Neuroplasticity
1948637
225636970
2008-07-14T17:50:52Z
FrancineEisner
7445935
[[Image:Brain 2.jpg|right|thumb|300px|Neuroplasticity challenges the idea that brain functions are fixed in certain locations.]]
'''Neuroplasticity''' (variously referred to as '''''brain plasticity''','' '''cortical plasticity''' or '''cortical re-mapping''') refers to the changes that occur in the organization of the [[brain]] as a result of experience. A surprising consequence of neuroplasticity is that the brain activity associated with a given function can move to a different location as a result of both normal experience and recovery from brain injury.
The concept of neuroplasticity pushes the boundaries of the brain areas that are still re-wiring in response to changes in environment. Several decades ago, the consensus was that lower brain and neocortical areas were immutable after development, whereas areas related to memory formation, such as the [[hippocampus]] and [[dentate gyrus]], where new neurons continue to be produced into adulthood, were highly plastic.<ref>"Neurogenesis in adult primate neocortex: an evaluation of the evidence" Nature Reviews Neuroscience 3, 65-71 January 2002</ref> [[Hubel]] and [[Torsten_Wiesel|Wiesel]] had demonstrated that ocular dominance columns in the lowest neocortical visual area, V1, were largely immutable after the [[critical period]] in development.<ref>"The period of susceptibility to the physiological effects of unilateral eye closure in kittens"J Physiol Vol 206 1970, Issue 2 pp 419-436</ref> Critical periods also were studied with respect to language; the resulting data suggested that sensory pathways were fixed after the critical period. However, studies determined that environmental changes could alter behavior and cognition by modifying connections between existing neurons and via neurogenesis in the hippocampus and other parts of the brain, including the cerebellum<ref name=Ponti>Ponti et al. Genesis of Neuronal and Glial Progenitors in the Cerebellar Cortex of Peripuberal and Adult Rabbits. PLoS ONE, 2008; 3 (6): e2366 DOI: 10.1371/journal.pone.0002366</ref>.
Decades of research have now shown that substantial changes occur in the lowest neocortical processing areas, and that these changes can profoundly alter the pattern of neuronal activation in response to experience. According to the theory of neuroplasticity, thinking, learning, and acting actually change both the brain's physical structure, or [[anatomy]], and functional organization, or [[physiology]] from top to bottom. Neuroscientists are presently engaged in a reconciliation of critical period studies demonstrating the immutability of the brain after development with the new findings on neuroplasticity which reveal the mutability of both structural and functional aspects. A substantial paradigm shift is now under way: Canadian psychiatrist [[Norman Doidge]] has in fact stated that neuroplasticity is "one of the most extraordinary discoveries of the twentieth century."<ref name=Doidge>Doidge, Norman. ''The Brain that Changes Itself''. Viking, 2007, p. xv.</ref>
== Brain plasticity and cortical maps ==
Cortical organization, especially for the [[sensory system]]s, is often described in terms of [[cortical map|map]]s.<ref> CORTICAL PLASTICITY: From Synapses to Maps DV Buonomano, MM Merzenich - Annual Review of Neuroscience, 1998 </ref> For example, sensory information from the foot projects to one cortical site and the projections from the hand target in another site. As the result of this somatotopic organization of sensory inputs to the cortex, cortical representation of the body resembles a map (or [[homunculus]]).
In the late 1970s and early 1980s, several groups began exploring the impacts of removing portions of the [[sensation|sensory inputs]]. [[Michael Merzenich]] and [[Jon Kaas]] used the cortical map as their [[dependent variable]]. They found—and this has been since corroborated by a wide range of labs—that if the cortical map is deprived of its input it will become activated at a later time in response to other, usually adjacent inputs. At least in the somatic sensory system, in which this phenomenon has been most thoroughly investigated, JT Wall and J Xu have traced the mechanisms underlying this plasticity. Re-organization occurs at every level in the processing hierarchy to result in the map changes observed in the cerebral cortex.<ref>Wall JT, Xu J, Wang X.
"Human brain plasticity: an emerging view of the multiple substrates and mechanisms that cause cortical changes and related sensory dysfunctions after injuries of sensory inputs from the body." Brain Res Brain Res Rev. 2002 Sep;39(2-3):181-215. </ref> It is not cortically [[emergence|emergent]].
