been made as we move midway into the "decade of the brain." To a large extent this progress has consisted of rejecting providential and instructionist explanations for these puzzles of fit, and finding considerable evidence and reason in favor of selectionist explanations. The powerful process of cumulative blind variation and selection working over millions of years is not only the only reasonable theory for the biological evolution of the brain, but we find that it has surfaced again in a different but still recognizable form as an explanation for the brain's embryonic growth and continued development during its relatively brief lifetime.

It is here, as Changeux remarked, that "the Darwinism of synapses replaces the Darwinism of genes."[38] To close the circle, it should be noted that a striking consequence of the joint effects of among-organism genetic and within-organism synaptic selection is the brain's understanding both itself and the process of selection that is responsible for its extraordinary abilities.
User is offlineProfile CardPM
Go to the top of the page
+Quote Post
Yocttar
post Nov 19, 2008, 08:15 PM
Post #9


Newbie
*

Group: Basic Member
Posts: 30
Joined: Nov 06, 2008
Member No.: 31717



TY dutch84, very informative.
User is offlineProfile CardPM
Go to the top of the page
+Quote Post
Chronman
post Dec 18, 2008, 08:30 PM
Post #10


Newbie
*

Group: Basic Member
Posts: 2
Joined: Dec 18, 2008
Member No.: 31805



It can rewire itself, but thats a bit vague...

It can also "fill in the blanks", quite effectively.
User is offlineProfile CardPM
Go to the top of the page
+Quote Post

Reply to this topicStart new topic
1 User(s) are reading this topic (1 Guests and 0 Anonymous Users)
0 Members:

 



Lo-Fi Version Time is now: 19th November 2017 - 08:10 PM


Home     |     About     |    Research     |    Forum     |    Feedback  


Copyright BrainMeta. All rights reserved.
Terms of Use  |  Last Modified Tue Jan 17 2006 12:39 am

Consciousness Expansion · Brain Mapping · Neural Circuits · Connectomics  ·  Neuroscience Forum  ·  Brain Maps Blog
 · Connectomics · Connectomics  ·  shawn mikula  ·  shawn mikula  ·  articles