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Natures natural brain plasticity


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Old 26-04-2012, 11:15 PM   #1
John Nicholson
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Natures natural brain plasticity

Natures natural brain plasticity
Research Showing The Natural Changes Which Take Place When Areas Of The Brain Are Damaged

I have used this research to demonstrate how our complex brain manages to reorganise itself quite naturally when the brain is damaged before birth or after birth


Brain areas that serve specific functions for vision or hearing can take on a corresponding role for other senses in people who are blind or deaf.
By Cararl Sherherhermanan
Do the blind hear better, and the deaf see better, than those whose senses are intact? Some consider this widely held belief mere folklore, but recent research has verified the reality of cross-sensory enhancement, and offered insights into the neuroplasticity behind it.
There is ample evidence that the brain reorganizes in people who have sensory deficits. For example, the occipital cortex, which normally responds to visual stimuli, is activated by sound and touch in people who were blind from birth. Without this compensation, other senses suffer: in one famous case, reported in 2000, a blind woman lost the ability to read Braille after a stroke damaged her visual cortex. By temporarily disrupting occipital function with transcranial magnetic stimulation, researchers distorted tactile sensation in blind volunteers in a 1997 study.
New research has gone further, suggesting that precisely defined areas, or modules, that normally serve specific functions for vision or hearing can assume a corresponding role for other senses in the reorganized brain.
Researchers at Georgetown University tested the ability to localize and identify sounds and tactile sensations in people who had been blind from birth or infancy. Using functional MRI, they saw changes in brain activity in a part of the visual cortex, the middle occipital gyrus (MOG), that normally participates in locating objects of sight.
The MOG was more markedly activated, the researchers found, when the subjects tried to localize sound or touch. The stronger the activation, the better the subjects were at locating sounds.
“We showed that a specific region within the occipital cortex is involved preferentially in processing spatial information, regardless of modality,” says Josef Rauschecker, professor of physiology and biophysics at Georgetown University, and senior author of the paper, which appeared in the Oct. 7, 2010 issue of Neuron. The correlation between localization accuracy and activity in the MOG suggested that compensation through reorganization is “real, and not trivial,” he says. “Adding a chunk of occipital cortex to auditory processing ability is like having a computer with twice the capacity.”
A study reported in Nature Neuroscience a few days later makes an even stronger case for cross-modal plasticity of specialized brain areas. Researchers led by Steven Lomber of University of Western Ontario led congenitally deaf and normal cats through a series of visual tests. The deaf cats were superior in peripheral vision and movement detection. “This is similar to what has been found in deaf human subjects,” says Lomber.
Using cooling loops implanted in the cats’ brains, the researchers deactivated four areas of the auditory cortex in turn. When they chilled one area, the posterior auditory field, the deaf cats’ peripheral vision became no better than that of the hearing cats. Deactivating another area, the dorsal zone, left their peripheral vision superior but took away their edge in movement detection.
“When visual functions reorganize in deaf auditory cortex, they do so in a specific, not a random way,” says Lomber, noting that the PAF localizes sound in hearing animals, and the DZ is believed to have a role in detecting the movement of sound.
The “double dissociation” shown by the researchers—turning off area
When Senses Re-Align
Winter 2011
Image by permission of Current Biology, http://bit.ly/CurrentBiology
Areas activated by a sound localization task in congenitally blind (red) overlap with area activated by visual localization in sighted individuals (white).
(Continued on page 2)
Winter 2011/ 1
BrainWork / Summer 2009 / 2
A blunted function A but left function B intact, and vice versa—was an extremely convincing demonstration that “enhanced visual faculties are localized to well-defined auditory subcortices,” says Daphne Bavelier, director of the Brain and Vision Lab at University of Rochester, who was not involved with either new study.
“It’s nice to see research with different species, on different sensory modalities, reaching the same conclusion,” she says. Taken together, the Lomber and Rauschecker papers suggest “a principle for the functional organization of cross-modal plasticity that didn’t exist before.”
The Brain Remakes Itself
Plasticity comes naturally to “metamodal” parts of the brain, says Rauschecker. “As other neuroscientists have suggested, areas previously considered unisensory apparently have ‘hidden inputs’ from other senses: the visual cortex also receives auditory and tactile signals. Sometimes the input is inhibitory,” he said, noting that in his sighted control subjects, the occipital cortex area was deactivated by sound and touch. “In the blind, what may be happening is that the hidden inputs get stronger, and the balance shifts from visual to nonvisual.”
Time is a factor: Can the brains of those whose senses are impaired later in life compensate as well?
In an fMRI study published in Current Biology on Oct. 20, 2010, researchers led by Marina Bedny, a post-doctoral fellow at MIT, studied the middle temporal complex (MT/MST), a brain region that normally responds to visual motion. They found that the area was activated by moving sounds in congenitally blind adults, but not in sighted controls. Adults who had lost vision at age 9 or older reacted like controls: their brains lacked the reorganized circuitry of those born blind.
One person, who became blind between the ages of 2 and 3, similarly showed no more evidence of MT/MST activation by sound than those with normal sight. “These data are suggestive of an early sensitive period within the first couple of years of life in MT/MST development,” the authors wrote.
“If you’re young enough when you become blind, you can use the brain wiring that would have been used for sight to drive brain areas with a different input,” suggests Alvaro Pascual-Leone, director of the Center for Non-Invasive Brain Stimulation and professor of neurology at Harvard Medical School, who was senior author of the paper. “But if you lose sight later on, when you’ve already shaped connections on the basis of vision, the degree of reorganization may be limited by the scaffolding that’s already in place.“
There is probably no single, absolute “critical period,” he suggests; rather, plasticity is likely to depend on the faculty involved (such as motion detection), and the nature of early experience.
The researchers used fMRI to trace how the brain reconfigures itself. Their analysis of “functional connectivity”—a map of which brain areas were activated together—indicated that new links had been forged between the prefrontal cortex and MT/MST in those born blind.
“This interesting and somewhat unexpected finding suggests that connections are modified top-down—it’s not so much what comes into a given area from the eye or ear, as how the brain chooses to set itself up,” says Pascual-Leone. “We shouldn’t think of brain organization as a consequence of sensory input, but rather that the brain is a creative hypothesis-building machine that generates expectations, then confronts the world with them.”
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Old 26-04-2012, 11:23 PM   #2
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Sharpening Senses