Merzenich and William Jenkins (1990) initiated studies relating [[sensory experience]], without pathological perturbation, to cortically observed plasticity in the [[primate]] [[somatosensory system]], with the finding that sensory sites activated in an attended [[operant behavior]] increase in their [[cortical representation]]. Shortly thereafter, Ford Ebner and colleagues (1994) made similar efforts in the [[rodent]] [[whisker]] barrel (also somatic sensory system). These two groups largely diverged over the years. The rodent whisker barrel efforts became a focus for Ebner, Matthew Diamond, Michael Armstrong-James, Robert Sachdev, Kevin Fox, and Dan Feldman, and great inroads were made in identifying the locus of change as being at cortical [[synapse]]s [[gene expression|expressing]] [[NMDA receptor]]s, and in implicating [[cholinergic]] inputs as necessary for normal expression. However, the rodent studies were poorly focused on the [[behavioral]] end, and Ron Frostig and Daniel Polley (1999, 2004) identified behavioral manipulations as causing a substantial impact on the cortical plasticity in that system.
[[Michael Merzenich|Merzenich]] and DT Blake (2002, 2005, 2006) went on to use [[cortical implant]]s to study the evolution of plasticity in both the [[somatosensory]] and [[auditory]] systems. Both systems show similar changes with respect to [[behavior]]. When a stimulus is cognitively associated with [[reinforcement]], its cortical representation is strengthened and enlarged. In some cases, cortical representations can increase two to three fold in 1-2 days at the time at which a new sensory motor behavior is first acquired, and changes are largely finished within at most a few weeks. Control studies show that these changes are not caused by sensory experience alone: they require learning about the sensory experience, and are strongest for the stimuli that are associated with reward, and occur with equal ease in operant and classical conditioning behaviors.
An interesting phenomenon involving cortical maps is the incidence of [[phantom limb]]s. This is most commonly described in people that have undergone [[amputation]]s in hands, arms, and legs, but it is not limited to extremities. The phantom limb feeling, which is thought{{Specify|date=August 2007}} to result from disorganization in the homunculus and the inability to receive input from the targeted area, may be [[annoying]] or [[pain]]ful. Incidentally, it is more common after unexpected losses than planned amputations. There is a high [[correlation]] with the extent of physical remapping and the extent of phantom pain. As it fades, it is a fascinating functional example of new neural connections in the human adult brain.
The concept of plasticity can be applied to molecular as well as to environmental events<ref>Georgetown University Medical Center (2008, July 12). Learning Suffers If Brain Transcript Isn't Transported Far Out To End Of Neurons. ScienceDaily. Retrieved July 13, 2008, from http://www.sciencedaily.com /releases/2008/07/080710120503.htm</ref><ref>Harvard University (2004, July 26). Scientists Pinpoint Molecules That Generate Synapses. ScienceDaily. Retrieved July 13, 2008, from http://www.sciencedaily.com /releases/2004/07/040726084801.htm</ref> The phenomenon itself is complex and can involve many levels of organization. To some extent the term itself has lost its explanatory value because almost any changes in brain activity can be attributed to some sort of "plasticity". For example, the term is used prevalently in studies of axon guidance during development, short-term visual adaptation to motion or contours, maturation of cortical maps, recovery after amputation or stroke, and changes that occur in normal learning in the adult.
Norman Doidge separates manifestations of neuroplasticity into adaptations that have positive or negative consequences. For example, if an organism can recover after a stroke to normal levels of performance, that adaptiveness could be considered an example of "positive plasticity". An excessive level of [[neuronal growth]] leading to [[spasticity]] or [[tonic paralysis]], or an excessive release of [[neurotransmitter]]s in response to injury which could kill nerve cells; this would have to be considered a "negative" plasticity. In addition, drug addiction and obsessive-compulsive disorder are deemed examples of "negative plasticity" by Dr. Doidge, as the synaptic rewiring resulting in these behaviors is also highly maladaptive<ref>Doidge, Norman. The Brain that Changes Itself. Viking, 2007</ref>.
==Treatment of brain damage==
Neuroplasticity is a fundamental issue that supports the scientific basis for treatment of [[acquired brain injury]] with goal-directed experiential therapeutic programs in the context of [[Rehabilitation (neuropsychology)|rehabilitation]] approaches to the functional consequences of the injury.
