Thursday, March 10, 2011
Repurposed Sight Centers in the Brain
My sweet Ashley can use inappropriate language quite well. She signs it instead of speaking it, but I learned a long time ago, that not only was she making the signs correctly, she was using them in the correct context.
I've never really known where she learned those inappropriate signs. Most of them were ones I had never seen or used. Keep in mind that she is deafblind. More than likely she wasn't seeing the signs too clearly, even from her peers. But somehow she has learned them, and uses them well.
I may now have a few more clues into the functioning of her brain that helped her learn the signs and learn to use them appropriately. Checkout this post from a blog titled, "Wired Science". This is fascinating - well, at least to me!
In the brains of people blind from birth, structures used in sight are still put to work — but for a very different purpose. Rather than processing visual information, they appear to handle language.
Linguistic processing is a task utterly unrelated to sight, yet the visual cortex performs it well.
“It suggests a kind of plasticity that’s even broader than the kinds observed before,” said Marina Bedny, a cognitive neuroscientist at the Massachusetts Institute of Technology. “It’s a really drastic change. It suggests there isn’t a predetermined function an area can serve. It can take a wide range of possible functions.”
In a study published Tuesday in the Proceedings of the National Academy of Sciences, Bedny’s team monitored the brain activity of five congenitally blind individuals engaged in language-intensive tasks.
Immense neurological plasticity was suggested by research conducted in the late 1990s on “rewired” ferrets — after their optical nerves were severed and rerouted into their auditory cortices, they could still see — but such studies, already ethically troubling in animals, would be unconscionable in humans.
Instead, researchers have used brain imaging to study plasticity resulting from natural sensory deprivation in people. They’ve found that the visual cortices of blind people become active as they read Braille. It wasn’t clear, however, whether this was a function of Braille’s spatial demands, which overlap with the spatial aspects of sight, or a radical repurposing of supposedly specialized areas.
In Bedny’s study, the brains of blind people were analyzed as they listened to complete sentences — a relatively high-level comprehension task. Then they were given lesser linguistic challenges, from listening to lists of unrelated words to hearing sentences played backwards, or trying to comprehend grammatically structured speech containing nonsense words.
The results were twofold. Blind people’s visual cortices clearly responded to language, not to space. Moreover, they were most active in response to high-level language demands, just as the brain’s “traditional” language centers are.
Implications of the findings are many. Some neuroscientists have proposed that human brains are hard-wired for language, with specific regions evolved for the task. While our brains are obviously well-suited for language, its performance by visual centers suggests that more than hard-wiring is at work.
“Language is a property that emerges out of the system, rather than a magic-bullet solution from one brain area,” said Bedny.
Indeed, the brains of congenitally blind people may even hint at the human brain’s early state, with “visual” centers open for processing different types of information, and only later becoming involved in vision.
Bodny is now using behavioral tests to investigate in greater detail how blind people process language. “We really want to know what sort of things are blind people better at,” she said. “Parsing complicated sentences, with different grammatical structure? Might they be better at resolving ambiguities? If they’re listening to several things at a time, can they parse two speech streams rather than one? We don’t know the answer to those questions yet.”