Learning, adaptation can change brain connections, CMU researchers say
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Scientists used to think that the structure of the human brain didn't change much after infancy.
But in the past 20 years, there has been an explosion of studies showing just how adaptable and malleable the human brain is, and one of the most intriguing was published today by Carnegie Mellon University scientists.
Writing in the journal Neuron, brain researchers Marcel Just and Timothy Keller said that after just six months of intensive remedial reading instruction, children who had been poor readers were not only able to improve their skills, but grew new white-matter connections in their brains.
Even though the 35 third- and fifth-graders didn't achieve the same skill level as a group of 25 excellent readers, their white-matter connections in one particular pathway on the left side of their brains became just as strong as those in the top reading group. Meanwhile, 12 poor readers who attended regular classes showed no change in the connecting tissue.
White matter gets its name from the fatty myelin sheaths that encase the nerve fibers that connect one "thinking" area of the brain with another. It makes up half the brain's volume, and the Carnegie Mellon study is one of the few that has shown that the brain can actually change its connections through learning and adaptation.
There is a growing appreciation for how important these white-matter pathways are for helping the brain perform complex cognitive tasks.
The Just-Keller team had already shown in an earlier study that the white-matter tracts are disorganized in adults with autism. Now they have shown that the white matter in children with reading disabilities can be reorganized for the better.
To measure the changes, the scientists used a brain scanning technique called diffusion tensor imaging, which detects the changes in water flow along the white matter pathways.
Dr. Just said he was not particularly surprised that the children who got remedial training didn't end up as skilled as the best readers in their classes.
"It's kind of like taking people with a physical disability and giving them training but then saying they're still not as good as professional athletes," he said.
That is similar to another recent study at the University of Oxford in the United Kingdom that involved juggling.
In that project, researchers did brain imaging on 48 adults, and then asked half of them to practice juggling for 30 minutes a day for six weeks.
At the end of that study, the jugglers showed new white matter connections in a part of the brain involved in grasping and peripheral vision, said Heidi Johansen-Berg, as well as denser gray matter above those tracts.
But there was still a wide variety of skill levels among those who had the same white-matter growth, she said. Some were still doing basic three-ball juggling, while others were doing "five balls or reverse cascade juggling," she said.
Her group concluded that the white-matter improvements had more to do with how many hours people trained than how good they were.
There is no doubt, though, that people are able to improve the wiring in their brains with training, she said, and "studies like these highlight the importance of these communication networks in the brain."
While the reading improvement was modest in the local students, who came from all over Allegheny County, the benefits they got shouldn't be discounted, Dr. Just said.
"It means they can read newspapers and textbooks, which they once had difficulty with, and imagine the bootstrapping effect of that, so that maybe the reading process will become less effortful over time and everything will feed on itself."
It also cements the idea that learning can actually change the physical contours of the brain, he said.
"We all know that we learn things and we can do things we didn't used to be able to do. But it's one thing to know it, and another to say, here's how it happens. It really is something new to reveal part of the mechanism by which physical changes occur in the brain."
One finding that Dr. Just and Dr. Keller are still trying to unravel is the fact that the white-matter pathway that improved in the readers does not correspond to the gray matter areas that are known as the "reading circuit."
The front end of the pathway is in an area that helps decode words, but the back end is in a region that is part of the brain's "default network," which is active when people are daydreaming or not thinking about a particular task.
That led Dr. Keller to speculate that perhaps as the young readers got better, the white-matter signals dampened down distracting thoughts, so that they could devote more mental resources to reading.
It isn't just white-matter structures that can change in the brain.
Natasha Lepore, a brain researcher now at the University of Southern California, has shown that in people who became blind before the age of 5, the rear parts of their brains involved with vision have shrunk, as might be expected, but their frontal lobes have increased in size to compensate.
And an earlier study of London taxi drivers showed that a part of their brains' hippocampus, which is involved in memory, was much bigger than in other people after the drivers had gone through the city's rigorous training in learning the streets of the metropolis.
For those who improve their reading ability, it is possible the structural changes in their brains will have broader cognitive benefits, said Guinevere Eden, a Georgetown University researcher who is president of the International Dyslexia Association.
Dr. Eden, who praised the Carnegie Mellon study as an important advance in understanding how reading reshapes the brain, said a study done on Portuguese villagers has shown that children who were taught to read had noticeably different white-matter connections in their brains than siblings who were illiterate.
"We know that early on in life, there are a lot of changes in white-matter tracts in the developing brain. Now we have a study that shows that when you train kids in reading, you change their white matter to where it should be. And that helps show that anybody who has acquired literacy will manifest different brain anatomy and physiology than non-readers."
Dr. Just sees a broader lesson.
Studies like his show that "we're not at the mercy of our biology."
"I think that's a fruitful way to think about life and society in general -- I truly believe that some day, there's going to be a cabinet secretary of the brain."
First Published December 10, 2009 12:00 am