The adult brain is not "[[hard-wired]]" with fixed and immutable [[neuronal circuit]]s. There are many instances of cortical and subcortical rewiring of neuronal circuits in response to training as well as in response to injury. There is solid evidence that [[neurogenesis]], the formation of new nerve cells, occurs in the adult, mammalian brain--and such changes can persist well into old age.<ref>"Neurogenesis in adult primate neocortex: an evaluation of the evidence" Nature Reviews Neuroscience 3, 65-71 January 2002</ref> The evidence for neurogenesis is mainly restricted to the [[hippocampus]] and [[olfactory bulb]], but current research has revealed that other parts of the brain, including the cerebellum, may be involved as well<ref name=Ponti>Ponti et al. Genesis of Neuronal and Glial Progenitors in the Cerebellar Cortex of Peripuberal and Adult Rabbits. PLoS ONE, 2008; 3 (6): e2366 DOI: 10.1371/journal.pone.0002366</ref>. In the rest of the brain, neurons can die, but they cannot be created. However, there is now ample evidence for the active, experience-dependent re-organization of the synaptic networks of the brain involving multiple inter-related structures including the cerebral cortex. The specific details of how this process occurs at the molecular and ultrastructural levels are topics of active neuroscience research. The manner in which experience can influence the synaptic organization of the brain is also the basis for a number of theories of brain function including the general theory of mind and epistemology referred to as [[Neural Darwinism]] and developed by immunologist Nobel laureate [[Gerald Edelman]]. The concept of neuroplasticity is also central to theories of memory and learning that are associated with experience-driven alteration of synaptic structure and function in studies of [[classical conditioning]] in invertebrate animal models such as [[Aplysia]]. This latter program of neuroscience research has emanated from the ground-breaking work of another Nobel laureate, [[Eric Kandel]], and his colleagues at [[Columbia University College of Physicians and Surgeons]].
== Brain plasticity during operation of [[brain-machine interface]]s ==
[[Brain-machine interface]] (BMI) is a rapidly developing field of [[neuroscience]]. According to the results obtained by Mikhail Lebedev, [[Miguel Nicolelis]] and their colleagues {{ref_harvard|Lebedev|Lebedev ''et al.'' 2005|none}}, operation of BMIs results in incorporation of artificial actuators into brain representations. The scientists showed that modifications in neuronal representation of the monkey's hand and the actuator that was controlled by the monkey brain occurred in multiple cortical areas while the monkey operated a BMI. In these single day experiments, monkeys initially moved the actuator by pushing a joystick. After mapping out the motor neuron ensembles, control of the actuator was switched to the model of the ensembles so that the brain activity, and not the hand, directly controlled the actuator. The activity of individual neurons and neuronal populations became less representative of the animal's hand movements while representing the movements of the actuator. Presumably as a result of this adaptation, the animals could eventually stop moving their hands yet continue to operate the actuator. Thus, during BMI control, cortical ensembles plastically adapt, within tens of minutes, to represent behaviorally significant motor parameters, even if these are not associated with movements of the animal's own limb.
Active laboratory groups include those of [[John Donoghue (neuroscientist)|John Donoghue]] at Brown, [[Richard Andersen]] at Caltech, [[Krishna Shenoy]] at Stanford, [[Nicholas Hatsopoulos]] of University of Chicago, [[Andy Schwartz]] at [[University of Pittsburgh|Pitt]], [[Sandro Mussa-Ivaldi]] at Northwestern and [[Miguel Nicolelis]] at Duke. Donoghue and Nicolelis' groups have independently shown that animals can control external interfaces in tasks requiring feedback, with models based on activity of cortical neurons, and that animals can adaptively change their minds to make the models work better. Donoghue's group took the implants from Richard Normann's lab at Utah (the "Utah" array), and improved it by changing the insulation from polyimide to parylene-c, and commercialized it through the company [[Cyberkinetics]]. These efforts are the leading candidate for the first human trials on a broad scale for motor cortical implants to help quadriplegic or trapped patients communicate with the outside world.
== Thought and neuroplasticity==
The [[Dalai Lama]] invited [[Richard Davidson]], a Harvard-trained neuroscientist at the University of Wisconsin-Madison's W.M. Keck Laboratory for Functional Brain Imaging and Behavior to his home in [[Dharamsala]], India, in 1992 after learning about Davidson's innovative research into the neuroscience of emotions. ''Could the simple act of thinking change the brain?'' Most scientists believed this idea to be false, but they agreed to test the theory. One such experiment involved a group of eight [[Buddhism|Buddhist]] monk adepts and ten volunteers who had been trained in [[meditation]] for one week in Davidson's lab. All the people tested were told to meditate on compassion and love. Two of the controls, and all of the monks, experienced an increase in the number of [[gamma waves]] in their brain during meditation. As soon as they stopped meditating, the volunteers' gamma wave production returned to normal, while the monks, who had meditated on compassion for more than 10,000 hours in order to attain the rank of adept, did not experience a decrease to normal in the gamma wave production after they stopped meditating. The synchronized gamma wave area of the monks' brains during meditation on love and compassion was found to be larger than that corresponding activation of the volunteers' brains. Davidson's results were published in the Proceedings of the National Academy of Sciences in November, 2004 and TIME recognized Davidson as one of the ten most influential people in 2006 on the basis of his research.<ref>{{citation
| last1 = Lutz
| first1 = A.