Researchers hope to use what they learn about cross-modal plasticity to improve the lives of people with sensory deficits. One obvious possibility involves prosthetic devices: Goggles to translate visual images into sound patterns are already on the market, Rauschecker notes, and he is collaborating in research to make them more effective. Other inventors are exploring technologies to further enhance the capacity of remaining senses, such as GPS devices.
Knowing how brain connectivity shifts in people who are blind or deaf could help caregivers develop strategies of rehabilitation to “leverage other senses to substitute for lost faculties,” Pascual-Leone conjectures. Cognitive ‘priming’ exercises that modulate attention and employ guided imagery, for example, might enable reconfigured brain circuits to “extract even more information and benefit from cross-sensory input.”
Recovery of a lost sense, once an isolated occurrence, is becoming conceivable on a broad scale: as of March 2009, 188,000 people worldwide have received cochlear implants, according to the National Institute on Deafness and other Communication Disorders, and retinal implants are under development. Brain research may answer emerging questions about the ideal age for implants, and perhaps suggest strategies to help the formerly blind or deaf brain restructure itself a second time.
“Getting a good signal from an implant isn’t just a matter of opening a faucet,” says Bavelier. “We have to make sure the brain can use the information.”
“We need to know what the deaf brain is up to, before introducing a cochlear implant,” says Lomber. “Now that we see how it’s actually functioning differently, it may lead to the development of different implants, or different rehabilitation strategies for those who receive them.
Carl Sherman is a science writer
in New York City
Winter 2011
Image by permission of Current Biology, http://bit.ly/CurrentBiology
Functional magnetic brain imaging shows greater functional connectivity (red circles) between medial temporal (MT) cortex and prefrontal cortex in congenitally blind but not late-blind people vs. sighted people. The MT-visual cortex areas (blue circles) show reduced functional connectivity in both congenital and late-blind people.
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