| last2 = Greischar
| first2 = L. L.
| last3 = Rawlings
| first3 = N. B.
| last4 = Ricard
| first4 = M.
| last5 = Davidson
| first5 = R. J.
| date = 2004-11-16
| title = Long-term meditators self-induce high-amplitude gamma synchrony during mental practice
| journal = PNAS
| volume = 101
| number = 46
| pages = 16369-73
| url = http://www.pnas.org/cgi/content/full/101/46/16369
| accessdate = 2007-07-08}}</ref><ref>The Dalai Lama. [http://www.dalailama.com/news.112.htm “How Thinking Can Change the Brain"].</ref>
==See also==
* [[Eric Kandel]]
==Notes==
{{reflist}}
==Further reading==
*Donoghue JP, "Connecting cortex to machines: recent advances in brain interfaces." ''Nat Neurosci.'', 2002 Nov;5 Suppl:1085-8.
*Flor, H. (2002). "Phantom limb pain: Characteristics, causes, and treatments." ''Lancet Neurology'', 1: 182-189.
*Lebedev, M.A., Carmena, J.M., O’Doherty, J.E., Zacksenhouse, M., Henriquez, C.S., Principe, J.C., Nicolelis, M.A.L. (2005), [[Cortical ensemble]] adaptation to represent actuators controlled by a brain-machine interface. [http://www.jneurosci.org/cgi/content/full/25/19/4681 J. Neurosci. 25: 4681-4693]
*Ramachandran & Hirstein (1998). "The [[perception]] of phantom limbs", ''Brain'', 121: 1603-1630.
* [http://psyphz.psych.wisc.edu/web/News/Meditation_Alters_Brain_WSJ_11-04.htm Meditation Alters Brain Structure], from a [[University of Wisconsin-Madison]] website
* [http://www.nytimes.com/2007/05/29/health/29book.html The Brain: Malleable, Capable, Vulnerable], from a May 2007 article in ''[[The New York Times]]''
* [http://www.betterhumans.com/News/440/Default.aspx Monkeys Treat Robot Arm as Their Own] from betterhumans.com
* [http://www.medicinenet.com/script/main/art.asp?articlekey=47178 Monkey See, Robotics Do] from medicinenet.com
* Richard Davidson and Daniel Goleman Dialogue - Training the Brain: Cultivating Emotional Skills [http://www.morethansound.net/store/index.php?act=viewProd&productId=87]
==External links==
[http://iqtesttraining.com Implications of neuroplasticity to personal development -- '''Intelligence training''']
[http://www.sharpbrains.com/blog/2007/12/02/brain-fitness-program-and-neuroplasticity-pbs/ The PBS Program About Neuroplasticity -- '''Suggested Practices for Improving Brain Function''']
[http://www.sciencedaily.com/releases/2008/05/080512105712.htm Phantom Limb Pain and Neuroplasticity -- '''Additional Information''']
[http://www.sciencedaily.com/releases/2008/06/080604074911.htm '''Mammalian Neurogenesis in the Cerebellum''']
[http://www.sciencedaily.com/releases/2004/07/040726084801.htm Scientists Pinpoint Molecules That Generate Synapses in the Cerebellum -- '''Molecular Basis of Neuroplasticity''']
[http://www.eurekalert.org/pub_releases/2005-12/bu-wcc121405.php What Can Change in the Brain? Electrical Synapses, Research Shows -- '''Synaptogenesis and Brain Plasticity''']
[http://www.hhmi.org/news/svoboda20060622.html Long-Term Changes in Experience Cause Neurons to Sprout New Long-Lasting Connections -- '''Synaptogenesis Resulting from Novel Sensory Experience''']
[http://www.pbs.org/kcet/wiredscience/story/97-mixed_feelings.html Scientists Rewire the Brain through the Tongue --'''Neuroscientist Paul Bach y Rita''']
[http://www.eurekalert.org/pub_releases/2008-07/gumc-lll070308.php The importance of brain-derived neurotrophic factor (BDNF) in memory and learning; Synaptogenesis -- '''Molecular Basis of Neuroplasticity''']
[[Category:Neuroscience]]
[[Category:Neurology]]
[[Category:Neurophysiology]]
[[Category:Neurotrauma]]
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